1. PHYSICS 231 INTRODUCTORY PHYSICS I
Lecture 1

2. PHYSICS 231 INTRODUCTORY PHYSICS I
Lecturer: Carl Schmidt (Sec. 001)
(517) , ext. 2128
Office Hours:
Friday 1-2:30 pm in 1248 BPS
or by appointment

3. Course Information

4. Succeeding in Physics 231 Do your homework (yourself) !
Use the help room (1248 BPS) !
Make sure you understand both “why” and “why not”
Interrupt the lecturer!

5. General Physics First Semester (Phy 231) Mechanics Thermodynamics
Simple harmonic motion
Waves
Second Semester (Phy 232)
Electromagnetism
Relativity
Modern Physics
(Quantum Mechanics, …, etc.)

6. Mechanics Chapter 1: the Basics
Used by all of physics and other sciences
Foundations laid by Galileo and Newton
Newton’s Principia
Chapter 1: the Basics
SI Units
Unit conversions
Dimensional Analysis
Significant Figures

7. UNITS (Systéme Internationale)
Dimension
SI (mks) Unit
Definition
Length
meters (m)
Distance traveled by light in 1/(299,792,458) s
Mass
kilogram (kg)
Mass of a specific platinum-iridium allow cylinder kept by Intl. Bureau of Weights and Measures at Sèvres, France
Time
seconds (s)
9,192,631,700 oscillations of cesium atom

8. Standard Kilogram at Sèvres

9. Unit conversion Example 1.1
A car goes 50 miles/hour. What is that in m/s?
22 m/s

10. Dimensional Analysis
Dimensions (like units) can be treated algebraically.
Variable from Eq. x m t
v=(xf-xi)/t
a=(vf-vi)/t
Dimension L M T
L/T
L/T2

11. Dimensional Analysis Checking equations with dimensional analysis:
(L/T2)T2=L L
(L/T)T=L
Each term must have same dimension
Two variables can not be added if dimensions are different
Multiplying variables is always fine
Numbers (e.g. 1/2 or p) are dimensionless

12. No ! Yes, It “could” be. Example 1.2
Could the following equations be correct?
No !
Yes,
It “could” be.

13. Units vs. Dimensions Dimensions: L, T, M, L/T …
Units: m, mm, cm, kg, g, mg, s, hr, years …
When equation is all algebra: check dimensions
When numbers are inserted: check units
Units and dimensions obey same rules: Never add terms with different units
Angles are dimensionless but have units (degrees or radians)
In physics sin(Y) or cos(Y) never occur unless Y is dimensionless

14. Scientific Notation Useful for very large…
Distance to sun = m
= 1.5 x 1011 m
or small numbers:
radius of iron nucleus = m
= 4.4 x m

15. Prefixes
In addition to mks units, standard prefixes can be used, e.g., km, cm, mm, mm

16. Significant Figures
I measure the table length with my ruler. Which statement is more correct?
The length is 56.0 in. (or 5.60x101 in)
The length is in. (or 5.600x101 in)
Statement A.
General Rule:
Number of digits used in decimal or scientific notation (including trailing zeros, but not leading zeros) specifies significant figures (i.e, precision) of measurement.

17. Significant Figures Other rules:
When multiplying or dividing, keep the minimum significant figures of any factors:
(5.585)(7.4) = 41. =
When adding or subtracting, keep the least accurate decimal place of any of the numbers: =
= 115.7

18. Chapter 2: One-Dimensional Motion
Motion at fixed velocity
Definition of average velocity
Motion with fixed acceleration
Graphical representations

19. Displacement vs. position
Position: x (relative to origin)
Displacement: Dx = xf-xi

20. Example: Distance vs. Displacement
Distance between Des Moines, Iowa, and Iowa City, is listed as miles or km
Straight line, to very good approximation
Question:
If we take a round trip Des Moines – Iowa City – Des Moines,
what is the total distance and displacement for this trip?
Distance=365.2 km
Displacement=0

21. Average velocity Average velocity Can be positive or negative
Depends only on initial/final positions
e.g., if you return to original position, average velocity is zero

22. Example 2.1 Carol starts at a position x(t=0) = 1.5 m.
At t=2.0 s, Carol’s position is x(t=2 s)=4.5 m
At t=4.0 s, Carol’s position is x(t=4 s)=-2.5 m
What is Carol’s average velocity between t=0 and t=2 s?
What is Carol’s average velocity between t=2 and t=4 s?
What is Carol’s average velocity between t=0 and t=4 s?
a) 1.5 m/s
b) -3.5 m/s
c) -1.0 m/s

23. Graphical Representation of Average Velocity
Between A and D , v is slope of blue line

25. Instantaneous velocity
Let time interval approach zero
Defined for every instance in time
Equals average velocity if v = constant
SPEED is absolute value of velocity

26. Graphical Representation of Average Velocity
Between A and D , v is slope of blue line

27. Graphical Representation of Instantaneous Velocityx t
= Slope of tangent at that point

28. Graphical Representation of Instantaneous Velocity
v(t=3.0) is slope of tangent (green line)

29. Example 2.2a The instantaneous velocity is zero at ___ A) a B) b & d
C) c & e

30. Example 2.2b The instantaneous velocity is negative at _____ A) a B) b
C) c
D) d
E) e

31. Example 2.2c The average velocity is zero in the interval _____
A) a-c B) b-d C) c-d D) c-e
E) d-e

32. Example 2.2d A) a-b B) a-c C) c-e D) d-e
The average velocity is negative in the interval(s) _________

33. SPEED Speed is |v| and is always positive
Average speed is sum over |x| elements divided by elapsed time

34. Example 2.3 x (m) a) What is the average velocity between B and E? D4 6 8 10 12 A B C D E
a) What is the average velocity between B and E?
b) What is the average speed between B and E?
t (s)
a) 0.2 m/s
b) 1.2 m/s