Conceptual Class Notes Semester 2

bankercordMechanics

Oct 27, 2013 (3 years and 9 months ago)

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1































2




Energy


Work, Power, and Energy


Activity: Burning Calories Walking


Activity: Horsepower






Forms of Energy






Conservation of Energy






Lab: Conservation of Energy






Machines







Efficiency


Circular Motion


Rotation and Revolution


Centripetal Force






Temperature, Heat, and Expansion






Temperatu
re






Heat






Specific Heat






The High Specific Heat of Water






Thermal Expansion




Heat Transfer






Conduction, Convection, and Radiation






Radiation and Newton’s Law of Cooling






Activity:
Coffee Lab


3


Thermodynamics






First Law of Thermodynamics






Second Law of Thermodynamics






Carnot Heat
Engines














Vibrations and Waves






Wave Description






Interference






Standing Waves






Doppler Effect and Shock waves






Sound






Properties of Sound






Loudness






Making Sound Louder






Lab: Calculating the Speed of
Sound






Sound Interference


Light


Properties of Light


Transparent and Opaque Materials


Polarization




4


Reflection and Refraction






Reflection






Refraction






Dispersion of Light and Rainbows






Total Internal Reflection


Color

How we
see color






Light Addition






Light Subtraction






Color Wheel






Lenses


Concave and Convex Lenses


Ray Diagrams


Properties of Lens Images


Activity:
Calculating Focal Lengths








Semester Review





5






Chapter
9

Highlights:





Work,
Power, and Energy

Forms of Energy

Conservation of Energy

Machines





Efficiency





Key Terms










Energy

Work

Power

Work
-
Energy Theorem

Heat

Potential Energy

Kinetic Energy

Law of Conservation of Energy

Potential Energy

Work
-
Energy Theorem

Fulcrum

Mechanical Advantage

Lever

Pulley

Inclined Plane

Efficiency


6

What is energy?

Energy is the ability to do work

What does it involve?

Mass, motion
and/
or position

Does this
shotput have energy when it is on the floor?

No, it will not do anything.

What happens when the shotput is lifted above the floor?

It has energy do to it having the ability to do work on other things.

What happens when the shotput is kicked?

It has energy
to do work too.

How do we know that each of the two previous situations, the shotput had
energy? Explain

It will cause damage. It will create a force acting on other objects when it
collides.

Energy



(units =
Joules
)
-

the ability to do work.



Work



(units =

Joules
)
-

the force applied parallel through a distance that
changes the energy state of an object.

W = F d

Where did the energy to do the work come from?

The work done by the
person lifting the object


the work came from the
chemical energy of the food that was eaten.

Do activity: Burning Calories while walking


7



How far do you need to walk in order to burn off the calories in one snack
size candy bar?

Calories in one candy bar = _____________ Cal. = ____________ J


Weight of student = ____________ lbs. = ___________ N




the

center of gravity of the student is raised and lowered with each
step.

One step changes the persons center of gravity = __________ cm

Therefore the total change in distance is (x 2) = __________ cm

Calculate the work performed by the student to do one ste
p:




Calculate the number of steps to burn off the equivalent amount of Joules in
one candy bar:





Calculate the distance traveled to burn off the candy bar:

The distance of one step = ___________ m





Apply the efficiency of a person to get the actual

distance needed to burn
off the Calories, use 15%.





8

What is the difference between these two situations?

Weight

lifted to
desk by a student:

Weight

lifted to desk by teacher:

Student lifted it faster


in less time.

Do they both involve the same amount of work?

Yes, same distance and same weight.

Power



(units =
Watts
)
-

the rate of work done per unit time, the change in
energy per unit time.

P =
W/t

=
F d /t = F v

American units =
horsepower



SI units =
watts

Why aren’t light bulbs measured in hp?

Too large of units, hp is related to energy production

How many watts does your favorite car produce?


How many watts can
you produce?


How can you figure it out?

Time how long it takes to do a certain amount of work.


Do activity: Do you have more horsepower than a lawn mower?



9


Running up the stairs
: The work performed is the force of gravity on yourself
multiplied by the vertical height of the stairs. Measu
re the height of one
step and then multiply by the number of steps on the stairs to get the
vertical height.


H = ____________ m



Total height = __________ m


Measure the time you took to perform the work to calculate the power in your
body:



t =
____________ s


Measure your weight = ___________ lbs. = _____________ N


Calculate your power:









10


1.

How much work is done on a 100 N rock that you carry horizontally across
a 10 m room?


No work. Y
ou’re not changing its energy state.

2.

How much work is done on a 100 N rock that you lift in the air a
distance of 10 m?


W = F d = 100N (10m) = 1000J

3.

What would be the power you develop if you lifted the rock from #2 in a
time of 10 seconds?


P = 1000J
/

1
0s = 100 W

4.

If you lifted the previous rock twice as fast, how much power would you
need to develop?


200 W, twice as fast means, ½ the time, twice the power

Assignment Ch. 9
:
1
-
5, 33
-
37, 44




11


When the shotput is on the ground how much energy does it have?

None. Can’t do work.

How do you give

it energy?

Do some work lifting it or pushing it.

How do you know it has gained energy?

It can do damage, i.e. work, when it collides.

Demo: shotput on cinderblock

Work
-
Energy Theorem



the work done on a system is equal to the change in
energy of the sys
tem.




Work is a vector and has a direction associated with it!



When force is in the same direction as the distance covered:

Positive work means an increase in energy.


Ex. when you press the gas pedal in a car



When force is in the opposite direction as th
e distance covered:

Negative work means a decrease in energy, or a release of energy.

Ex. a car coming to a stop


1.

Kinetic Energy



(KE)


(units =
Joules
)
-

energy of motion


KE = ½ m v
2


2.

Potential Energy



(PE)

(units =
Joules
)
-

energy due to position,
stored energy.

(Gravitational) PE = m g h



Gravitational potential energy


stored energy due to height

When combined
in the work
-
energy equation:

W = KE + PE


12


1.

In the demonstration of lifting a 5 kg shotput 3 m in the air, it
required how much work?


W = PE = m g h = 5 (10) 3 = 150 J

2.

What is its change in potential energy?

150 J

3.

If the shotput was then dropped, how much kinetic energy would it
possess right

before it strikes the cinderblock?

150 J

4.

How fast was it going right before it struck the cinderblock?

KE = ½ m v
2

= ½

5 v
2

= 150 J : v = 7.75 m/s


5.

How much kinetic energy does the shotput have half
-
way down?

½ KE = 75 J

6.

How fast is the shotput

going half
-
way down? Explain why.

75 J = ½ 5 v
2

: v = 5.48 m/s


7.

What happens to the energy of the shotput when it hits the cinderblock?

It is turned into the KE of the cinderblock pieces, but eventually it goes
into heat.

Assignment Ch.
9
: 6,7,
38
-
42




13


What will happen to the student when the pendulum is released?

Nothing.

Demo: pendulum and student

Why does it do this?

The pendulum doesn’t have enough energy to get back to
its original height.

Energy is lost due to friction with the air.


Law of Conservation of Energy


energy cannot be created nor destroyed, only
transformed from one form into another, where heat is lo
west form.



The total energy before is equal to the total after.


Identify the two kinds of energy as it applies to the energy transformations
in the following examples:


1.

PE

2.

PE + KE

3.

KE

4.

KE + PE

5.

PE


Identify the points on the “roller coaster” that have max./ min. kinetic
and max./ min. potential energies. How do you know their locations?







Demo: match box cars and track

Why, in

general, are the successive hills on a rollercoaster lower than the
previous hill?

Energy is lost due to heat and can’t get back to original
height


14

Why does the car stop at the end of the “roller coaster?”

All of the energy was lost.

Where does the initial energy of the coaster go?

It turned into heat.


Heat



waste energy due to energy conversions and friction.


Can we ever get that energy back?

No. it is lost forever into space.

What determines the max. speed of a rollercoaster?

Th
e initial height of the coaster.


Can you calculate it out? How? (remember
gravity is accelerating the

rollercoaster and that mass doesn’t matter)

By the conversion of PE into KE at the bottom of the first hill


it is mass
independent due to gravity.



1.

The vertical drop of a rollercoaster is equal to a distance of 100 m.
What is the coaster’s speed at the bottom of the hill?


PE = KE,
m

(10) 100m = ½
m

v
2


10 (100) = ½ v
2
: v = 44.7 m/s ~ 100 mph



15

2.

An archer puts a 0.3
kg arrow to a bowstring. An average force of 200 N
is exerted to draw the bow string back a distance of 0.7 m.

a.

How much energy is being stored in the bowstring?

W = PE = 200 N (0.7m) = 140 J



b.

Assuming all of the energy goes into the arrow, with what speed

does the arrow leave the bow?

PE = KE = 140 J = ½ (0.3) v
2

: v = 30.6 m/s


c.

If the arrow is shot straight up, how high will the arrow rise?

PE = PE = 140 J = 0.3 (10) h : h = 47 m


Do lab: Conservation of Energy

Assignment Ch.
9: 8
-
11, 13, 51, 54




16


To demonstrate the conservation of energy through projectile motion








PE =


KE

The amount of PE of a matchbox car at the top of the race track is equal to
the tot
al amount of KE at the bottom of the race track. By measuring the
initial PE of the matchbox car, one can calculate the KE and hence the
velocity of the matchbox car, and predict the range of the car using
projectile motion equations.








h






















x




Using a matchbox track, set
-
up a ramp on a lab table as shown. A matchbox car
will be used as the projectile since its mass is large compared to the number
of moving

parts
-

this will reduce rotational inertia and friction
-

and will
give a more accurate prediction.


Mark a starting position at the top of the track using your pencil and
measure the height of this position relative to the table top. This will be
used
to calculate the initial PE of your matchbox car and ultimately it will
determine the velocity the car will travel off the table top. Be sure to
position the track at a height where the matchbox car will not hit the
cabinets, or position the track away fro
m the cabinets.

1.

Using the conservation of energy equation, calculate the speed with
which the matchbox car leaves the table top horizontally.

Height of starting position = ____________ m


17



PE =



KE


m g h = 1/2 m v
2

What drops out of the equation? Does
that make sense?





Calculated speed = ______________ m/s

2.

Roll the matchbox car down the ramp 8 times and create a table of range
values and average range.

Trial

Range

1


2


3


4


5


6


7


8


Average Range =



3.

Calculate the average speed of your

car by dividing your average range
by the time spent in the air = 0.43 seconds.







18

4.

Do an error analysis to see how close you were to your predicted speed.


% Error =
|(actual
-

theoretical)|








theoretical



1.

Describe what happens to

the kinetic energy of the matchbox car as it
rolls down the ramp.



2.

Describe what happens to the potential energy of the matchbox car as it
rolls down the ramp.



3.

How close were you to the actual speed?



4.

What were some of the factors that influenced the
matchbox car and its
speed?




5.

Would the matchbox car ever have a speed greater than what you
predicted?




6.

Given the experiment, do you think that the energy of the matchbox car
is being conserved? What other form of energy is involved between the
car and

the track that would change the car’s energy but not the total
energy?




19


Cranes are a compound machine. That is, they are composed of more than one
simple machine. What exactly is a machine?


Machine


a device that changes the force and/or

direction of a force

Neglecting
friction a machine can be 100% efficient

therefore:

work input = work output




F
in

x distance
in

= F
out

x distance
out


Work



force acting parallel through a distance that changes the energy of an
object

Mechanical Advantage (MA)


a ratio that describes
how much a force is
multiplied.


MA = F
out
/ F
in

3 Simple Machines:

1.

Lever



a machine composed of a rigid bar that will rotate about a fixed
axis.

*
MA = d
in

/ d
out



Lever arm


the distance the input force is to the fulcrum



Most efficient machine

Fulcrum



the fixed axis of rotation or hinge


o

1
st

class lever


fulcrum is between input

and output forces

ex. teeter
-
totter, pliers

o

2
nd

class lever


output force is

between the fulcrum and input

ex. wheel barrow, nut cracker

o

3
rd

class lever


input force is

between the fulcrum and output force

ex. boom crane, your arms and legs




20

2.

Pulley


rotating lever that uses ropes or

cables to change the direction of a force, or

with a system of pulleys can multiply forces










MA = 5



MA for a pulley is simply found by counting the number of ropes pulling
up on the weight!


3.

Inclined Plane



(ramp or screw)
-

a machine that increases input
distance to decrease input force
. A screw is a ramp wrapped

around

a shaft.








The MA for a
ramp can be found

by dividing the ramp length by rise or

height of the ramp.

o

For a screw it is called pitch

1.

A student pushes down on a lever with a force of 10 N a distance of 1m.
How high
will an 80 N rock be raised? What is the MA for this machine?

1/8 m, MA = 8



2.

Your arm is a 3
rd

class lever. The MA is about 0.2. If you lift a 30N
weight, how much force is your biceps muscle pulling on your forearm?

MA =
F
out

/

F
in

0.2 = 30 N / F
in
;

30 N /0.2 = 150 N



21

3.

MA for a lever can be described as the ratio of length from the fulcrum.
If your input force is 5 m from the fulcrum, and the output force is 1 m
from the fulcrum, what would be the MA for this lever?

MA = 5

4.

What is the MA for a pulley
when you apply a force of 150 N to pull up
on

a 900 N weight? How many ropes are pulling up on the weight?

MA = 900 / 150 = 6


5.

A force of 40 N is used to push an object up a ramp a length of 2.5

m.
The height of the ramp is 1 m. What is the ramp’s MA? What

is the
object’s weight?

MA = 2.5 m / 1 m = 2.5 : MA (F
in
) = F
out

= 100 N


6.

If a block of ice is pushed up a smooth incline a distance of 6 m, to
lift it a vertical distance of 1 m.

a.

What is the ramp’s mechanical advantage?

MA = 6

b.

If the block weighs 300 N,

how much force w
ould be required to
push it up
the ramp?

F
in

= 50 N

c.

How much work was done on the block of ice pushing it up the ramp?

W = F d = 50 N (6 m) = 300 J


d.

How much potential energy will the block have at the top of the
ramp?

PE = mgh = 300 N (1
m) = 300 J


e.

Compare the answers to c and d, what do you see? Explain your
answer.

They are the same, because work input = work output

f.

If the block of ice were to accidentally slide down the ramp, how
much KE would the block have?

PE = KE, it would have 300

J of KE


22

g.

How fast will the block of ice be traveling at the bottom of the
ramp?

KE = ½ m v
2

: 300 = ½ 30 kg (v
2
); v = 4.47 m/s

7.

Use the diagram at the right to answer the following questions:

a.

What is the mechanical advantage of the
pulley system?

MA = 5

b.

If

the crate weighs 1000 N, how much force
will be required to lift the crate?

F
in

= 200 N


c.

If you pull down on your end of the rope a distance of 50 cm, how
high will the crate be lifted?

H = 10 cm


d.

If you do 5000 J of work to lift the crate, how much poten
tial
energy will the crate possess?

PE = 5000J

e.

How high is the crate when you did the 5000 J of work?

PE = mgh = 5000J = 1000 N (h); h = 5 m


Assignment Ch.
9: 15
-
18, 47




23

What is the efficiency of your car?

Only about 30% efficient
, it is also a heat engine


discussed later.

What does
efficiency mean?

Efficiency


is a

ratio, expressed as a percent,
that relates the amount of
actual work output to the actual work input.


Where does this energy difference go?

Heat

due to energy conversions and friction.

Is it possible for machines to be

100% efficient? What causes the efficiency
of a machine to go down?

Machines will always be less than 100% efficient due to friction.

If a machine is 100% efficient, then all of the work input = work output.


Eff. = AMA / IMA =

Actual Mechanical Advantag
e





Ideal Mechanical Advantage

= W
out

/ W
in

=

I deal i nput f orce




A ctual i nput f orce

What is the efficiency of a textbook sliding on a ramp?





1.

A child on a sled with a total weight of 500 N is pulled up a 10 m slope
that elevates her a vert
ical distance of 1m.

a.

What is the ideal mechanical advantage of the slope?

IMA = 10

b.

If the slope is without friction, and she is pulled up the slope
at a constant speed, what will be the tension in the rope?

F
in

= 50 N

c.

If the slope has friction, and the
rope tension was 100 N. What is
the actual mechanical advantage?

AMA = 5


24

d.

What would be the efficiency of the slope that has friction?

Eff. = AMA / IMA = 5/10 = 0.5
or 50%


e.

If a sled with a total weight of 800 N was to be pulled up the
slope, what force wou
ld be needed if friction were present?

AMA = 5; F
in

= 160 N


2.

A pulley is set up so that 4 ropes are pulling up on a piano. The piano
weighs 1000 N.

a.

What is the ideal mechanical advantage of this pulley system?

IMA = 4

b.

If it were a frictionless pulley, how
much force would be
necessary to lift the piano?

F
in

= 250 N


c.

If friction is present, and it actually took 300 N of force to
lift the piano, what would be the actual mechanical advantage?

AMA = 3 1/3


d.

What would be the efficiency of the pulley with
friction present?

Eff. = 3 1/3 / 4 = 0.83 or 83%


Assignment Ch.
9: 19
-
21




25




Write down key terms with their definitions for each chapter.




Write down the equations used in each chapter.




Solve the following example questions:

1.

Work is required to lift a heavy barbell. How many
times more work is
necessary to lift it 3 times as high?


2.

If a barbell weighs 120 N, and it is lifted a distance of 2 m, how much
work was required? If it were lifted a distance of 6m?



3.

What if lifting the barbell in #2 was done in a time of 3s, how much

power was developed in both cases?


4.

A 50 kg object has a velocity of 10m/s, what is it’s kinetic energy?



5.

If the previous object is traveling twice as fast, how much kinetic
energy will it possess? Three times as fast?


6.

A 10 kg rock on the edge of a 100
m cliff has how much potential energy?
If it were to fall, how much kinetic energy will it have right before it
strikes the ground? How fast will it be traveling?





7.

In what two ways can a machine alter an input force?





26

8.

What is the mechanical advantage
of a machine that applies a force of
800N when a force of 80 N is applied to lift a heavy weight? If an input
distance of 1m was applied to the machine, how high was the weight
lifted?





9.

What is the relationship between the MA and the ropes on a pulley?


10.


What is the mechanical advantage of a ramp that is 10m long that
has a vertical distance of 2m?


11.


What would the amount of force required to lift a 500 N object
using the ramp in #10? Assume there is not friction.



12.


If friction were present in the ramp from the previous example
and it required 150 N of force to push it up the ramp, what is the
efficiency of the ramp?




13.

If a worker uses a pulley to lift a 5000N piano and notes that for
every 2 m of rope he pulls down

the piano is lifted 0.1m. What is the
ideal mechanical advantage of this machine? How many ropes are pulling
up on the piano? How much force did the worker apply to lift the piano?
If it actually required an input force of 300N, what is the machines’
effi
ciency?




27







Chapter
10

Highlights:





Rotation and Revolution





Centripetal Force















Key Terms









Rotation

Revolution

Linear Speed

Rotational Speed

Centripetal Force

Tangential Speed

Centripetal Acceleration

Artificial Gravity




28


How do the planets move around the sun? Did you know that the earth is
travelin
g at a speed of about
67,
000 mph
? Where is it going?

In a circular orbit. Nowhere, it is trapped b
y gravity in a circle.


What is circular motion?

Movement around an axis.

What are the components of a circle?

Radius




distance from the axis to the edge of



the circle

Diameter


distance across a circle = 2r

Axis



center of the circle of rotation

Circumference



distance around a circle = 2

r



To have constant circular motion, what must you have?

o

Constant _
Radius
_

o

Constant _
rotational speed
_

There are two kinds of circular motion, what’s the difference?

Rotation



movement about an axis inside of
itself

ex. The earth rotates about its axis.


Revolution



movement about an axis outside itself

ex
. The earth revolves around the sun.


A merry
-
go
-
round
rotates

about its axis, while you
revolve

about its axis.

Demo: student on turntable

Linear speed



distance covered per unit time



Rotational Speed



(angular speed)
-

how fast something spins about an axis.



w = 2


rotations/time



29

Tangential Speed



linear speed but
around a circle


Demo: rubber stopper on string

v
T

= r x w



Where r is the radius of the circle or curve and w is the rotational
speed.



It can also be found by taking the circumference divided by the time.


1.

How fast is this rubber stopper going around my head?




2.

How fast is the student rotating on the
platform? With arms extended,
how fast are the fingers going versus the shoulder? Why?




3.

What happens to the rotational speed when the rotating student brings
the hand weights in toward the axis? Why does this occur?

Rotational speed increases. The speed of the mass wants to stay moving at the
same tangential speed, Newtons 1
st

law, but the radius is now smaller,
therefore the number of rotations per unit time increases.



1.

Which part of the earth’s surface has the greatest rotational speed?
Which part has the greatest tangential speed?


They all have the
same rotational speed. The equator has the largest radius,
and as a result, has the largest tangential speed.



30

2.

On the merry
-
go
-
round at Six Flags, the horses at the outer edge are 3
times farther than the ones toward the center. If you sat on the center
ho
rses you would experience 0.4 RPM and a tangential velocity of 2 m/s.
What will be the rotational and tangential velocity of the outer horse/

Rotational is 0.4 RPM, and 6 m/s tangential speed


3.

Trains ride on tracks that are equidistant. When a track goes a
round a
curve, which track is actually longer than the other, the inner track,
or the outer track? When a train goes around a curve, which part of the
train are you actually traveling faster, the inner or the outer part of
the train?

The outer track, it ha
s to travel farther in the same amount of time. The
outer train, moving about in a train going around a curve can sometimes
challenge your balance!


Assignment Ch.
10:1
-
7, 29, 31, 33




31


What happens when you swing a penny balanced on hangar?

Nothing. It stays on.

What happens when you swing water in pan around your head?

Nothing. The water stays in.

What keeps the rubber stopper in circular motion?

The string creates a te
nsion force.

What keeps your car in a curve when you turn?

Friction.

Why do all of these work the way they do?

They are all acted on by a centripetal force.

Centripetal Force



(F
C
)
force that causes circular motion.

It is a force
that acts perpendicular to the velocity of an object towards the axis of the
circle.

F
C

=
m a
c



Assumed to be constant circular motion

o

Constant speed in a circle

o

Constant radius



Center of a circle is called the _
axis
___.



This force is directl
y toward the center of rotation.

Centrifugal Force



a “circular” force that pushes objects outward but is
based on the object’s inertia.



Fictitious force



It exists from the
observer’s inertia

Centripetal Acceleration



(a
C
)
the rate of change of

direction per unit time.



Recall the definition of acceleration:



Depends on two things:

o

1.
speed

o

2.
radius

Applying this to circular motion:

a
c

= v
2

/ r




32

NASA is presently working
on a space craft that will be able to transport
astronauts to Mars. The trip itself will take months. After such a long time
in space without gravity, the astronauts’ bones and muscles will be too weak
to land safely on Mars. How would NASA be able to simu
late gravity so the
astronauts could survive?

Use a centripetal force

What must the centripetal acceleration be equal to?

10 m/s
2

to simulate gravity’s acceleration

Calculate the tangential speed of a space station if the station has a radius
of 100 m.



v = 31.6 m/s

Videos: space station video clips

Assignment Ch.
10:

8
-
14, 36, 39, 42, 43








33











Chapter
2
1

Highlights
:





Measuring Temperature





Heat





Specific Heat





The High Specific Heat of Water





Thermal Expansion




Key Terms













Temperature

Fahrenheit

Celsius

Kelvin

Kinetic Energy

Heat

Absolute Zero

Thermal Equilibrium

Thermal Energy

Calorie

Thermal Expansion

Specific Heat


34


How do you know if it will be a nice day outside or not?

Usually by its temperature.

How can
you tell if you are sick?

Temperature

How do you know your food is cooked properly?

Temperature

Temperature


(everyday definition)


how hot or cold something is.


Temperature is
scientifically determined by:

1.


The type of molecules


certain molecular structures can store more
energy than others and can vibrate in more than one direction.


2.


Mass of the molecules



more mass at a particular speed results in more
energy.


3.


Speed of t
he molecules

-

faster moving results in a higher temp.



Temperature


(scientific)


is

the average KE of the molecules



Kinetic Energy (KE)

energy of motion, determined by mass and speed.





as molecular motion increases:

temp. increases




atomic

MASH pit:

the more violent the atomic collisions the higher the
temp. and the material will expand.



use for thermometers


mercury or alcohol expands at higher temp.

the
expansion

is an indicator of the energy the material possesses




35

Temperature Scales:

Celsius



based on the freezing and boiling pt. of water, where 0
o
C water
freezes or melts, 100
o
C water boils or condenses.


Fahrenheit


based on the freezing pt. of salt water (ocean water) 0
o
F, and
human body temp. 98.6
o
F



Kelvin

(SI unit of temperatu
re)


uses the Celsius scale but without
negative numbers. Predicts an absolute zero temp.


F = 1.8C + 32
o

K = C + 273

Temperatures of freezing water, and boiling water on the different scales:


Freezing
water

Boiling
water

C

0

100

F

32

212

K

273

373


Absolute Zero



the universal lowest temp. predicted by Kelvin in which all
molecular motion stops, can never be attained

but have come extremely close.


-
273
o
C,
-
460
o
F, 0K


Convert today’s temperature to Celsius and Kelvin.





Convert 40
o
C to Fahrenheit
and Kelvin.

104
o
F, 313 K



36


Which of the following will increase a bucket of room temperature water the
most? Why?

a.

A small beaker of boiling water

b.

A

large beaker of 50
o
C water

Even though the small beaker of water is at a higher temp., the large beaker
had more thermal energy.

Heat


(units =
calories (joules)
)
-

the flow of thermal energy from one
object to another.




Heat flows from _
high temp
_ to _
low temp
_.

Thermal Energy


(units =
Joules
)
-

total internal KE of the molecules





Heat is the result of the release of thermal energy

What quantities determine the internal energy of a substance?

1.

Temperature


average KE of the molecules in a substance



2.


Mass


more mass at a given temp. will have more energy



3.


Type of material


some molecules can store more energy than others


related to the specific heat of a substance.


Thermal Equilibrium



when the flow of heat stops


occurs when substances
are
at the same temp. (
NOT

the same internal energy)


How do you measure the heat?

Measure the gain in energy of a known substance (water) for comparison to
other substances.




37

Listed in Nutritional Information on various products:

1 Cal. = 1000 cal

1 cal = 4
.184 J

calorie



unit of energy gained by 1 gram of water to
increase its temp. by 1
o
C.

Questions:

1.

A certain amount of energy is given to a heating
plate and it raises 1L of water 2
o
C. What would the
same amount of energy do to the temperature of 2L
of
water?

1
o
C


2.

Room temperature is about 70
o
F. What would be room
temperature in Celsius and Kelvin?

21
o
C, 294 K


3.

A thermometer is in a container half
-
filled with 20
o
C tap water. What
will be the water’s temperature after the following:

a.

An equal amount of 40
o
C water is added to this beaker.

30
o
C

b.

An equal amount of 0
o
C water is added to this beaker.

10
o
C

c.

An equal amount of 100
o
C water is added to this beaker.

60
o
C

True or False.

A red hot piece of metal is added to a bucket of cool water.

a.

The decrease in
temperature of the metal is equal to the increase in
temperature of the water.

F

b.

The quantity of heat added to the water is equal to the quantity of heat
lost by the metal.

T

c.

The metal and the water will become the same temperature.

T

d.

The final temperature

of the metal and water is halfway between the
initial temperatures of each.

F

Assignment Ch. 21:
1
-
10, 56


38


What determines the amount of thermal energy contained in an object?

1.


Temp.

2.


mass

3.


Type of material

Heat


(uni
ts =
calories
)


(“Q” in the equation)



flow of thermal energy


Specific Heat Capacity



(units =
cal/g
o
C
)


(“c”in the equation)


relates the amount of energy gained or lost per unit mass of a certain
material.


Water’s sp. Heat = 1 cal/g
o
C








|





|

Where:

Q =

heat exchanged in calories



m =

mass of the substance



c =

specific heat of the substance



T
f

=

final temp. of the substance



T
i

=

initial or beginning temp. of the substance


Examples:

1.

Heat was added to 100 mL of water raising its

temperature from 20
o
C to
30
o
C. How many calories of heat were

added to the water?

Q = 100g (1) (30
-
20) = 1000 cal


2.

A 200g piece of iron is placed into 300 mL of 20
o
C water. The water’s
temperature increases to 25
o
C. The spec. ht. of iron is 0.11. What was

the initial temperature of the iron?

Q
iron

= Q
water

: 200 (0.11) |(25


T
i
)| = 300g (1) (25


20)





22 |(25
-

T
i
)| = 300(5)





22|25
-

T
i
| = 1500





|25
-

T
i
| = 68.2
o






T
i

= 93.2
o
C

Assignment Ch. 21:
11
-
13, 22
-
28


39


Why does water have such a high specific heat?

It has strong molecular bonds.


What are
the bonds that hold water together?

Covalent, and hydrogen bonds




Remember, specific heat is comparing energy per unit mass


stronger
bonds means more energy required to pull them
apart.

What are some uses for water because of its high specific heat?

Extinguishing fires

Heating and cooling homes

Cooking



Additives can change water’s specific heat:

o

Anti
-
freeze


increases the specific heat which makes water boil
at higher temps.

Does the high specific heat of water affect the climate and weather of cities
near large bodies of water?

Yes. It makes it more temperate


less temp. extremes.


Which would
have a higher specific heat: water or land?

Water

Which one would heat up faster in direct sunlight?

Land

Which one would cool down slower at night?

Water

In the summer time, what happens to the wind in Milwaukee at night? During
the day?

It shifts. Wind b
lows out to the lake at night


air above water is higher
temp.


land has cooled off quicker. Wind blows inland


air above the land
is higher temp. due to sunlight heating it up rapidly.

In the winter time, what happens when the wind blows across Lake
Michigan?

It takes the warmer moister air from the lake and creates
lake
-
effect snow

when it reaches the colder, freezing air above land.





40

What about the seasons? The
peak sunlight,
the largest amount of sun energy
occurs in late June, yet the highest temperature days don’t occur until
August. Why are the seasons delayed approx. 1 ½ months from the peak
solstices?

It takes some time for the land to cool off enough, or w
arm up enough to
reach peak temps.

Why does England have mild temperatures all year long, and then at night get
thick fog?

It is surrounded by water which stays at roughly the same temp. all year
long.



41


What happens when the brass ring is heated and place
d

over the ball?

The ring didn’t fit before and

now it does


the heat caused it to expand.

Demo: ball and ring

Does this work for all substances?

For most substances, when heated causes the material to expand. There are a
few exceptions.


Thermal Expansion



the volume of a substance increases when heated due to
the KE of the molecules increasing. The KE of the molecules collide more
frequently and violently as to cause the space between the molecules to grow.



MASH pit of molecules



Expansion rates:

o

Gases exp
and the most


lowest sp. Heat

o

The lower the sp. Heat the higher the expansion rate

Applications:



Thermometers



Expansion joints in bridges and buildings



Rubber filled grooves in asphalt roads and concrete sections in
sidewalks



Sagging telephone lines



Shrink fitting
,
Induction shrink fitting



Bimetallic strips

Bimetallic Strips



welded brass and iron


thermostat



when heated the
different materials expand at different rates.

Water is an exception to the expansion rule due to its open
crystalline
structure:



As water cools down to 4
o
C it _
Shrinks
_.



As water continues to cool to 0
o
C it _
Expands
__.



As
solid
water continues to
cool below 0
o
C it
__
Shrinks slightly
__.

Why can you fish in the winter? Why don’t the fish
die?

Warmer water (4
o
C)

sinks due to it being more
dense than ice.

Assignment Ch. 21:
15
-
20, 41
-
45



42







Chapter 2
2

Highlights:




Conduction, Convection, and Radiation




Newton’s Law of Cooling




Evaporation









Key Terms





Conductor

Insulator

Heat

Newton’s Law of
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43


Everyone has probably had a Poptart from the toaster. Specifically, what is
going on when yo
u are toasting your Poptart?

It is heating up through the 3 methods of heat transfer.

Demo:
P
optarts

Physically how is the toaster heating up your poptart?

1.

Conduction


transfer of thermal energy through contact between
materials


conductors
vs.

insulators.

2.

Convection



transfer of thermal energy through the movement of a fluid
such as air or water.

Hot air rises because it is less dense carrying
away thermal energy as it rises.

3.

Radiation



energy is transmitted by Infrared light


electromagnet
ic
waves which we call heat in common language.

(heat lamp)

When you touch the Poptart when it is done, it is __
HOT
_! Why?

The thermal
energy was transferred by conduction to your hand by the crust.


When you let it stand for a few seconds and eat the
Poptart
,

the crust is
_
cool
_.

While the filling inside is _
hot
_____. Why does this occur?

The crust
was cooled by radiation and convection. It also has a low specific heat,
which means it will cool quickly. The filling can only cool by conduction to
the cr
ust
-

which is an insulator, and it has a very high specific heat so it
will retain its thermal energy.

Conductor


transmits thermal energy easily due to its loosely bound outer
electrons. The electrons will allow IR light to transmit through.



Heat
conduction can also be felt by touch:



Grab onto a conductor at room temperature. It feels __
cold
__. Why?


T
he metal is at a lower temp. the
n your hand and it will cause the heat to
flow more rapidly from your hand to the metal. The flow of heat out of your

hand is interpreted as cold.

Insulator



doesn’t transmit thermal energy well and will keep the thermal
energy localized.



Example: glass with torch


44



Place your hand on an insulator type material vs. the conductor at room
temperature. It feels _
warm
____.
Why?

Even though the paper is at the
same temp. as the metal, it will only transfer a small amount of thermal
energy per unit time.


1.

If you hold one end of a metal bar against a piece of ice, the

end in
your hand will soon become cold. Does cold flow from the ice to your
hand?

No. The heat from your hand is going into the ice.



2.

Wood is a better insulator than glass. Yet fiberglass is commonly used
to insulate wooden buildings. Why?

The air pocket
s trapped by the fiberglass create a better insulation than the
wood.

3.

You can stick your hand into a hot pizza oven for several seconds
without harm, whereas you’d never touch the metal insides for even a
second. Why?

The transfer of heat from the hot air
to your hand is very low due to the low
spec. heat of the air and it is an insulator. Metal is a very good conductor
of heat and will transfer almost immediately.

4.

You can hold your fingers beside the candle flame without harm, but not
above the flame. Why?

The heat one gets from holding fingers on the side is IR light. Most of the
thermal energy is carried away by convection.


Assignment Ch. 22:

1
-
5, 10, 22, 23, 26




45


Which one will cool off faster a hot cup of coffee left on a counter
-
top or
one placed in a

freezer? Why?

The one in the freezer. There is a larger temp. difference between the
freezer and the cup of coffee.


Newton’s Law of Cooling



(or warming)


the rate of cooling is proportional
to the difference in the temp. of the objects.




Heat flow is
proportional to ____
temperature
________.

o

Increased rate of cooling is due to a ___
larger temp. diff.
_____.

o

Decreased rate of cooling is due to a ___
smaller temp. diff.
___.

Why does this happen?

Energy always flows from high to low.


Heat



energy flow fro
m high temp. to low temp.


Evaporation


(condensation is opposite)


cooling process which allows the
higher than average temp. molecules to escape, thereby carrying away more
than their fair share of energy.

Water/Alcohol on skin


How does it feel? Why?


Cold due to the alcohol extracting heat from your hand to evaporate.

What can you conclude about evaporative processes?

It is a cooling process.

Why does this happen?

I takes thermal energy from its surroundings in order to turn into a gas.

Demo:
molecules in a jar

Graph of molecular temperatures:



# of molecules


0


Temp. (K)


46

Does Color have an effect on the rate of cooling and absorption of energy?

Yes. Black absorbs/radiates more heat than white or silver.

Demo:

lamp on colored cans

Questions:

1.

If a good absorber of radiant energy were a poor emitter, how would its
temperature compare with its surroundings?

It would always feel cold


constantly absorbing energy.


2.

Is it more efficient to paint a
heating radiator black or silver?

Black,

it gives off more energy.


3.

Why is it a good idea to keep hot beverages covered?

It stops the cooling by evaporation.


4.

Why do thermos bottles have a silver coated, vacuumed interior?

The silver reflects the IR light back in and the vacuum is a perfect
insu
lator. No molecules to conduct the heat.


Do Coffee Lab

Assignment Ch. 22: 12
-
17, 33


47



Chapter 22, problem #34;

Suppose

that a person at a restaurant is served coffee before he
or she is ready to drink it. In order that the coffee be hottest when the person is ready
for it, should cream and sugar be added to it right away or just before it is drunk?


Predict what you think

is the answer to this problem using the effects of temperature
difference, color, specific heat, and evaporation on the rate of cooling:







Direct measurement of the problem:

Pour
an amount of coffee into two
Styrofoam cups up to the line indentation toward the top of the cups. Immediately add two
sugar packets and one creamer to one of the coffees, stir, and measure the initial
temperatures of both coffees. With a stopwatch, time 8

minutes, and record the
temperatures of both coffees at one minute intervals. At the end of 5 minutes, add the
cream and sugar to the other coffee, and record the temperatures.

Time

Coffee w/cream and sugar

Coffee w/o cream and
sugar

0



1



2



3



4



5




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6



7



8




48

Does color influence the rate of
cooling more in the coffee?
Pour an
amount of coffee into a Styrofoam cup up to the line indentation toward the top of the
cup. Pour an equal amount of hot water at the same temperature in another cup. Measure the
initial temperatures of both cups. With a
stopwatch, time 8 minutes, and record the
temperatures of both cups at one minute intervals.

Time

Coffee

Hot water

0



1



2



3



4



5



6



7



8




Does the sugar influence the rate of cooling more?

Pour an amount of hot water into two Styrofoam cu
ps up to the line indentation toward the
top of the cups. Add two packets of sugar to one of the cups of hot water. Measure the
initial temperatures of both cups. With a stopwatch, time 8 minutes, and record the
temperatures of both cups at one minute int
ervals. At the end of 5 minutes, add two
packets of sugar to the other cup, and record the temperatures.

Time

Hot water w/sugar

Hot water

0



1



2



3



4



5




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6



7



8




49

Does the creamer influence the ra
te of cooling more?

Pour an amount of hot water into two Styrofoam cups up to the line indentation toward the
top of the cups. Add a container of creamer to one of the cups of hot water. Measure the
initial temperatures of both cups. With a stopwatch, tim
e 8 minutes, and record the
temperatures of both cups at one minute intervals. At the end of 5 minutes, add the
creamer
to the other
cup, and record the temperatures.

Time

Hot water w/creamer

Hot water

0



1



2



3



4



5




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6



7



8




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50








Chapter
24

Highlights:




First Law of
Thermodynamics




Second Law of Thermodynamics




Carnot Heat Engines









Key Terms












Thermodynamics

First Law of Thermodynamics

Adiabatic

Second Law of Thermodynamics

Heat

Pressure

Heat Engine

Work

Entropy



51

How does a
Diesel engine work
?

The heat of compression ignites the fuel air mixture.

What happens to the temperat
ure of air when you compress it?

It heats up.

Demo:

bike pump, air compressor

Why does this occur?

The molecules are forced into a smaller volume causing more violent
collisions with the container and each other.

Demo: bouncing ping
-
pong ball

Where does
this energy come from?

Came from the work done compressing the gas.


Would it be equal to the amount of energy we put into compressing it?

Yes. But there is some from the friction of the pump.


Does this process work in reverse? What happens when we expand

a gas?

Yes. The sudden expansion causes the temp. to go down.

Less violent and less
frequent collisions with an increased space between the molecules causes an
overall lower temp.

Demo: compressed air on hands

Thermodynamics



study of the flow of heat.


First Law of Thermodynamics



(law of conservation of energy)


the heat
added to a system is equal to the energy increase of the system, including
any work done by the system.




Compression __
increases
_ the temp. of
a gas.



Expansion ___
decreases
___ the temp. of a gas.

By ideal gas law: PV = nRT and increase in temp. for a given volume will
increase the pressure. If the container has a moveable piston or some
thing
similar, the gas will be allowed to expand and do work.


Work



(J)
-

a force acting
through a distance that changes the energy of a
system.

Heat Engines



a machine that converts heat into mechanical energy




52

Heat added = Heat output + Work done

Adiabatic Process



an isolated system that does not allow heat to be removed
or added that ch
anges the pressure and volume of the system. PV = energy of
the system.

Explanation of an adiabatic heat engine process:



2


1

Temp./Pressure

3


4




Volume

1.

An explosion superheats the gas
es inside an engine, creating a

sudden
increase in
temp./
pressure.

2.

The in
crease in pressure moves a piston. As the piston moves, the volume
increases, and the pressure and temperature decrease. The exhaust is
released.

3.

The piston
allows

in air and gas

by decreasing pressure and temperature.

4.

The piston does work
compressing the air and gas to a higher pressure
and temperature.



The area under the Pressure/Volume curve is the available energy to do
work


the larger the area = more work.


This process works in reverse = Refrigeration cycle. If you do work
decreasing

the pressure of a gas by expanding it, it will decrease its
temperature.

external work done = decrease in internal energy



This does not violate the conservation of energy due to more work being
done than a decrease in internal energy.


How does this
process apply to weather and climatic conditions?

Differences in temp. drive weather patterns and wind due to the flow of heat.

What happens to the atmospheric pressure as you increase height in the
atmosphere?

It decreases.



53

If you had a balloon filled wi
th helium and let it rise in the air, what
would happen to the size of the balloon?

It would expand and get bigger.

What happens when you expand a gas?

It cools.

Apply this principle to rising air currents with water vapor:






Assignment Ch. 24:
5
-
12, 3
3
-
36




54


How many different kinds of engines are there?

Dozens.

What basic principles do they use?

Compres
s an air fuel mixture. Ignite it. Control the expansion to do work.

Demo: engine animations

Second Law of Thermodynamics


Heat always flows from High temp. to

low temp.,
energy goes from a higher state to a lower state.




The amount of work from a high temp. source to a low temp. source can
never be 100%


Heat Engines



a machine that converts the flow of thermal energy into
mechanical energy


Demo: steam engine

High temp. source = __
steam = 100
o
C = 373 K
_


Low temp. source = ___
room temp. air = 20
o
C = 293 K
__


What
happened to the energy of the fuel source? Where did it end up? Can we
ever get the energy back?

It was burned and turned water into steam.
Some of t
he

energy
burned went
into

steam, but also into the exhaust.
But u
ltimately
the energy went
into
the work done and the heating up of the classroom. We can’t get it back
because the heat is radiated away into the surroundings.

What happens to the temp. of

the room?

Temp. went up.


Entropy



a measure of disorder of a system, related to the amount of
available energy and it is always decreasing



This will not happen due to the room (low temp. source) being very large
compared to the steam exhaust
-

a
s the
engine is run mor
e and more until the
room temperature
gets very hot, will you get as much power

from the steam
engine?

No. the temp. difference comes closer together until there is no flow of heat



55

Carnot Heat Engine



a theoretical frictionless engine t
hat can convert as
much thermal energy into work. It serves as an absolute upper limit to heat
engines.

Max. Eff. =
T
hot
-
T
cold


T
hot

What would be the maximum efficiency for the steam engine?

Eff. = (373
-
293)/ 373 =
.214 = 21.4%


There will always be heat energy lost due to heat to the cold source, there
can never be an engine that is 100% efficient. If a heat engine were 100%
efficient then all of the fuel that is burned will be converted into work. If
all of the energy is convert
ed into work, there will not be a need for a cold
source. If there is not a cold source, then what causes the heat to flow? If
there is no cause for the heat to flow, then the burning fuel cannot be
converted into work!



1.

What would be the max. eff for a car engine? High temp = 700K, low temp.
exhaust = 300 K.

Eff. = (700
-
300)/ 700 = 0.571 = 5
7.1%


2.

What reduces the efficiency of a heat engine?

Friction. Moving parts. Temp. of fuel burn.


3.

How could you increase

the efficiency of a heat engine?

Reduce friction. Reduce the number of moving parts. Increase the source temp.

Video: ceramic engines
,
gas turbine engine

4.

Would it be a good idea to cool your room by leaving the door to your
refrigerator open? Explain.

No. The temp. inside

the fridge is low but the back of the fridge gets very
hot!

5.

If 10 J of energy is added to a system that does no external work, how
much will the internal energy of that system be changed?

10 J

6.

If 10 J of energy is added to a system that does 4 J of external work,
how much will the internal energy of that system be raised?

6 J



56

7.

What is the max. eff. of an engine if the hot source and the cold source
are the same temperature = 400 K?

Eff. = (400


400)/400 = 0/400 = 0%

It won’t work.


8.

What is the max. eff. of an engine having a
hot source at 400 K and a
cold source at absolute zero = 0 K?

Eff. = (400


0)/400 = 400/400 = 100%

Absolute zero can never be attained by definition.


9.

What is the max. eff
. of an engine having a hot source at 800 K and a
cold source at 310 K?

Eff. = (800
-
310)/800 = 0.6125 = 61.25%

This is the absolute limit of efficiency for the internal combustion engine.
The push towards electric motors is
now stronger due to recent tech
nological
advances which make them up to 96% efficient. Electric motors are not heat
engines and are not constrained by the Carnot Engine Efficiency
model.

Assignment Ch. 24:

13
-
18, 26
-
29, 38
-
40, 51
-
58




57



Write down key terms with their definitions for each chapter.




Write down the equations used in each chapter.




Solve the following example questions:

1.

What is used to measure temperature?


2.

Convert 74 degrees
F, into Celsius, and Kelvin.



3.

Why is it incorrect to say that matter contains heat? What does it
contain?


4.

Do substances that normally heat up quickly have a high or low specific
heat?


5.

Compare the specific heat of water to other known substances, how doe
s
it compare? Why?



6.

Why does a bimetallic strip bend when heated or cooled?


7.

Which of these expand the most when heated: Solids, Liquids, Gases? Why?



8.

At what temperature is the density of water the greatest? Why?



9.

Calculate the number of heat calories
when 400g of water is heated from
20 degrees Celsius to 80 degrees.




10.

Calculate the number of heat calories lost by a 1200 g chunk of
copper metal, c = 0.2, as it cools from 100 degrees to 30 degrees.


58

11.

Calculate the specific heat of 600g of an unknown
substance when
it is cooled in 500ml of water. The initial temperature of the substance
is 100 degrees, and the initial temperature of the water is 23 degrees.
They both reach thermal equilibrium at 28 degrees.





12.


What is the role of loose electrons in h
eat conductors?


13.

What is radiant energy?


14.

What color is a good absorber of heat energy? What is a good
emitter?


15.

What will cool off faster, a cup of coffee that has the cream in
sugar added right away, or one in which you wait and then add the cream
and su
gar? Why does this work?



16.


What reduces the efficiency of a heat engine?


17.

If an engine is frictionless, is it 100% efficient?

18.

Explain the energy cycle for all heat engines.




19.

Calculate the max. efficiency

of an engine that operates between a
high temp. of 900 K and a low temp. of 300 K.





59






Chapter
25

Highlights:





Wave Description

Interference

Standing Waves





Doppler Effect and Shock Waves








Key Terms










Periodic Motion

Wave Pulse

Continuous Waves

Mechanical Wave

Transverse Wave

Longitudinal Wave

Electromagnetic Waves

Compression

Rarefaction

Wavelength

Period

Frequency

Wavespeed

Interference

Constructive

Destructive

Standing Wave

Node

Anti
-
Node

Doppler Effect

Shock Wave



60


What is a wave?

a periodic disturbance in a medium

What does it do?

Transfers energy

List some examples of waves:

Water, sound, light, seismic, electricity, wind, etc.


What is the source of all waves?

A vibration

Periodic Motion

-

(Pendulum)



a vibration that occurs at regular intervals
of time. One period is the time to make one complete vibration


Demo: super slinky

How do we represent waves?


A curvy line

Demo: marker on white board


-

mathematically this is called a:

sine curve


Wave pulse



a single disturbance in a medium


Phase

-

(conceptually represented)


the direction of the wave pulse


Phase up



a pulse above the neutral line


Phase down



a pulse below the neutral line


Mechanical waves

-

(2 types)



waves that exist in a matter medium. Ex.
water, sound, seismic




matter doesn’t move with the wave
-

only the energy is transferred!




61

Transverse



wave disturbance is perpendicular to the wave speed.


ex. water surface waves



visual representation:


Longitudinal



wave disturbance is parallel to the wave speed.


Ex.
sound



visual representation:


Electromagnetic waves



waves created by alternating electric fields,


Ex. light

What do waves transmit?


energy

How fast do waves travel?

it depends on the type of wave and the med
ium

Each kind of wave possesses the following
:

amplitude, crest, trough, neutral line, wavelength



Crest






Amp.










Neutral Line






Trough




Wavelength


Representing longitudinal waves
: (Sound)




Compressions



the crest for a longitudinal

wave, it is the area of higher
pressure.


62

Rarefactions

-

(Expansions)



the trough of a longitudinal wave, it is the
area of lower pressure.


Amplitude



the distance between the
neutral line and the peak of the phase

it is related to how much energy the wave carries.


Wavelength

-

(symbol =

)


the distance covered by a wave in one period, the
distance of one full crest and trough



Period

-

(symbol = T)
the time for one complete vibration or wave.



Frequency

-

(symbol = f)


how many waves or vibrations occur per unit time



Looking at the units, what do you think the relationship is between period
and frequency?
f = 1/T

Wavespeed

-

(symbol = v)


how fast a wave travels through a medium. It is
the distance

covered per unit time through the medium.



You’re at a Railroad crossing and notice that
2 train cars pass by
the lights in 1 sec. Each train car is 18 m long. How fast is the train
going?


V =
2 train cars/ sec. x 18 m / train car = 36 m/s


Do a unit analysis to find out what the relationship between wavespeed,
period, frequency, and waveleng
th.



Wavespeed equation
:


v =

f




63


What determines th
e speed of the wave?


the properties of the medium.


What happens when the frequency of the vibration is increased?

the wavelength decreases

What happens when the wavelength is increased?

The frequency decreases


1.

Calculate the wavelength of your favorite tone from the signal
generator: The speed of sound in air

is 343 m/s.




2.

Calculate the period of vibration for the speaker producing your
favorite tone from above:




3.

Calculate the wavelength of your favorite FM and AM radio station: The
speed of light is 3 x 10
8

m/s.



1.

What is the period of a 100 Hz wave?

T = 1/100 = 0.01 s


2.

A skyscraper sways back and forth with a period of about 4 s.

What is the frequency of vibration?

f = ¼ = 0.25 Hz


Assignment Ch. 25:
1
-
11,
26, 27, 31, 32, 35, 37




64


What are tidal waves and tsunamis?

Large waves that occur in the ocean due to the moon or earthquakes.

What are
Rogue waves (Freak waves) and why are they different than the other
waves?

Large waves that will suddenly appear at random.

How are these Rogue waves created?

Due to constructive wave interference.

Demo: superslinky

Interference


(2 kinds)


two or more
waves that meet in a medium, they will
algebraically add together to form a new wave.



Constructive



waves meet in phase and create a larger wave.




+

=




Destructive



waves meet out of phase and create a smaller wave.





Partial:





+





=





C
omplete:

+

=


Ex. noise canceling headphones, military helicopters,

laser beams

Watch video series: Freak Waves




65


What happens when the incident wave from a source interferes with its own
reflected wave?

A standing wave is
formed

Demo:superslinky
,
standing wave animation

Standing wave



a stationary wave form created by interference from its own
reflected wave



Anti
-
Node



area of max. displacement due to constructive interference




Node



area of min. or no displacement due to destructive interference


Video
: Tacoma Narrows Bridge

What is the relationship between the number of AN’s and the frequency of the
wave produced?
Direct. Increase the freq. you increase the # of AN’s


What happens to the wavelength of the slinky when the frequency is increased?

Wavelength goes down.

What’s happening to the size of the AN’s?

AN size decreases

1/2


standingwave
:





standingwave
:


11/2


standingwave
:









Is it possible for one wave to cancel out another wave so that the
combined wave amplitude is zero?

Yes. Application: noise canceling headphones

2.

Suppose you set up a standing wave with only 1 AN. If you shake the
slinky with twice the frequency, how many AN’s will appear? If you
shook it 3 times as fast?

2, 3

Assignment Ch. 25:
12
-
14, 22


66


What happens to sound if the source or observer is moving?

The pitch appear
s to change.

Demo: Mr. Doppler,
Videos

Doppler Effect



the apparent shift in frequency due to the relative motion
of the source and observer


toward



higher pitch



away



low pitch




works for all types of waves!
-

transverse, longitudinal, and
electromagnetic



wave speed






1




2




Boats on water, radar/Laser guns



Boat 1 travels against the velocity of the wave crests. Boat 1 wil
l
encounter _
more
_ wave crests per unit time.




Boat 2 travels with the velocity of the wave crests. Boat 2 will
encounter __
less
__ wave crests per unit time.

Each boat will perceive a different frequency than the frequency measured by
a stationary observer
.

What happens when the boat or any other source travels faster than the wave
speed of the material?
Wave crests will bunch up and overlap constructively

Bow Waves



“v” shaped wave form created by boats traveling faster than the
wavespeed of surface waves

Shock Waves


cone shaped high pressure area created by an object traveling
faster than the speed of sound



Sonic Boom



loud thunder clap created by the high pressure of a shock
wave

Video clips: aircraft breaking the sound barrier

Assignment Ch.
25
:
15
-
21, 45
-
49


67




Write down key terms with their definitions for each chapter.




Write down the equations used in eac
h chapter.




Solve the following example questions:

1.

How is a sine curve related to a wave?


2.

Draw a sine curve and label the following: Amplitude, crest, trough,
wavelength, neutral line




3.

Does the medium travel with the wave? Explain.



4.

As the frequency of

sound increases what happens to the wavelength?


5.

Describe the two different kinds of interference and what creates them.



6.

What causes a standing wave?



7.

Draw a 1 wavelength standing wave and label the following parts: anti
-
node, node.



8.

The Sears tower i
n Chicago sways back and forth with a period of 8
seconds. What is the frequency of vibration?



9.

Calculate the speed of a wave if the crests are 0.3 m apart and two
crests pass by a stationary point in 2 seconds.



68

10.

Calculate the wavelength of a 200 Hz sound

in air, assume the
speed of sound is 340 m/s.



11.

How far, in terms of wavelength, does a wave travel in one period?


12.

What do the concentric circles on the surface of a pond indicate
about the wave speed?


13.

Does the Doppler effect

occur for some types of waves or all types
of waves?


14.

What effect does the speed of a moving source have on the wave
speed of a sound wave?


15.


The frequency of a favorite radio station is 103.1 MHz. What
would be the wavelength of this radio signal? The sp
eed of light is 3 x
10
8

m/s.
( M = 1,000,000)





69






Chapter
26

Highlights:





Properties of Sound





Loudness





Making Sound Louder





Sound Interference














Key Terms









Sound

Crest

Trough

Pitch

Infrasonic

Ultrasonic

Amplitude

Decibels

Resonance

Forced Vibration