Unit 1

Unit 1

Units and Measurements






© 2006, B.J.
Lieb

Giancoli
,
Sec. 1
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1


1
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8


What is Physics ?

Studies Fundamental Forces in Nature

Gravity

Electricity &
Magnetism

Strong

Nuclear


Weak

Nuclear

Studies Small and Large Systems

Unit 1
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02

Subfields of Physics ?

•
Includes
; acoustics, astrophysics, atomic physics, cryogenics,
electromagnetism, elementary particle physics, fluid dynamics,
geophysics, mathematical physics, mechanics, molecular physics,
nuclear physics, optics, plasma physics, quantum physics, solid
state physics, statistical mechanics, thermodynamics
.

Unit 1- 03
CAT Scan

Brain

X
-
Ray

Medical Applications

Sonogram

MRI

Topics Covered in PHYS 243

•

Classical Mechanics

•
Fluids

•
Vibrations and Waves

•
Sound

•
Thermodynamics

Unit 1
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04

Measurement Uncertainty

In lab you will have to
estimate the uncertainty in
any measurement. The
result might be

X

=8.8 cm
±

0.1cm


Another way to show
uncertainty is the number
of significant figures
–

the
number of reliably known
digits, which might be two
in this case.

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05

Significant Figures

•

0.0034 has two significant figures

•

44.58 has four

•

800 has one, 8.00x10
2

has three

•

Multiplication
or D
ivision:
the final
result should
have only as
many digits as the number with the least number of significant
figures used in the calculation.



23.66
x 1.1 =
26.03=26 (two)

•

Addition
or
Subtraction
:
the final
result is
no more accurate
than the least accurate number used.


23.5 + 43.2 + 44 = 110.7 = 111


Unit 1
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06

Significant Figures

in Mastering Physics

•
Mastering Physics (MP) is very strict and intolerant about significant.
Most problems expect three significant figures. Fortunately you can answer
every question 20 times.

•
MP
advises students to carry the full precision on intermediate results until
they obtain the final answer. They should apply their rounding rules only on
the final answer.

•
When the student's answer is within tolerance of the full
-
precision answer,
the score is not penalized, the number of wrong answers is not
incremented, and the feedback reads: "Very close. Check the rounding and
number of
significant

figures

in your final answer."

•
When the student's answer is further off, but still within a looser tolerance
of the full
-
precision answer, the score is penalized, the number of wrong
answers is incremented, and the feedback reads: "Not quite. Check through
your calculations; you may have made a rounding error or used the wrong
number of
significant

figures
."


Unit 1
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07

5. Units, Standards and SI System

Length: 1 meter

defined as the distance light travels in
1 / 299,792,458 of a second.

Mass: 1 kilogram
defined as a
standard mass

of a certain
cylinder kept near Paris

Unified Atomic Mass: 1 u
defined as the 1/12 of the mass of
the
12
C atom.

1u = 1.6605 x 10
-
27

kg

Time: 1 second
defined by a cesium clock.

Unit 1
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08

Metric Prefixes
You Must
Know

giga

G

10
9

mega

M

10
6

kilo

k

10
3

centi

c

10
-
2

milli

m

10
-
3

micro



10
-
6

nano

n

10
-
9

pico

p

10
-
12

femto

f

10
-
15

Unit 1
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9

Math Symbols You Must Know


x > y


x
is greater than
y


y < x


y
is less than
x


y << x


y

is much less than
x


y


x


y
is approximately equal
x


y


x


y
is defined equal to
x



x


change in
x

Unit 1
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10

Converting Units

•
You are strongly urged to use the standard way of doing
units conversion in physics. It reduces errors and is much
easier for the grader to check.

•
It is based on the fact that you can multiply anything by ‘1’
without changing its value.

Example:
1 inch = 2.54 cm Thus

Example:
The area of a surface 5.0 in by 3.0 in is

Unit 1
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11

Order Of Magnitude Estimate

•

It is a good idea to do a rough estimate before doing a
detailed calculation

•
Then when you work the problem, ask yourself if the
result appears reasonable.


Unit 1
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12

Dimensions and Dimensional Analysis

•

In order to be correct, an answer must have the correct
units.

•
Your solution must include units to show how they
work out

•
You can often use units to guide you to the answer.

•
Useful Rule: We can add or subtract quantities only if
they have the same dimensions.

•
Example:

Each term must have units of length.

Unit 1
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13

Math Review

•
I have created two review tutorial/quizzes in Mastering
Physics:

•
Algebra Review
–

needed for Unit 2 (Chapter 2)

•
Trigonometry Review
–

needed for Unit 5 (Chapter 3)

•
These count the same as a homework. The deadline is
extended but you need to know the material ASAP.

•
Appendix A has an excellent summary of the math you
need for this course. You must understand all of the
material in Appendix A
-
1, A
-
2, A
-
3, A
-
4 and A
-

7.


Unit 1
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Unit 1 Appendix

Unit
1
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Photo and Clip Art Credits


Some
figures electronically reproduced by permission of Pearson Education, Inc., Upper
Saddle River, New Jersey

Giancoli
, PHYSICS,6/E
© 2004.


Slide

1
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2 Photos and Clipart: Microsoft Clipart Collection, reproduced under general license for educational
purposes.

1
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3 Photo and Clipart:
Microsoft Clipart Collection, reproduced under general license for educational
purposes.