Fundamentals of motion

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14 Νοε 2013 (πριν από 4 χρόνια και 8 μήνες)

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Fundamentals of motion

Kinematics

Is the study of motion

The how, not the why

An object’s
position

means…

The location of object in space

How do we know if something
moves?

FRAME OF REFERENCE

RELATIVE MOTION

Frame of reference

An object or place used for comparison to
the main subject.

Reference Point

You get to pick what your measuring the
position of the object against

You get to pick positive and negative
direction

What is the most common reference
point?

Earth, ground or something attached to it

Reference

Reference point or
Frame of Reference

-
what is used to
determine motion of
an object

Standard frame of
reference is the solid
Earth

Relative motion

How fast is that car
moving on the highway?

If moving in the opposite
direction,

the
velocities of each object

If moving in same
direction,
subtract

the
velocities of each

SCALAR VS VECTOR VALUES

Comparison

Vector Values

Any vector value must
indicate:

a magnitude

a direction for the value

a unit of measure

Magnitude means the size

Ex:
-
12.3 m/s

(
-
) indicate direction

12.3 indicates size

m/s are the units

Scalar Values

Only indicate magnitude
and units

VALUES OF MOTION

What values are measured
about the motion of an object?

Can you think of 3?

Values of Motion

How Far?

How Fast?

Is the motion unchanging?

DISTANCE AND
DISPLACEMENT

The measurement of how far

Measures the length that someone moves

Measured in meters (m)

Two ways that this can be accomplished

Use the same symbol for representation of
length measurement: d

Displacement and Distance

Displacement

Length of straight line
between initial and
final position

Direction matters

Distance

Length of the path
followed between
start and final position

Direction does not
matter

Distance

Measures the length
of the path taken by
an object from one
point to the next

Standard unit of
measure is meters

Displacement

Measurement of the
straight line length
between start position
and final position

Standard units are
measured in meters

Direction does matter

Similarities

Both measure length and use same units

Can you think of an example
when an object’s distance
value is the same as its
displacement?

Your car has to travel a displacement
of 5 meters (twice)

That means the length between your start
position and final position has to be
greater than 5 meters

To determine displacement, use a tape
measure, count blocks on the hallway floor
or use string

Identifying start and final position for

Start position:

Point where left front wheel touches the
ground

Final Position:

Point where left front wheel touches the
ground

SCALAR AND VECTOR
VALUES

Types of measurement

Velocity

Displacement/time

Direction matters

Units are m/s

Speed

Distance/time

Direction is not
indicated

Units are m/s

SPEED AND VELOCITY

Measure the rate of motion

How fast an object travels

Determined by how far it travels over an
amount of time

Rate (fraction)

Speed, velocity

Speed is distance / time

Velocity is displacement / time

Velocity will indicate a direction

Both measure rate of motion (how fast)
and use same units

Speed

A rate of motion
which

How much distance
traveled in an amount
of time

Standard units are
m/s

Velocity

Also a rate of motion

Change of position (displacement) over
time

Same units

Direction does matter

Difference between velocity and
speed

Speed is calculated using distance

Velocity uses displacement

Therefore the velocity value should
indicate a direction

Average speed, velocity

Are rates of motion calculated over a time
period

Velocity = overall displacement / time

Speed = overall distance / time

Average Speed

Speed found by taking the overall distance
divided by the overall time

Rate of motion over a period of time

Not at any single point in time

Measurement of speed

Average velocity = displacement / time

Average speed = distance / time

Symbol in the book will be same = v

Equation

v = d / t

Constant speed

Rate of motion does not change over a
period of time

Cruise control

Desktop computers

Constant speed, velocity

Occurs when the rate of motion does
NOT

change

Instantaneous speed

Rate of motion at a single point in time

Harder to calculate than average speed

Difference between average and
instantaneous speed

Average
: measured over some amount of
time

Instantaneous
: at one moment of time

Instantaneous Velocity

-
vs
-

Average velocity

Instantaneous means at one infinitesimally
small point in time

Find by measuring the slope of the tangent line

Average means over a measurable block
of time

Find by calculation

Resultant velocity

Finding the overall velocity of an object given a
specific frame of reference by combining rates of
motion

Person on bus compared to earth

Person in airplane compared to earth

Average, Instantaneous,
Constant, Resultant are words
that can be used describe
speed
or velocity

Meanings are the same

How to calculate average velocity

V = d

t