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16 Cards in this Set
- Front
- Back
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rotational inertia
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that property of an object that measures its resistance to any change in its state of rotation: If at rest, the body tends to remain at rest; if rotating, it tends to remain rotatin and will continue to do so unless acted upon by a net external torque
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Torque
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The product of force and lever-arm distance, which tends to produce rotation. Torque =lever arm X force
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center of mass
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the average position of mass or the single point associated with an object where the force of gravity can be considered to act.
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center of gravity
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the average position of weight or the single point associated with an object where the force of gravity can be considered to act
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centripetal force
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a center-seeking force that causes an object to follow a circular path
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centrifugal force
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an apparent outward force due to rotation, experienced in a rotating frame or reference. It is fictitious in the sense that it is not part of an interaction, but is an apparent force in itself- a result of rotation-with no reaction-force counterpart
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angular momentum
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the product of body's rotational inertia and rotational velocity about a particular axis. For an object that is small compared with the radial distance, it is the product of mass,speed, and radial distance of rotation.
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conservation of angular momentum
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When no external torque acts on an object or a system of objects, no change of angular momentum takes place. Hence, the angular momentum before an event involving only internal torques is equal to the angular momentum after the event.
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When your whirl a can at the end of a string in a circular path, what is the direction of the force that is exerted on the can?
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If we whirl a tin can on the end of a string, we find that we must keep pulling on the string-- exerting a centripetal force. The string transmits the centripeta force, which pulls the can into a circular path.
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Is it an inward force or an outward force that is exerted on the clothes during the spin cycles of an automatic washer?
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In its spin cycle, the tub rotates at high speed and produces a centripetal force on the wet clothes, which are forced into a circular path against the inner wall fo the tub. The tub exerts great force on the clothes, but the holes in the tub prevent the exertion of the same force on the water in the clothes and the water escapes. Strictly speaking the clothes are forced away from the water; the water is not forced away from the clothes.
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If the string that holds a whirling can in its circular path breaks, what kind of force causes it to move in a straight-line path- centripetal,centrifugal,or no force? What law of physics supports your answer?
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No force acts on it
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If you are not weating a seat belt and you slide across your seat and slam against a car door when the car rounds a curve, what kind of force is responsible - centripetal, centrifugal, or no force? support your answer
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no force because there is no centripetal force holding us in circular motion (ie seatbelts)
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distinguish between linear momentum and angular momentum
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Just as an external net force is required to change the linear momentum of an object, an external net torque is required to change the angular momentum of an object. We can state a rotational version of Newton's first law (the law of intertia) An object or system of objects will maintain its angular momentum unless acted upon by an unbalanced external torque
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What is the law of inertia for rotating systems in terms of angular momentum?
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In the absense of an unbalanced external torque the angular momentum of that system is constant. This means that the product of rotational inertia and rotational velocity at one time will be the same as at any other time.
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What does it mean to say that angular momentumis conserved?
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conservation of angular momentum when the man pulls his arms and the whirling weights inward, he decreases his rotational inertia l, and his rotational speed correspondingly increases
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If a skater who is spinning pulls her arms in so as to reduce her rotational inertia to half of what it was, by how much will her angular momentum increase? By how much will her rate of spin increase? (why are your answers different?)
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This procedure is used by a figure skater whos tarts to whirl with her arms and perhaps a leg extended and then draws her armas and leg in to obtain a greater rotational speed. Whenever a rotational body contracts, its rotational speed increases.
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