Pre-Class Friday 1-13-12

1
Pre-Class Friday 1-13-12
Relative Velocity

• Garfield is walking at 1 m/s, but the wind is
  blowing him at -3 m/s. What velocity does Jon
  think he has?

2
Chapter 3 Accelerated Motion

• Uniform motion constant speed or velocity

• Nonuniform motion changing speed or velocity

3
Measuring velocity (in meters per second, m/s)

• Velocity interval is defined as
• ?v vf - vi
• The i is initial and the f is final

D (Greek letter delta) stands for change in
or final - initial
4
ACCELERATION

• Acceleration is the measure of the change in
  velocity over a given time
• Constant velocity means no acceleration

• Dv
• a
• Dt

a average acceleration (m/s2) v velocity
(m/s) t time (s)
5
Velocity-Time graph

• Similar to Position-Time graph
• Displays the velocity of an object at any time
• Slope of the line shows the average acceleration

6
Pre-Class for Tuesday 1-17-12

• All of the following can be found on a
  velocity-time graph except for

1. Average acceleration
2. Inertia
3. Velocity
4. Time

7
EQUATIONS OF MOTION

• vf vi a t
• x vi t 1/2 a t2
• vf2 - vi2 2 a x
• x (vf vi) t/2

8
Pre-class for Wednesday 1-18-12
Section
3.2

• A car is moving with an initial velocity of vi
  m/s. After reaching a highway, it moves with a
  constant acceleration of a m/s2, what will be the
  velocity of the car after traveling for t seconds?

1. vf vi at
2. vf vi 2at
3. vf2 vi2 2at
4. vf vi at

9
ACCELERATION BY GRAVITY

• The Earth constantly accelerates all objects
  towards its center
• We use the variable g for the acceleration of
  gravity
• g 9.8 m/s2
• a - g - 9.8 m/s2
• (different from book)

10
Taking a closer look
11
EQUATIONS OF MOTION

• vf vi - g t
• y vi t - 1/2 g t2
• vf2 - vi2 - 2 g y

12
CHAPTER 3

• 94. 60 m/s
• 95. 50 m yes, 21.76 m/s
• 97. 1.2 s
• 98. -78 m/s, -310 m
• 99. -20 m/s, -20 m
• 100. -7.3 m/s
• 102. 5.9 m, 10.8 m/s
• 105. 8 m
• 107. 280 m/s2, 29g
• 109. 3.1x108 m/s2, 11ms
• 113. 1.56 m
• 115. -15 m/s,-10 m, 20 m

• 80. 8 m/s2
• 81. 33 m/s
• 82. 6 m/s2, 0 m/s2, -2 m/s2, -4 m/s2
• 85. Car B,Car AC tie
• 86. 607 m/s, 1.83 mach
• 89. 43.2 m, 43.2 m
• 138m, 550m
• 92. 924 m

13
Pre-class Thursday 1-19-12
Section
3.2

• What is the accepted value for the acceleration
  of gravity?

14
FALLING LAB

• Materials
• 6 pennies
• stop watch
• meter stick
• tape
• Objective
• determine the acceleration of gravity
• Each group will turn a paper into me today.

15
PROCEDURES

• Stack five pennies and tape them together.
• Drop the five pennies from 3 different heights.
• Measure the distance fallen and the time it took
  to fall to the ground.
• Determine the acceleration of gravity.
• Repeat the experiment for the single penny.
• Complete the chart on the next slide and answer
  the questions.

16
FILL OUT THE CHART

1. Find the percent difference between your answer
   and the accepted answer.
2. How could you improve your results (at least 2
   examples)?

Questions
17
EQUATIONS OF MOTION

• vf vi a t
• x vi t 1/2 a t2
• vf2 - vi2 2 a x

18
Pre-class Thursday 1-22-09

• Write
• Review 4 test

19
TEST OVER CHAPTER 3

• Take a few minutes to review/finish pre-class
  problems.
• You need your own paper.
• Do not write on my paper.
• Box in final answers.
• Write clearly.
• You may need a calculator.