Unit 5 Reflection

In this section, we studied centers of mass and gravity, angular momentum, torque, rotational velocity, and centripetal and centrifugal forces.

We first discussed centers of mass and gravity. We discussed how an object's centers of mass and gravity can be different, depending on the height of the object and the lever arm of each side. The torque, not the mass, of each side had to be in equilibrium to balance.

We discussed torque, which is the lever arm of an object, multiplied by its mass. If an object has a low mass, it can still have a higher torque than one with a large mass. To quote Archimedes, "give me a long enough lever, and a place to rest it on, and I can move the world."

Angular momentum is the momentum of an object moving in a circular path. The product of the mass multiplied by the radius multiplied by the velocity remains constant. This allows us to calculate how two of those figures change if one remains constant. For example, if the radius remains constant, the velocity and mass are inversely proportionate.

Rotational velocity is velocity in a circle. The magnitude of this velocity remains constant if no outside forces act on the object. However, the direction constantly changes. If it did not, the object would fly off in a path tangential to the circle.

Centripetal force is any force that pulls an object into the center of the circle. This may be tension, friction, or gravity. This keeps cans tied to strings going in circles, satellites in orbit, and cars in turns on the road.

Centrifugal force is not a real force. Instead, it is a term for an object's inertia causing the object to continue on its straight line path while being pulled into a circle. For more information, see the rotational velocity paragraph.

Torque And Center Of Mass Lab

Materials

1 meter stick

1 100-gram weight

A table (for use as a fulcrum)

Procedure

1. We measured the meter stick's center of mass without the weight. We determined that it was at the 49.5 centimeter mark.
2. We placed the 100-gram weight on the zero centimeter side of the meter stick and rebalanced it. The new center of mass was 29.4 centimeters.
3. The distance between the old center of mass and the new center of mass was the lever arm for the side without the weight. This lever arm was 29.4 centimeters.
4. The length from the new center of mass to the weight was the lever arm for that side. This was also 29.4 centimeters.
5. Since the lever arms were the same, the forces must have also been balanced to balance the meter stick on the fulcrum. Thus, the masses were the same, as the acceleration due to gravity is constant.
6. Since 50.5 centimeters of meter stick weighed 100 grams, then the meter stick must weigh 198.2 grams.