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34. Circular Motion (Paul discusses his father working as a ticket collector in a merry-go-round and ties this to a Burl-Grey problem involving circular motion.) End Question: Here we see four possible paths, A, B, C, and D. What’s your take on this? When the marble rolls off the edge, will it follow path A — directly outward from the rotating record? Will it follow a curve, something like that of path B? Will it follow a straight line as shown in C? Or will it follow a tangent line as shown in D? |
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35. RR Wheels (Paul links the linear-rotational speed relation to an explanation of why railroad trains stay on tracks via tapered wheel rims.) End Question: If the pain of cups were fastened, not at their wide ends, but by their narrow ends, how would motion along the tracks be affected? |
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37. Centripetal
Force (Is the force that holds a can whirled overhead at the end of a string an outward-acting or inward-acting force — and why?) End Question: If instead of whirling a can through the air by a string, suppose we whirled it in a circular path on a horizontal friction-free lab table, in such a way that the string remains horizontal. Would the string tension alone, without vector components, be the centripetal force? |
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38. Centrifugal
Force (Paul discusses the forces experienced by bugs inside a horizontally-whirled can, and why centrifugal force is fictitious.) End Question: Using the equation for centrifugal force as a guide, what must occur for occupants of the ISS to no longer endure a weightless condition? Defend your answer. |
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39. Torque (We drop in on Paul’s class as he discusses the concept of torque.) End Question: If you use a pipe to extend the lever arm of the wrench, so your grip is 3 times as far from the bolt, and you pull twice as hard as before, at right angles to the pipe, by how much will the torque you produce increase? |
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40.
Balanced Torques (We drop in on Paul’s class as he discusses balanced metersticks and seesaws.) End Question: Suppose the boy succeeds by sitting on the far end after shifting the fulcrum beneath the one-quarter mark of the seesaw’s length as shown. At rotational equilibrium, how will the kid’s weight compare with the weight of the seesaw? |
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41.
Torques on a Plank (Torques on horizontal planks, taking center of gravity into account, are examined.) End Question: For the two-meterstick combination, at what centimeter mark of the horizontal meterstick should you place your finger for balance? |
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42.
Skateboard Torques (How does rotational physics explain how a skateboard is able to lift without external forces?) End Question: How do the upward curved surfaces of the ends of the skateboard enhance lifting? |
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43.
Angular Momentum (Conservation of angular momentum, with examples, including Paul in the classroom, are examined.) End Question: When you crawl toward the edge of the turntable, does its rotational rate increase, decrease, or remain unchanged? What physics principle supports your answer? |