Physical Science Notes
3-5-08
Acceleration: The rate at which velocity changes over time
Math Skills
1. Natalie accelerates her skateboard along a straight path from 0 m/s to 4.0
m/s in 2 seconds. Find her average acceleration
Solution:
(4.0 m/s – 0.0 m/s) / 2.5 sec = 1.6 m/s2 along her path
2. A turtle swimming in a straight line towards shore has a speed of 0.50
m/s. After 4.0 seconds, its speed is 0.80 m/s. What is the turtle’s
acceleration?
Solution:
(0.80 m/s – 0.50 m/s) / 4.0 sec = 0.075 m/s2 toward the shore.
A constant: A quantity whose value does not change
Key Points:
A train station is a frame of reference for a train.
A city is a frame of reference for an airplane.
Different speeds in our everyday life
Person walking- 1.4 m/sec
Wheelchair racer- 7.3 m/sec
Galloping horse- 19 m/sec
High speed train- 69 m/sec
Speeding race car- 96 m/sec
Cruising jet257 m/sec
Page 367 graph Figure 4
1. Which line has the greatest slope? The cruising jet
2. Which line has the least slope? The walking person
3. Which would the shape of zero represent? An object at rest.
4. Does each line graph represent an object traveling at a constant speed or
are the speeds changing? Constant speed- see the graph: the lines are
straight
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Physical Science Notes
3-5-08
Page 369 Practice problems
Problem #1
Find the velocity in meters per second of a swimmer who swims 110 m
toward the shore in 72 s.
Velocity = distance / time
110 m/ 72 sec = 1.5 m/sec toward shore
Problem #2
Find the velocity in meters per second of a baseball thrown 38 meters from
third base to first base in 1.7 seconds.
38 m/ 1.7 sec = 22 m/sec toward first base
Problem #3
Calculate the displacement in meters that a cyclist would travel in 5.00 hours
at an average velocity of 12.0 km/h to the southwest. Remember to include
direction.
Distance
= velocity * time
= 12.0 km/h * 5.00 h
= 60 km to the southwest
Additional Example:
Suppose that a lion moves due east at different speeds so that it travels 25
km in 4.0 hours. What is the lion’s average speed?
Velocity
= distance/ time
= 25 km/4.0 hours
=6.2 km/hour
Page 371 Three graphs
What is the average speed of each car?
Fast moving car?
100m/3.3 sec= 30 m/sec
Slow moving car?
50 m/5.0 sec = 10 m/sec
Car with changing speeds?
60 m/ 5.0 sec = 12 m/sec
Section 1 Review page 371
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Physical Science Notes
3-5-08
1. Explain the relationship between motion and frame of reference.
When an object changes position with respect to a frame of reference the
object is in motion.
2. Identify the following measurements as speed or velocity
a. 88 km/h
speed
b. 9 m/s to the west
velocity
c. 18 m/s down
velocity
d. 10 m/s
speed
3. Describe the measurements necessary to find the average speed of a
high school track athlete. Measure the distance the athlete travels and
the time required to travel that distance
4. Determine the unit of a caterpillar’s speed if you measure the
distance in centimeters (cm) and the time it takes to travel that
distance in minutes (min). How would you graph the data? cm/min;
time on the horizontal axis and distance on the vertical axis
5. Imagine that you could ride a baseball that is hit hard enough for a
home run. If the baseball is your frame of reference, what does the
Earth appear to do? The Earth appears to travel backwards for the
distance baseball travels and at the speed at which the baseball travels.
6. How much time does it take for a student running at an average
speed of 5.00 m/s to cover a distance of 2.00 km? 2 km = 2000 meters
2000 meters/ 5 m/sec = 4.00 x 102 sec or 6.67 minutes
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