Go to section 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

Go to section 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/sb.9.8 m c.9.8 m/s 2 d.all of the above 8.How are mass and weight different? Chapter 12

Go to section 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

Go to section Reading Strategy Relating Text and Visuals Section 12.1 e.Yes f. No motion g. Yes h. No motion a.Yes b. No motion c. Yes d. No motion i.No j. Potted plant accelerates.

Go to section Combining Forces Acting on an Object Figure 4

Go to section Combining Forces Acting on an Object Figure 4

Go to section Combining Forces Acting on an Object Figure 4

Go to section Combining Forces Acting on an Object Figure 4

Go to section Combining Forces Acting on an Object Figure 4

Go to section Combining Forces Acting on an Object Figure 4

Go to section Interest Grabber Describing Motion Imagine you are carrying a bowl of soup on a food tray as you walk toward your favorite table. Suddenly, someone walks in front of you. You stop abruptly to avoid a collision. 1.Describe the motion of the soup in the bowl immediately after your abrupt stop. 2.Explain why you think the soup in the bowl behaved the way it did. Section 12.2

Go to section 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.

Go to section Newton’s Second Law Section 12.2

Go to section Newton’s Second Law Section 12.2

Go to section Newton’s Second Law Section 12.2

Go to section Newton’s Second Law Section 12.2

Go to section Effects of a Force on Acceleration Figure 13

Go to section Effects of a Force on Acceleration Figure 13

Go to section Effects of a Force on Acceleration Figure 13

Go to section Effects of a Force on Acceleration Figure 13

Go to section Effects of a Force on Acceleration Figure 13

Go to section Effects of a Force on Acceleration Figure 13

Go to section Interest Grabber Changing Motion Did you know that billiard balls can be used to study the transfer of energy between objects? 1.Describe the motion of the balls in Figure A. 2.Figure B shows the motion of the billiard balls after impact. Explain why the motion of the balls changes in Figure B. Section 12.3

Go to section Reading Strategy a.kgm/s b.mass (or velocity) c.velocity (or mass) Section 12.3 Summarizing

Go to section Conservation of Momentum Figure 17A and 17B

Go to section Conservation of Momentum Figure 17A and 17B

Go to section Conservation of Momentum Figure 17A and 17B

Go to section Conservation of Momentum Figure 17A and 17B

Go to section Conservation of Momentum Figure 17C

Go to section Conservation of Momentum Figure 17C

Go to section Interest Grabber Comparing Forces No matter where you are in the universe, certain types of forces are present. You are already familiar with two of these forces—electric force and magnetic force. 1.Describe the behavior of two bar magnets that are positioned so that their north and south poles are nearly touching. 2.Describe a common behavior of clothes when they are removed from a clothes dryer. 3.How are these two forces the same? How are they different? Section 12.4

Go to section 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

Go to section Gravitational Forces Acting on Masses at Different Distances Figure 21

Go to section Gravitational Forces Acting on Masses at Different Distances Figure 21

Go to section Gravitational Forces Acting on Masses at Different Distances Figure 21

Go to section Gravitational Forces Acting on Masses at Different Distances Figure 21

Go to section 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 12 Pretest 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/sb.9.8 m c.9.8 m/s 2 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 Grabber Answers 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 Grabber Answers 1.Describe the motion of the soup in the bowl immediately after your abrupt stop. The soup in the bowl continues forward and spills over the bowl’s front edge onto the food tray. 2.Explain why you think the soup in the bowl behaved the way it did. The soup’s motion is explained by momentum. The momentum of the soup keeps it moving forward after the forward motion of the food tray has been halted. Section 12.2

Interest Grabber Answers 1.Describe the motion of the balls in Figure A. The racked balls in Figure A are motionless. The cue ball moves in a straight line and at high speed toward the racked balls. 2.Figure B shows the motion of the billiard balls after impact. Explain why the motion of the balls changes in Figure B. The high-speed cue ball strikes the motionless balls and transfers momentum and kinetic energy to them, causing them to move. Section 12.3

Interest Grabber Answers 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 12 Go Online Data sharing Self-grading assessment For links on forces, go to and enter the Web Code as follows: ccn For links on mass, go to and enter the Web Code as follows: ccn For links on Newton’s laws, go to and enter the Web Code as follows: ccn For links on gravity, go to and enter the Web Code as follows: ccn

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