![]() Has gravity stopped exerting a force on them? If not, why don't they feel it? Gravity still exerts a force on them, but they don't feel it because their apparent weight has become zero. People falling from a high diving board feel weightless. How does the energy transfer in squeezing putty differ from that in squeezing a rubber ball? Putty converts the energy of the squeeze into thermal energy, whereas the rubber ball returns the energy to the hand. During rehabilitation after hand surgery, patients are often asked to squeeze and knead putty to strengthen their muscles. In what way does the string of a bow and arrow behave like a spring? The restoring force is proportional to the string's distortion. What type of friction causes bearings to not waste much energy? Static What does friction not depend upon? the area of contact Force and momentum are related in that: Force is a change in momentum per unit time As you come to a stop in your car, its momentum Is changed to zero because of external forces on the car. By what factor will its rotational kinetic energy change? It will decrease to 1/4 its original value. Suppose the time it takes for the moon to rotate doubles. When a spinning skater pulls in her arms: she decreases her rotational mass. Why can't you make the chair spin without touching something? Changing a system's angular momentum requires an angular impulse. If you sit in a good swivel chair with your feet off the floor, the chair will turn slightly as you move about but will immediately stop moving when you do. As you begin pedaling your bicycle and it accelerates forward, the forward force that the bicycle needs to accelerate is exerted by the ground on the tires. If you lift your feet in the air, then the weight of your feet produces a torque which helps your body rotate. When you pivot about your knees, your feet can actually help you lift your head and chest. How could you describe their angular position in terms of a reference orientation and a rotation? radians clockwise from north You can do push-ups with either your toes or your knees acting as the pivot about which your body rotates. ![]() The chairs in an auditorium aren't all facing the same direction.
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