SM_chapter5 - 5 The Laws of Motion CHAPTER OUTLINE 5.1 The...

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Unformatted text preview: 5 The Laws of Motion CHAPTER OUTLINE 5.1 The Concept of Force 5.2 Newton’s First Law and Inertial Frames 5.3 Mass 5.4 Newton’s Second Law 5.5 The Gravitational Force and Weight 5.6 Newton’s Third Law 5.7 Some Applications of Newton’s Laws 5.8 Forces of Friction ANSWERS TO QUESTIONS Q5.1 (a) The force due to gravity of the earth pulling down on the ball—the reaction force is the force due to gravity of the ball pulling up on the earth. The force of the hand pushing up on the ball—reaction force is ball pushing down on the hand. (b) The only force acting on the ball in free-fall is the gravity due to the earth—the reaction force is the gravity due to the ball pulling on the earth. Q5.2 The resultant force is zero, as the acceleration is zero. *Q5.3 Answer (b). An air track or air table is a wonderful thing. It exactly cancels out the force of the Earth’s gravity on the gliding object, to display free motion and to imitate the effect of being far away in space. Q5.4 When the bus starts moving, the mass of Claudette is accelerated by the force of the back of the seat on her body. Clark is standing, however, and the only force on him is the friction between his shoes and the fl oor of the bus. Thus, when the bus starts moving, his feet start accelerating forward, but the rest of his body experiences almost no accelerating force (only that due to his being attached to his accelerating feet!). As a consequence, his body tends to stay almost at rest, according to Newton’s fi rst law, relative to the ground. Relative to Claudette, however, he is moving toward her and falls into her lap. Both performers won Academy Awards. *Q5.5 Shake your hands. In particular, move one hand down fast and then stop your hand abruptly. The water drops keep moving down, according to Newton’s fi rst law, and leave your hand. This method is particularly effective for fat, large-mass, high-inertia water drops. Q5.6 First ask, “Was the bus moving forward or backing up?” If it was moving forward, the passenger is lying. A fast stop would make the suitcase fl y toward the front of the bus, not toward the rear. If the bus was backing up at any reasonable speed, a sudden stop could not make a suitcase f ly far. Fine her for malicious litigiousness. *Q5.7 (a) The air inside pushes outward on each patch of rubber, exerting a force perpendicular to that section of area. The air outside pushes perpendicularly inward, but not quite so strongly. (b) As the balloon takes off, all of the sections of rubber feel essentially the same outward forces as before, but the now-open hole at the opening on the west side feels no force. The vector sum of the forces on the rubber is to the east. The small-mass balloon moves east with a large acceleration. (c) Hot combustion products in the combustion cham- ber push outward on all the walls of the chamber, but there is nothing for them to push on at the open rocket nozzle. The net force exerted by the gases on the chamber is up if the nozzle the open rocket nozzle....
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This note was uploaded on 11/09/2010 for the course PHYS 208 taught by Professor Smith during the Spring '10 term at CUNY City Tech.

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SM_chapter5 - 5 The Laws of Motion CHAPTER OUTLINE 5.1 The...

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