PHYSICS 101 (Physics for the Nonscientist)

Dr. Anatoli Frishmanfrishman@iastate.edu

Web Page: http://course.physastro.iastate.edu/phys101/

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Introduction

•What is physics?•A science•A basic science•The most basic science•Discovered by several generations of scientists

•Physics and measurements•Relationships between experiments and theory•Mathematics - language of science

Course organization•Lectures•Homework•Exams (multiple choice)

•two midterm exams and a comprehensive final exam•Formula sheet•Syllabus

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Physical quantities, units and standards

What do we measure? - Physical quantities.Units - a unit is a measure of the quantity that is defined to be exactly 1.

Examples: meter, mile, gram, kilogram.Standard - a reference to which all the other examples of the quantity are compared.Base quantities, and their standards.

The International System of Units (metric system)

Quantity Unit name Unit symbol Standard

Length Meter m Distance traveled by light in 1/299,792,458 second

Time Second s Time required for 9,192,631,770 periods of radiation emitted by cesium atoms

Mass Kilogram kg Platinum-iridium cylinder in International Bureau of Weights and Measures at Sevres, near Paris

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Other systems of units

•CGSE System of Units (metric system):

centimeter, gram, second

1m = 100cm

1kg = 1000g

•British engineering system

This system has force instead of mass as one of its basic quantities, which are feet, pounds, and seconds.

1 m = 3.281 ft; 1 inch = 2.54 cm1 kg = 0.06585 slug (Not the same as weight!)

on Earth 1 kg weighs 2.205 lb, on the Moon 1 kg weighs 0.368 lb

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Multiples of Units10-24 yocto- y

10-21 zepto- z

10-18 atto- a

10-15 femto- f

10-12 pico- p

10-9 nano- n

10-6 micro-

10-3 milli- m

10-2 centi- c

103 kilo- k

106 mega- M

109 giga- G

1012 tera- T

1015 peta- P

1018 exa- E

1021 zetta- Z

1024 yotta- Y

Conversion of units:

Multiply by the appropriate representation of 1 to cancel the unwanted units away

Converting between metric units is easy, as it only involves powers of 10.

Example 1: Convert 3kg into gram

mile

m

s

h

h

mile

h

mile

1

1609

3600

11010

m/s.474

Example 2: Convert 10 mph into m/s

gkg

gkgkg 3000

1

100033

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Significant figures

When we measure something, there’s a limited accuracy: result error (or accuracy)

Example 1: 2.35 0.01

Example 2: Wrong: 2.35 0.1 Correct: 2.4 0.1

Example 1: 0.24630

1sf 0.22sf 0.253sf 0.2464sf 0.24635sf 0.24630

Example 2: Not so clear in some cases: 200 (1,2,3 ?)

Scientific notation is crystal clear: 2 102 (or 0.2 103) 1sf2.0 102 (or 0.20 103) 2sf2.00 102 (or 0.200 103)3sf

Measurements and uncertainty

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Physics

Mechanics Thermal properties Electromagnetism Optics Atoms & particles

•Electrostatic•Electric current•Magnetism

•Geometrical optics•Wave optics

Condensed Mater High energy Biophysics

Classical physics Quantum physics

Relativistic physics Quantum relativistic physics

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MECHANICS

KINEMATICSKinematics is the study of motion, without the investigation of the cause of the motion

1. Motion

•Motion of what? Material point (An object with an irrelevant dimension for the purposes of a particular problem)•Development of models

Example: linear motion versus rotational•Motion is relative to the object of reference

Examples: the motion of an airplane passenger relative to the airplane, or the motion of an airplane passenger relative to the ground.

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sttt initialfinal 2

t

dv

2. One dimensional (1D) uniform motion(Motion along a straight line with a constant speed)

Example:

mssmtvd 102/5

sms

mv /5

2

10

mddd initialfinal 10

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Speed:

Distance:

tvd

ddd ttt

dt

finalfinal

initialinitial

and then

,0 and 0 If

Time interval:

Note: In science, the capital Greek letter Δ means difference.

3. Speed

initialfinal

initialfinal

tt

dd

t

dv

Definition:(total distance over total time)

10

t

dv

t

0

lim

a) Average speed:

b) Instantaneous speed:

Definition:

Question: If the average speed is non-zero over some time interval, does this mean that the instantaneous speed is never zero during the same interval?

A) Yes B) No C) It depends

A B

Example 1

Given:1d

Formula used:

t

dv

Solution:

?v

km/hv

km/hv

kmx

dd

kmdAB

60

40

502

100

2

1

21

4812/25

100

12

25

6

5

4

5

6

5

60

50 ;

4

5

40

50

21

2

22

1

11

km/h h

km

t

dv

h hh ttt

h km/h

km

v

dth

km/h

km

v

dt

2d

Answer:

/h48kmv 11

Example 2

Given:

?

60

40

1

2

1

21

v

km/hv

km/hv

httFormula used:

t

dv

Solution:

km/hh

km

t

dv

ht

kmkmkmddd

kmdd

502

100

2

1006040

60 km40

21

21

Answer:

km/hv 50

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