# Motion Worksheet Physics

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```					               Chapter 3
Linear Motion
(Motion in a straight line,
such as falling straight downward)

13-Apr-11            Physics 1 (Garcia) SJSU
Demo: Cracking Nuts
What’s the best way to crack open
a nut?

13-Apr-11         Physics 1 (Garcia) SJSU
Tools you’ll learn today
• Speed and Velocity
• Acceleration
• Relationships among distance,
velocity, and acceleration.
• Falling motion.

13-Apr-11           Physics 1 (Garcia) SJSU
Speed
Define speed of an object as
(Distance traveled)
(SPEED) =
(Time elapsed)

For example, 30 miles per hour means object travels
distance of 30 miles in an elapsed time of one hour. Write
as,
miles
30 miles per hour = 30
hour

13-Apr-11              Physics 1 (Garcia) SJSU
Speed and Distance
From definition of speed,
(Distance traveled) = (Speed) X (Time elapsed)

Example: If speed is 30 miles per hour and time elapsed is
2 hours then distance traveled is (30)X(2) = 60 miles.

Match units: This time elapsed is also 120 minutes but it’s
not correct to compute distance traveled as
(30)X(120) = 3600 miles {WRONG}.

13-Apr-11               Physics 1 (Garcia) SJSU
Check Yourself
What is the average speed of a cheetah that
sprints 100 meters in 4 seconds? How about if it
sprints 50 meters in 2 seconds?

A car has an average speed of 100 kilometers per
hour. How far does it travel in 60 minutes?

13-Apr-11          Physics 1 (Garcia) SJSU
Average versus Instantaneous
Sometimes consider average speed, other
times we speak of instantaneous speed.

For example, say it takes you one hour to drive the 30 miles
from home to campus.

Average speed is 30 miles per hour.

Instantaneous speed (given by your speedometer) varies
due to traffic, stop lights, morons driving in front of you,
etc.
13-Apr-11                 Physics 1 (Garcia) SJSU
Demo: Ball Races
Which ball wins the race, A or B?
A

Finish
B
Line

Which ball has the larger average speed?
Which has the larger instantaneous speed at each point.

13-Apr-11               Physics 1 (Garcia) SJSU
Check Yourself
A car has an average speed of 60 miles per
hour. Is it possible for the instantaneous
speed to always be less than 60 miles per
hour?

13-Apr-11        Physics 1 (Garcia) SJSU
Velocity
Velocity is speed and
direction of object’s                         25 m/s, upward
motion.

Examples:
30 miles per hour, Northward
25 meters per second,                       25 m/s,
Downward                   downward
300 miles per hour,
Coming towards you
Same speeds
Different velocities
13-Apr-11          Physics 1 (Garcia) SJSU
Check Yourself
The speedometer of a car moving east
reads 100 km/h. It passes another car
moving west at 100 km/h. Do they have
same speed? Velocity?

During a certain period of time, the
speedometer of a car reads a constant 60
km/h. Does this indicate a constant
speed? Constant velocity?
13-Apr-11       Physics 1 (Garcia) SJSU
Changes in Velocity
Velocity changes if speed or direction of motion change.

Velocity changes
in both these cases.
10 m/s,
downward

25 meters per second,
25 m/s,            45 degrees upward
downward                                             25 meters per second,
45 degrees downward

13-Apr-11                 Physics 1 (Garcia) SJSU
Acceleration
Define acceleration as,
(Change in Velocity)
(ACCELERATION) =
(Time interval)
Note: An object accelerates anytime its velocity changes.
Examples include:
Object speeds up.
Object slows down (speed decreases).
Object speed constant but direction changes (curved path)

Best example of acceleration is objects in free fall

13-Apr-11                  Physics 1 (Garcia) SJSU
Demo: String of Falling Balls
Falling objects accelerate
(speed increases).
Listen for the sound as
balls hit the ground.
Time between “clicks”
gets shorter & shorter
(falling faster & faster).

String does not pull; no tension while falling.

13-Apr-11                           Physics 1 (Garcia) SJSU
Velocity in Free Fall (Down)
Release    Zero meters per sec.
How fast do objects go               1 second
10 meters per sec.
when they fall?
2 seconds
Acceleration of gravity                          20 meters per sec.

is 10 meters per
second per second.
3 seconds
With each second of                              30 meters per sec.
fall, speed increases
by 10 meters/second
4 seconds
13-Apr-11        Physics 1 (Garcia) SJSU
40 meters per sec.
Velocity in Free Fall (Up & Down)
Zero meters per sec.
Moving upward, with                       10 meters per sec.

each second the
20 meters per sec.
speed decreases by
10 meters/second.
Going back down the
motion exactly                            30 meters per sec.

reverses itself.
See Fig. 3.8 (pg. 47)
13-Apr-11       Physics 1 (Garcia) SJSU     40 meters per sec.
Position in Free Fall
Release
5 meters
How far do objects go                 1 second    Higher than
this ceiling
when they fall?
2 seconds   20 meters
More complicated
because speed is
increasing.
45 meters
There’s a pattern &                   3 seconds      Higher than
King library

Galileo figured it out.
But it wasn’t easy.
4 seconds
13-Apr-11         Physics 1 (Garcia) SJSU              80 meters
Galileo’s Inclines
Galileo realized that
rolling down an
incline and falling
were very similar.
It was much easier
for him to study the
slower motion of an
incline.

13-Apr-11         Physics 1 (Garcia) SJSU
Demo: Galileo’s Clicking Ramps
Roll balls down notched, inclined
ramps and listen for the clicks.
8      16       24            32          40   48        56    64

Start

1 4   9      16        25                  36         49             64
4=2x2 9=3x3 16=4x4    25=5x5              36=6x6     49=7x7        64=8x8
13-Apr-11                          Physics 1 (Garcia) SJSU
Position in Free Fall (cont.)
Release
5 meters
Galileo realized that:                         1 second
5=5x 1x1

(Distance Fallen) =
½ (Acceleration)(Time)(Time) 2 seconds           20 meters
20=5x 2x2

Gravity acceleration is 10
meters per second per second
so at a time of 3 seconds,                                  45 meters
3 seconds
45=5x 3x3
(Distance Fallen) =
½ (10)(3)(3) = 45 meters

4 seconds
13-Apr-11                  Physics 1 (Garcia) SJSU            80 meters
80 =5x 4x4
Lab: Acceleration of Gravity
Record position of falling object
using spark timer and paper
tape.

13-Apr-11         Physics 1 (Garcia) SJSU
Demo: Dropping the Ball
How long does it take a ball to fall 3 meters?
Using the formula,
(Distance Fallen) = ½ (Acceleration)(Time)(Time)

Can check that it takes 0.77 seconds since
(3) = ½ (10)(0.77)(0.77)

Beauty of science:
Predict, then verify by dropping balls!

Note: Do similar measurement in first experiment in the Phys 1L lab.
13-Apr-11                      Physics 1 (Garcia) SJSU
Demo: Catch a Buck
Put thumb and index fingers
Can you react fast enough
to catch the money?

13-Apr-11              Physics 1 (Garcia) SJSU
Demo: Reaction Time
Distance (inches)   Time (sec.)                                     Release
1              0.07
2              0.10
3              0.12
4              0.14
5              0.16
6              0.17
7              0.19
8              0.20
10             0.23
12             0.25
14             0.27                                 Catch
16             0.29
18             0.30

13-Apr-11                         Physics 1 (Garcia) SJSU

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