?DISCUSSION QUESTIONS (EVALUATION)If you toss a coin straight upward while riding in a

Aristotle on Motion What did Aristotle believe about the relative speeds of fall for heavy and light objects?

Aristotle on Motion Did Aristotle believe that forces are necessary to keep objects moving, or did he believe that, once moving, they would simply continue to move?

Galileo’s Concept of Inertia What idea of Aristotle did Galileo discredit with his experiments on balls rolling on a incline?

Galileo’s Concept of Inertia Which dominated Galileo’s way of extending knowledge: philosophical discussion or experiment?

Galileo’s Concept of Inertia What name is given to the property by which objects resist changes in motion?

Mass - A Measure of Inertia Which depends on location: weight or mass?

Mass - A Measure of Inertia Where is your weight greater, on Earth or on the Moon? How about your mass?

Mass - A Measure of Inertia What are the units of measurement for weight and for mass?

Mass - A Measure of Inertia A 1-kg object weighs nearly 10 N on Earth. Would it weigh more or less on the Moon?

Net Force What is the net force on a box that is being pushed to the right with 50 N of force while, at the same time, being pushed to the left with 20 N of force?

Net Force What two properties are necessary for a vector quantity?

The Equilibrium Rule Name the force that occurs in a rope when both ends are pulled in opposite directions.

The Equilibrium Rule How much tension is in a vertical rope that holds a 20-N bag of apples at rest?

The Equilibrium Rule What does \(\Sigma F=0\) mean? Text Transcription: Sigma F=0

The Equilibrium Rule One bowling ball sits at rest, and another bowling ball rolls down a lane at constant speed. Which ball is in equilibrium? Defend your answer.

Support Force Why is the support force on an object often called the normal force?

Support Force When you weigh yourself, how does the support force of the scale acting on you compare to the gravitational force between you and Earth?

The Force of Friction How does the direction of a friction force compare with the direction of the velocity of a sliding object?

The Force of Friction If you push to the right on a heavy piece of furniture and it slides, what is the direction of friction on the furniture?

The Force of Friction Suppose you push to the right on a heavy piece of furniture, but not hard enough to make it slide. Does a friction force act on the furniture?

The Force of Friction If you push a heavy piece of furniture and it slides at constant velocity, how much friction acts on it compared to your pushing force?

Speed and Velocity Distinguish between speed and velocity.

Speed and Velocity Why do we say that velocity is a vector and speed is not?

Speed and Velocity Does the speedometer on a vehicle show average speed or instantaneous speed?

Speed and Velocity How can you be both at rest and moving at 100,000 km/h at the same time?

Acceleration Distinguish between velocity and acceleration.

Acceleration What is the acceleration of an object that moves at constant velocity? What is the net force on the object in this case?

Acceleration What is the acceleration of an object in free fall at Earth’s surface?

ACTIVITIES (HANDS-ON APPLICATION) Your grandparents are probably interested in your educational progress. Perhaps, like many grandparents, they have little science background and may be mathematically challenged. Write a letter to them, without using equations, and explain the difference between velocity and acceleration. Mention that some of your classmates confuse the two, and include some examples that clear up the confusion.

ACTIVITIES (HANDS-ON APPLICATION) By any method you choose, determine your average walking speed. How do your results compare with those of your classmates?

ACTIVITIES (HANDS-ON APPLICATION) Place a coin on top of a sheet of paper on a desk or table. Pull the paper horizontally with a quick snap. What concept of physics does this illustrate?

ACTIVITIES (HANDS-ON APPLICATION) Place a file card on top of the mouth of a drinking glass. Place a coin over the center of the card. Snap the card horizontally so it flies off the glass. You’ll see that the coin drops into the glass. Doesn’t this illustrate the same physics concept as the preceding activity?

ACTIVITIES (HANDS-ON APPLICATION) Stand flatfooted next to a wall and make a mark at the highest point you can reach. Then jump vertically and make another mark at the highest possible point. The distance between these two marks is your vertical jumping distance. Use this distance to calculate your hang time.

These “plug-in-the-number” tasks are designed to familiarize you with the main equations that link the physics concepts of this chapter. They are one-step substitutions, much less challenging than the Think and Solve problems that follow. \(\text { Average speed }=\frac{\text { total distance }}{\text { travel time }}=\frac{\Delta d}{\Delta t}\) Show that the average speed of a rabbit that runs a distance of 30 m in a time of 2 s is 15 m/s. Text Transcription: Average speed=total distance/travel time=Delta d/Delta t

These “plug-in-the-number” tasks are designed to familiarize you with the main equations that link the physics concepts of this chapter. They are one-step substitutions, much less challenging than the Think and Solve problems that follow. \(\text { Average speed }=\frac{\text { total distance }}{\text { travel time }}=\frac{\Delta d}{\Delta t}\) Calculate your average walking speed when you step 1.0 m in 0.5 s. Text Transcription: Average speed=total distance/travel time=Delta d/Delta t

These “plug-in-the-number” tasks are designed to familiarize you with the main equations that link the physics concepts of this chapter. They are one-step substitutions, much less challenging than the Think and Solve problems that follow. \(\text { Acceleration }=\frac{\text { change of velocity }}{\text { time interval }}=\frac{\Delta v}{\Delta t}\) Show that the acceleration of a car that can go from rest to 100 km/h in 10 s is \(10 \mathrm{~km} / \mathrm{h} \cdot \mathrm{s}\). Text Transcription: Acceleration=change in velocity/time interval=Delta v/Delta t 10 km/h times s

These “plug-in-the-number” tasks are designed to familiarize you with the main equations that link the physics concepts of this chapter. They are one-step substitutions, much less challenging than the Think and Solve problems that follow. \(\text { Acceleration }=\frac{\text { change of velocity }}{\text { time interval }}=\frac{\Delta v}{\Delta t}\) Show that the acceleration of a hamster is \(5 \mathrm{~m} / \mathrm{s}^{2}\) when it increases its velocity from rest to 10 m/s in 2 s. Text Transcription: Acceleration=change in velocity/time interval=Delta v/Delta t 5 m/s^2

These “plug-in-the-number” tasks are designed to familiarize you with the main equations that link the physics concepts of this chapter. They are one-step substitutions, much less challenging than the Think and Solve problems that follow. Free-fall distance from rest; \(d=1 / 2 g t^{2}\) Show that the hamster in Exercise 37 travels a distance of 22.5 m in 3s. Text Transcription: d=1/2 gt^2

These “plug-in-the-number” tasks are designed to familiarize you with the main equations that link the physics concepts of this chapter. They are one-step substitutions, much less challenging than the Think and Solve problems that follow. Free-fall distance from rest; \(d=1 / 2 g t^{2}\) Show that a freely falling rock drops a distance of 45 m when it falls from rest in 3 s. Text Transcription: d=1/2 gt^2

THINK AND SOLVE (MATHEMATICAL APPLICATION) Find the strength of the net force produced by a 30-N force and a 20-N force in each of the following cases: (a) Both forces act in the same direction. (b) The two forces act in opposite directions.

THINK AND SOLVE (MATHEMATICAL APPLICATION) Lucy Lightfoot stands with one foot on one bathroom scale and her other foot on a second bathroom scale. Each scale reads 350 N. What is Lucy’s weight?

THINK AND SOLVE (MATHEMATICAL APPLICATION) Henry Heavyweight weighs 1200 N and stands on a pair of bathroom scales in such a way that one scale reads twice as much as the other. What are the scale readings?

THINK AND SOLVE (MATHEMATICAL APPLICATION) The sketch shows a painter’s scaffold in mechanical equilibrium. The person in the middle weighs 500 N, and the tension in each rope is 400 N. What is the weight of the scaffold?

THINK AND SOLVE (MATHEMATICAL APPLICATION) A different scaffold that weighs 400 N supports two painters, one weighing 500 N and the other weighing 400 N. The reading in the left-hand scale is 800 N. What is the reading in the right-hand scale?

THINK AND SOLVE (MATHEMATICAL APPLICATION) A horizontal force of 120 N is required to push a bookcase across a floor at a constant velocity. (a) What is the net force acting on the bookcase? (b) How much is the friction force that acts on the sliding bookcase? (c) How much friction force acts on the bookcase when it is at rest on a horizontal surface without being pushed?

THINK AND SOLVE (MATHEMATICAL APPLICATION) Driving along the road at 88 km/h, Reckless Rick runs into Hapless Harry, who is directly in front of him and is driving at 80 km/h. What is the impact speed - that is, the speed of the two vehicles the moment after collision?

THINK AND SOLVE (MATHEMATICAL APPLICATION) An airplane with an airspeed of 90 km/h lands on a run-way where the wind speed is 40 km/h. (a) What is the landing speed of the plane if the wind is head on? (b) What is its landing speed if the wind is a tailwind, coming from behind the airplane? (c) What would be the landing speed of the 90-km/h plane landing in a headwind of 90 km/h?

THINK AND SOLVE (MATHEMATICAL APPLICATION) (a) Show that the average speed of a tennis ball is 48 m/s when it travels the full length of the court, 24 m, in 0.5 s. (b) How would greater air resistance affect the travel time?

THINK AND SOLVE (MATHEMATICAL APPLICATION) (a) Show that Leslie’s average speed is 10 km/h when she runs to the store 5 km away in 30 min. (b) How fast is this in units of m/s?

THINK AND SOLVE (MATHEMATICAL APPLICATION) (a) Show that the acceleration is \(7.5 m/s^{2}\) for a ball that starts from rest, rolls down a ramp, and gains a speed of 30 m/s in 4 s. (b) Would its acceleration be greater or less if the ramp were a bit less steep? Text Transcription: 7.5 m/s^2

THINK AND SOLVE (MATHEMATICAL APPLICATION) Lillian rides her bicycle along a straight road at an average velocity v. (a) Write an equation showing the distance she travels in time t. (b) If Lillian’s average speed is 7.5 m/s for a time of 5.0 min, show that she travels a distance of 2250 m.

THINK AND SOLVE (MATHEMATICAL APPLICATION) Extend Table 1.2 (which gives values from 0 to 5 s) from 6 s to 10 s, assuming no air resistance.

THINK AND SOLVE (MATHEMATICAL APPLICATION) A car races on a circular track of radius r. (a) Write an equation for the car’s average speed when it travels a complete lap in time t. (b) The radius of the track is 400 m, and the time to complete a lap is 40 s. Show that the average speed around the track is about 63 m/s.

THINK AND SOLVE (MATHEMATICAL APPLICATION) A ball is thrown straight up with an initial speed of 30 m/s. (a) How much time does it take for the ball to reach the top of its trajectory? (b) Show that it will reach a height of 45 m (neglecting air resistance).

THINK AND SOLVE (MATHEMATICAL APPLICATION) A ball is thrown straight up with enough speed so that it is in the air for several seconds. (a) What is the velocity of the ball when it reaches its highest point? (b) What is its velocity 1 s before it reaches its highest point? (c) What is the change in its velocity, \(\Delta \mathrm{V}\), during this 1-s interval? (d) What is its velocity 1 s after it reaches its highest point? (e) What is the change in its velocity, \(\Delta \mathrm{V}\), during this 1-s interval? (f) What is the change in its velocity, \(\Delta \mathrm{V}\), during the 2-s interval from 1 s before it reaches the highest point to 1 s after it reaches the highest point? (Caution: We are talking about velocity, not speed.) (g) What is the acceleration of the ball during any of these time intervals and at the moment the ball has zero velocity? Text Transcription: Delta v

THINK AND SOLVE (MATHEMATICAL APPLICATION) A school bus slows to a stop with an average acceleration of \(?2.0 m/s^{2}\). Show that it takes 5.0 s for the bus to slow from 10.0 m/s to a stop. Text Transcription: ?2.0 m/s^2

THINK AND SOLVE (MATHEMATICAL APPLICATION) An airplane starting from rest at one end of a runway accelerates uniformly at \(4.0 m/s^{2}\) for 15 s before takeoff. (a) What is its takeoff speed? (b) Show that the plane travels along the runway a distance of 450 m before takeoff. Text Transcription: 4.0 m/s^2

THINK AND RANK (ANALYSIS) The weights of Burl, Paul, and the scaffold produce tensions in the supporting ropes. Rank, from greatest to least, the tension in the left rope in the three situations, A, B, and C.

THINK AND RANK (ANALYSIS) Rank, from greatest to least, the net force on the block in the four situations, A, B, C, and D.

THINK AND RANK (ANALYSIS) Different materials, A, B, C, and D, rest on a table. (a) Rank the materials, from greatest to least, by how much they resist being set into motion. (b) Rank the materials, from greatest to least, by how much support force (normal force) the table exerts on them.

THINK AND RANK (ANALYSIS) Three pucks, A, B, and C, are sliding across ice at the noted speeds. Air and ice friction forces are negligible. (a) Rank, from greatest to least, the force needed to keep the pucks moving. (b) Rank, from greatest to least, the force needed to stop them in the same time interval.

Aristotle on Motion Knowledge can be gained by philosophical logic, and also by experimentation. Which of these did Aristotle favor, and which did Galileo favor?

Aristotle on Motion Which of Aristotle’s ideas did Galileo discredit with his inclined-plane experiments?

Galileo’s Concept of Inertia A bowling ball rolling along a lane gradually slows as it rolls. How would Aristotle probably interpret this observation? How would Galileo interpret it?

Galileo’s Concept of Inertia A space probe is carried by a rocket into outer space. A friend wonders what keeps the probe moving after the rocket no longer pushes it. What do you say?

Galileo’s Concept of Inertia When a ball rolls down an incline, it gains speed because of gravity. When a ball rolls up an incline, it loses speed because of gravity. Why doesn’t gravity play a role when it rolls on a horizontal surface?

Mass - A Measure of Inertia What physical quantity is a measure of how much inertia an object has?

Mass - A Measure of Inertia Which has more mass: a 2-kg fluffy pillow or a 3-kg small piece of iron? Which has more volume? Why are your answers different?

Mass - A Measure of Inertia Is a person on a diet more accurately said to lose mass or to lose weight? Defend your answer.

Mass - A Measure of Inertia Personally, what is your mass in kilograms? Your weight in newtons?

Mass - A Measure of Inertia Gravitational force on the Moon is merely \(\frac{1}{6}\) the gravitational force on Earth. What would be the weight of a 10-kg object on the Moon and on Earth? What would its mass be on the Moon and on Earth? Text Transcription: 1/6

Net Force A monkey hangs stationary at the end of a vertical vine. What two forces act on the monkey? Which force, if either, is greater?

Net Force Suppose the monkey weighs 100 N and the vine supporting her pulls upward with a force of 120 N. What is the net force on the monkey? Describe her motion.

Net Force If the vine that supports the monkey breaks, what is then the net force on the monkey?

The Equilibrium Rule Can an object be in mechanical equilibrium when only a single force acts on it? Defend your answer.

The Equilibrium Rule When you push downward on a book that is at rest on a table, you feel an upward force. Does this force depend on friction? Defend your answer.

The Equilibrium Rule Nellie Newton hangs at rest from the ends of the rope as shown. How does the reading on the scale compare with her weight?

The Equilibrium Rule A hockey puck at rest is in equilibrium. Is it in equilibrium if it slides across ice at constant velocity? Defend your answer. Conceptual Physical Science, 6e Hewit

Support Force An empty jug of weight W is at rest on a table. What is the support force exerted on the jug by the table? What is the support force when water of weight w is poured into the jug?

Support Force Place a heavy book on a table, and the table pushes up on the book. A friend reasons that the table can’t push upward on the book because if it did, the book would rise above the table. What do you say to your friend? Why does this upward push not cause the book to rise from the table?

The Force of Friction In order to slide a heavy cabinet across the floor at constant speed, once it is sliding you exert a horizontal force of 550 N. Is the force of friction between the cabinet and the floor greater than, less than, or equal to 550 N? What happens to the cabinet if your push exceeds 550 N? Defend your answer.

The Force of Friction Consider your desk at rest on your bedroom floor. As you and your friend start to lift it, does the support force on the desk provided by the floor increase, decrease, or remain unchanged? What happens to the support force on the feet of you and your friend?

The Force of Friction In Figure 1.15 we see Marie pushing horizontally on a table that slides across the floor at constant velocity. If she pushed with the same amount of force, but directed that force downward a bit, how would the amount of friction of the table legs with the floor be affected? Defend your answer.

Speed and Velocity One ultralight aircraft travels due north at 100 km/h while another travels due south at 100 km/h. Are their speeds the same? Are their velocities the same? Explain.

Speed and Velocity What is the impact speed when a car moving at 100 km/h collides with the rear of another car traveling in the same direction at 98 km/h? What is the impact speed when they collide head on?

Speed and Velocity You’re in a car traveling on a highway at some specified speed limit. You see another car moving at the same speed directly toward you. How fast is the car approaching you, compared with the speed limit?

Speed and Velocity Emily Easygo can paddle a canoe in still water at 8 km/h. How successful will she be at canoeing upstream in a river that flows at 8 km/h?

Acceleration Gracie says acceleration is how fast you go. Alex says acceleration is how fast you get fast. They look to you for confirmation. Who’s correct?

Acceleration What is the acceleration of a Tesla automobile that maintains a constant velocity of 150 km/h?

Acceleration What is the acceleration of a car that moves at a steady velocity of 100 km/h for 100 s? Why is this question an exercise in careful reading as well as in physics?

Acceleration Correct your friend who says, “Japan’s bullet trains can easily round a curve at a constant velocity of 160 km/h.”

Acceleration Suppose that a freely falling object were somehow equipped with a speedometer. By how much would its speed readings increase with each second of fall?

Acceleration Consider a freely falling object dropped from rest. What is its acceleration at the end of 5 s? At the end of 10 s? Defend your answer (and distinguish between velocity and acceleration).

DISCUSSION QUESTIONS (EVALUATION) Asteroids have been moving through space for billions of years. A friend says that initial forces applied long ago keep them moving. Do you and your friend agree?

DISCUSSION QUESTIONS (EVALUATION) In answer to the question “What keeps Earth moving around the Sun?” a friend asserts that inertia keeps it moving. Correct your friend’s erroneous assertion.

DISCUSSION QUESTIONS (EVALUATION) Harry the painter swings year after year from his bosun’s chair. His weight is 500 N, and the rope, unbeknownst to him, has a breaking point of 300 N. Why doesn’t the rope break when he is supported as shown at the left? One day, Harry was painting near a flagpole, and for a change, he tied the free end of the rope to the flagpole instead of to his chair, as shown at the right. Discuss with your friends why Harry took his vacation early.

DISCUSSION QUESTIONS (EVALUATION) For the pulley system shown, what is the upper limit of the weight the strong man can lift?

DISCUSSION QUESTIONS (EVALUATION) When the strong man in Exercise 97 exerts a downward force of 900 N on the rope, how much upward force is exerted on the block?

DISCUSSION QUESTIONS (EVALUATION) In tearing a paper towel or plastic bag from a roll, discuss why a sharp jerk is more effective than a slow pull.

DISCUSSION QUESTIONS (EVALUATION) Someone standing at the edge of a cliff (as in Figure 1.24) throws a ball straight up at a certain speed and another ball straight down at the same initial speed. If air resistance is negligible, which ball will hit the ground below at greater speed? Or will they both hit at the same speed?

DISCUSSION QUESTIONS (EVALUATION) When a ball is tossed straight up, it momentarily comes to a stop at the top of its path. Is it in equilibrium during this brief moment? Why or why not?

DISCUSSION QUESTIONS (EVALUATION) Suppose that a freely falling object falls from a rest position and is equipped with an odometer. What equation is most appropriate for determining the distance fallen each second? Do the readings indicate equal or unequal distances of fall for successive seconds? Explain.

DISCUSSION QUESTIONS (EVALUATION) In the absence of air resistance, a ballplayer tosses a ball straight up. (a) By how much does the speed of the ball decrease each second while it is ascending? (b) By how much does its speed increase each second while it is descending? (c) How does the time of ascent compare to the time of descent?

DISCUSSION QUESTIONS (EVALUATION) On which of these hills does the ball roll down with increasing speed and decreasing acceleration along the path? (Use this example if you wish to explain to someone the difference between speed and acceleration.)

DISCUSSION QUESTIONS (EVALUATION) Because Earth rotates once every 24 hours, the west wall in your room moves in a direction toward you at a linear speed that is probably more than 1000 km per hour (the exact speed depends on your latitude). When you stand facing the wall, you are carried along at the same speed, so you don’t notice it. But when you jump upward, with your feet no longer in contact with the floor, why doesn’t the high-speed wall slam into you?

DISCUSSION QUESTIONS (EVALUATION) If you toss a coin straight upward while riding in a train that travels at uniform and steady motion along a straight-line track, where does the coin land? Where does the coin land if the train slows while it is tossed? Where does it land if the train rounds a curve?

DISCUSSION QUESTIONS (EVALUATION) Two balls, A and B, are released simultaneously from rest at the left end of the equal-length tracks A and B, as shown. Which ball, A or B, will reach the end of its track first?

DISCUSSION QUESTIONS (EVALUATION) Refer to the tracks in Exercise 107. (a) Does ball B roll faster along the lower part of track B than ball A rolls along the straighter track A? (b) Is the speed gained by ball B going down the extra dip the same as the speed it loses going up near the right-hand end-and doesn’t this mean that the speeds of balls A and B will be the same at the ends of both tracks? (c) On track B, won’t the average speed dipping down and up be greater than the average speed of ball A during the same time? (d) So, overall, does ball A or ball B have the greater average speed? (Do you wish to change your answer to Exercise 107?)