Motion Preview Understanding Concepts Reading Skills Interpreting Graphics

Understanding Concepts A meteorologist describes a tropical storm as traveling northwest at 50 mi/h. Which attribute of the storm’s motion has the meteorologist described? A. force B. acceleration C. velocity D. displacement

Understanding Concepts A meteorologist describes a tropical storm as traveling northwest at 50 mi/h. Which attribute of the storm’s motion has the meteorologist described? A. force B. acceleration C. velocity D. displacement

Understanding Concepts, continued 2. Which of the following must be applied to move an object at rest, such as a large rock? F. static friction G. kinetic friction H. balanced forces I. unbalanced forces

Understanding Concepts, continued 2. Which of the following must be applied to move an object at rest, such as a large rock? F. static friction G. kinetic friction H. balanced forces I. unbalanced forces

Understanding Concepts, continued 3. A fish swimming at a constant speed of 0.5 m/s suddenly notices a shark appear behind it. Five seconds later, the fish is swimming in the same direction at a speed of 2.5 m/s. What was the fish’s average acceleration? A. 0.4 m/s2 B. 0.6 m/s2 C. 1.7 m/s2 D. 2.5 m/s2

Understanding Concepts, continued 3. A fish swimming at a constant speed of 0.5 m/s suddenly notices a shark appear behind it. Five seconds later, the fish is swimming in the same direction at a speed of 2.5 m/s. What was the fish’s average acceleration? A. 0.4 m/s2 B. 0.6 m/s2 C. 1.7 m/s2 D. 2.5 m/s2

Understanding Concepts, continued 4. Bowling lanes are made as smooth as possible in order to minimize kinetic friction. Why is this desirable in a bowling lane?

Understanding Concepts, continued 4. Bowling lanes are made as smooth as possible in order to minimize kinetic friction. Why is this desirable in a bowling lane? Answer: The less kinetic friction that is exerted on a bowling ball, the more speed a bowling ball will be able to maintain as it rolls down a lane. The faster the ball is going, the more pins it is likely to knock down.

Understanding Concepts, continued 5. Two amateur entomologists are observing the movement of a beetle traveling in a straight line across a driveway. Every 10 s, they measure the distance that the beetle has traveled. Afterward, they create a graph of the beetle’s motion, with distance on the y-axis and time on the x-axis. What does the slope of their graph represent?

Understanding Concepts, continued 5. Two amateur entomologists are observing the movement of a beetle traveling in a straight line across a driveway. Every 10 s, they measure the distance that the beetle has traveled. Afterward, they create a graph of the beetle’s motion, with distance on the y-axis and time on the x-axis. What does the slope of their graph represent? Answer: The slope of the graph is distance divided by time, which gives the average speed of the beetle during that time interval.

Reading Skills MOVING BY FRICTION Friction is usually thought of as interfering with motion, but there are many sorts of movement that depend on friction. When any two surfaces move against each other, friction exerts force in a direction opposite to the direction of push. Runners use the energy in their leg muscles to push backward on the ground with one foot. The ground forces their body forward. If not for the friction between the running shoes and the ground, their feet would slip backward against the ground instead.

Reading Skills, continued MOVING BY FRICTION, continued The friction between two surfaces before they move is called static friction. After the two surfaces begin moving against each other, the frictional force lessens; the force is then called kinetic friction. Once a runner’s foot begins to slip, the frictional force decreases, as does the force exerted on the runner in the opposite direction—toward the finish line! Runners need friction to move forward.

Reading Skills, continued When a runner’s shoe slips against the ground, what is the effect on the net force affecting the runner? F. The net force pushing the runner forward increases. G. The net force pushing the runner forward decreases. H. The net force pushing the runner toward the ground increases. I. The net force pushing the runner toward the ground decreases.

Reading Skills, continued When a runner’s shoe slips against the ground, what is the effect on the net force affecting the runner? F. The net force pushing the runner forward increases. G. The net force pushing the runner forward decreases. H. The net force pushing the runner toward the ground increases. I. The net force pushing the runner toward the ground decreases.

Reading Skills, continued 7. A runner decides to get new running shoes because the old ones are slipping too much against the ground. What should the runner look for in a new pair of shoes?

Reading Skills, continued 7. A runner decides to get new running shoes because the old ones are slipping too much against the ground. What should the runner look for in a new pair of shoes? Answer: More friction with the ground is desirable, so the bottoms of new running shoes should have a rougher surface, and be less worn out, than the old ones.

Interpreting Graphics The graphic below shows four motorcycle racers on the last 800 m of a track. Use this graphic to answer questions 8 and 9.

Interpreting Graphics, continued 8. Assuming that each motorcycle continues to travel toward the finish line at the given constant velocity above, which will occur first? A. Cycle A passes Cycle B. B. Cycle B passes Cycle C. C. Cycle B crosses the finish line. D. Cycle D crosses the finish line.

Interpreting Graphics, continued 8. Assuming that each motorcycle continues to travel toward the finish line at the given constant velocity above, which will occur first? A. Cycle A passes Cycle B. B. Cycle B passes Cycle C. C. Cycle B crosses the finish line. D. Cycle D crosses the finish line.

Interpreting Graphics, continued From Cycle A’s frame of reference, which cycle or cycles are moving toward Cycle A the fastest? F. Cycle B appears to be moving the fastest. G. Cycle D appears to be moving the fastest. H. Cycles B and D appear to be moving at the same speed. I. All three cycles appear to be moving at the same speed.

Interpreting Graphics, continued From Cycle A’s frame of reference, which cycle or cycles are moving toward Cycle A the fastest? F. Cycle B appears to be moving the fastest. G. Cycle D appears to be moving the fastest. H. Cycles B and D appear to be moving at the same speed. I. All three cycles appear to be moving at the same speed.

Interpreting Graphics, continued The graph below shows how long it took for two vehicles to stop from a speed of 30 m/s. Use the graph to answer questions 10 and 11.

Interpreting Graphics, continued 10. What can we conclude from the graph about the car and the truck? A. The truck’s final velocity is greater than the car’s. B. The car’s final velocity is greater than the truck’s. C. The truck’s acceleration has greater absolute value than the car’s. D. The car’s acceleration has greater absolute value than the truck’s.

Interpreting Graphics, continued 10. What can we conclude from the graph about the car and the truck? A. The truck’s final velocity is greater than the car’s. B. The car’s final velocity is greater than the truck’s. C. The truck’s acceleration has greater absolute value than the car’s. D. The car’s acceleration has greater absolute value than the truck’s.

Interpreting Graphics, continued 11. If the slope of the two lines remained the same, how long would it take each vehicle to coast to a stop from an initial velocity of 100 mph?

Interpreting Graphics, continued 11. If the slope of the two lines remained the same, how long would it take each vehicle to coast to a stop from an initial velocity of 100 mph? Answer: Based on the slope of each line and the equation y = mx + b, the car would take 27 s, and the truck 40 s, to coast to a stop.