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Pretest
1. What is relative motion?
2. What is the difference between distance and displacement?
3. How is average speed calculated?
4. On a distance-time graph, what does the slope represent?
Chapter 12
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Pretest (continued)
5. What is velocity?
6. How is acceleration related to velocity?
7. A backpack falls out of an open window. The backpack starts from rest and hits the ground 1.0 second later with a velocity of 9.8 m/s. What is the average acceleration of the backpack?
a. 9.8 m/s b. 9.8 mc. 9.8 m/s2 d. all of the above
8. How are mass and weight different?
Chapter 12
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Interest Grabber
Objects in Free Fall What factors affect a falling object? Perform the following simple activity to begin learning about the forces that act on falling objects.
1. Stand beside your desk. Hold a sheet of notebook paper level at eye level. Release the sheet of paper and watch it fall. Describe the motion of the paper.
2. Hold a sheet of notebook paper that has been crumpled into a tight ball at eye level. Release the crumpled paper and watch it fall. Describe the motion of the paper.
3. How do the motions of the flat sheet of paper and the crumbled ball of paper compare? What forces do you think are acting on each sheet of paper?
Section 12.1
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Combining Forces Acting on an Object
Figure 4
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Combining Forces Acting on an Object
Figure 4
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Combining Forces Acting on an Object
Figure 4
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Combining Forces Acting on an Object
Figure 4
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Combining Forces Acting on an Object
Figure 4
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Combining Forces Acting on an Object
Figure 4
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Reading Strategy
Building Vocabulary
Section 12.2
a. Inertia is the tendency of an object to resist a change in its motion
b. Mass
c. Mass is the amount of matter an object contains as measured by its inertia.
d. Weight
e. Weight is the force of gravity acting on an object.
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Newton’s Second Law Section 12.2
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Newton’s Second Law Section 12.2
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Newton’s Second Law Section 12.2
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Newton’s Second Law Section 12.2
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Effects of a Force on Acceleration
Figure 13
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Effects of a Force on Acceleration
Figure 13
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Effects of a Force on Acceleration
Figure 13
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Effects of a Force on Acceleration
Figure 13
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Effects of a Force on Acceleration
Figure 13
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Effects of a Force on Acceleration
Figure 13
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Reading Strategy
a. kg•m/s
b. mass (or velocity) c. velocity (or mass)
Section 12.3
Summarizing
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Conservation of Momentum
Figure 17A and 17B
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Conservation of Momentum
Figure 17A and 17B
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Conservation of Momentum
Figure 17A and 17B
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Conservation of Momentum
Figure 17A and 17B
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Conservation of Momentum
Figure 17C
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Conservation of Momentum
Figure 17C
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Reading Strategy
Comparing and Contrasting
Section 12.4
a. Neutrons and proton
b. Very short (decreases rapidly beyond the diameter of a few protons)
c. Very strong (100 times stronger than electrical repulsion force)
d. All particles
e. Short
f. Weaker than the strong force
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Gravitational Forces Acting on Masses at Different Distances
Figure 21
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Gravitational Forces Acting on Masses at Different Distances
Figure 21
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Gravitational Forces Acting on Masses at Different Distances
Figure 21
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Gravitational Forces Acting on Masses at Different Distances
Figure 21
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Forces Acting on the Moon
Figure 22
Pretest Answers
1. What is relative motion?
2. What is the difference between distance and displacement?
3. How is average speed calculated?
4. On a distance-time graph, what does the slope represent?
Distance is the length of a path between two points. Displacement is the direction from the starting point and the length of a straight line from the starting point to the ending point.
Chapter 12
Click the mouse button to display the answers.
Relative motion is movement in relation to a frame of reference.
Total distance is divided by total time.
The slope represents the speed.
Chapter 12Pretest Answers (continued)
Click the mouse button to display the answers.
Velocity is speed with direction.
Mass is a measure of inertia; weight is the measure of the force of gravity acting on an object.
5. What is velocity?
6. How is acceleration related to velocity?
7. A backpack falls out of an open window. The backpack starts from rest and hits the ground 1.0 second later with a velocity of 9.8 m/s. What is the average acceleration of the backpack?
a. 9.8 m/s b. 9.8 mc. 9.8 m/s2 d. all of the above
8. How are mass and weight different?
Acceleration is change in velocity, that is, any change in speed, direction, or both.
Interest GrabberAnswers
1. Stand beside your desk. Hold a sheet of notebook paper level at eye level. Release the sheet of paper and watch it fall. Describe the motion of the paper.
The paper flutters slowly to the ground.
2. Hold a sheet of notebook paper that has been crumpled into a tight ball at eye level. Release the crumpled paper and watch it fall. Describe the motion of the paper.
The crumpled sheet of paper falls straight to the ground.
3. How do the motions of the flat sheet of paper and the crumbled ball of paper compare? What forces do you think are acting on each sheet of paper?
The flat sheet of paper fluttered slowly to the ground whereas the crumpled ball of paper fell more quickly to the ground and followed a straight-line path. Do not assess students on correctly identifying the two opposing forces on the paper; accept any reasonable response. The two opposing forces are gravity and air resistance.
Section 12.1
Interest GrabberAnswers
1. Describe the behavior of two bar magnets that are positioned so that their north and south poles are nearly touching.
The opposite poles of the bar magnets attract each other. If the magnets are close enough, they will move together.
2. Describe a common behavior of clothes when they are removed from a clothes dryer.
Clothes removed from a clothes dryer often stick together.
3. How are these two forces the same? How are they different?
Both forces are associated with charged particles. Both forces attract. The magnets are pulled together by magnetic forces, whereas the clothes cling together because of electric forces.
Section 12.4
Chapter 12Go Online
Data sharing
Self-grading assessment
For links on forces, go to www.SciLinks.org and enter the Web Code as follows: ccn-2121.
For links on mass, go to www.SciLinks.org and enter the Web Code as follows: ccn-2122.
For links on Newton’s laws, go to www.SciLinks.org and enter the Web Code as follows: ccn-2123.
For links on gravity, go to www.SciLinks.org and enter the Web Code as follows: ccn-2124.
