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25 Cards in this Set
- Front
- Back
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Which rolls faster down ramps -- hoops or disks?
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disks
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Why do disks always beat hoops when rolling down ramps?
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Disks have more rotational inertia (since the average location of the mass radius is shorter, no matter what size the disk)
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Does it matter how big or how massive a disk or hoop is when letting them race each other down ramps?
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No -- disks always beat hoops, no matter the size
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Rotational inertia is increased by increasing the ___ of the object or the ___ where it's located
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mass
radius |
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Why do tightrope walkers carry a long pole?
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The long pole has a large rotational inertia -- making it difficult to set in motion.
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What does it mean to have a large rotational inertia?
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It means that it's hard to set the object in rotational motion.
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How does a short pendulum swing compared to a long arm pendulum?
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The short one swings faster?
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Why do short pendulums swing faster than long ones?
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They have a smaller rotational inertia -- easier to set in motion.
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What effect does the mass of a pendulum bob have on the swing rate of a pendulum?
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No effect. Mass does not matter.
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If you double the length of a pendulum, the period of swing will be longer by what factor?
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about 1.4 times (square root of 2); T is proportional to root of length;
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What do we call the point around which all the mass of an object seems to be centered?
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Center of gravity
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When an object is set into rotation, it rotates around the ....
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center of gravity
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Does the center of gravity actually have to physically be in an object?
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No
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Where is the center of gravity of a doughnut?
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in the hole
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When you toss a tennis racket to someone, will the racket obey the rules of projectiles and follow a curved trajectory?
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Yes. The center of gravity is the one point that follows the trajectory.
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What must happen for an object to fall over?
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Center of gravity must extend beyond the support base -- not over the support base.
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If you hit an object exactly at the center of gravity, will it rotate?
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No. It will probably move, but it won't rotate.
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When a torque is applied perpendicularly to the side of football's tip, what will the ball do?
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It will rotate end over end.
(The ball has been kicked.) |
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Torque is defined as the ____ applied perpendicularly to an object times the ____ of rotation.
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force
radius |
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What are units for torque?
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N m [Newton-meter]
kg m^2 / s^2 |
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A force of 5 N applied perpendicularly to a wheel of radius 0.5 m has a torque of....
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2.5 N m
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If a torques of 5 N m and 3 N m are applied to one side of lever, then what torque must be applied to the other side of the lever?
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8 N m
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Why are doorknobs placed at the edge of a door than in the center of the door?
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Longer radius means that the force to move the door will be smaller.
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How do you find the center of gravity of an object?
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Balance on your finger. or...
Hang plumb bobs from 2 locations on the hanging object to see where the lines intersect. |
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Why do satellites, like our moon, not ever hit the earth if they are falling into each other?
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The curvature of the earth matches the fall rate of the satellites. [A tangent line to the earth be 8 km long would extend 4.9 m above the earth at it's far point. 4.9 m is the distance an object falls in 1 second.]
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