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25 Cards in this Set

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