Unit 4

Rotational speed is the number of rotations per amount of time. If a lady bug was sitting any where on an LP, it would always have a rotational speed of 33 1/3 rpm.
Tangential speed depends on the radial distance, or the distance from the axis of rotation.
Real life applications of these concepts can be seen in train wheels and gears. Gears work by moving at the same tangential velocity and different rotational velocity. Train wheels self correct by having the same rotational velocity but different tangential velocity.

Rotational inertia is how resistant something is to rotation and it involves the distance from the axis of rotation. If there is a meter stick with two weights taped very near the middle, it would rotate easier because it would have a short distance to the axis of rotation and therefore a lower rotational inertia. If there is a meter stick with two weights taped towards the end, it would be more difficult to rotate because it would have a long distance to the axis of rotation and therefore a higher rotational inertia.

Conservation of angular momentum  means that the torques are equal in a situation such as a figure skater extending their arms and then curling up. When a figure skater is extended, she moves much slower than she does when curled up. Despite this, the angular momentum is the same before and after because when extended, the skater has a small rotational velocity and a large rotational inertia and when curled up, the skater has a large rotational velocity and a small rotational inertia.

Torque causes rotation. Torque = force x lever arm (distance from the axis of rotation). A large force, a large force, or both, create a large torque. For instance, if someone was having a hard time using a wrench, they should get a longer wrench because it would increase the lever arm and therefore create more of a rotation. When something is balanced, its clockwise and counter clockwise torques are equal.

The center of gravity is the average location of mass in an object. The base of support is like the bottom of a box or someone's feet. When the center of gravity is above the base of support, there is no torque/rotation. Lovering the center of gravity makes it more difficult to rotate the center of gravity outside of the base of support. Making the base of support lower creates more stability as well.

Centripetal force is an inward seeking force. For instance the moon stays in orbit around the earth because of the centripetal force pulling it to earth and the fact that it wants to keep going straight.