Physics: Relatively Speaking [Text Version]

Mechanics

Circular Motion

Circular motion. You don't know this, but you probably go through this a lot. You're driving around in your car, and you quickly make a turn. You may not notice, but you are actually increasing in acceleration. If you ever go into a culdesac (y'know one of those circle things at the end of a dead end?) and you circle around you would experience this. Well that's do to circular motion. Problem: A bicycle wheel rotates with a constant angular acceleration of 3.5 rad/s2. If the inital angular velocity of the wheel is 2.0 rad/s at t0 = 0, what angle does the wheel rotate in 2 seconds? Since we are given the angular velocity and the angular acceleration we use the 2nd equation. You should get 11 rad . . . or 630o Now find the angular velocity at 2 seconds! For this you can use the first equation. You should get 9.0 rad/s! Easy right!?!

Angular Velocity/Angular

Acceleration Imagine you have a turntable. It spins around. You watch as it spins. A piece of lint has gotten stuck to the outer rim. You observe as it goes round and round. You stop your turntable and notice where the lint stops. You start it up again but you stop the record after 10 seconds. You notice that the piece of lint has undergone 10 revolutions. Then you notice another piece of lint really close to the center of the record. You let the record play for another 10 seconds and realize that it had revolved around 10 times as well!!! Circular motion is measured in degrees or radians. Usually it is radians. You must use radians when performing your calculations. Here are some formulas that will help you out as you go along. Angular and Linear Quantity Relations These handy formulas let you convert from linear to angular back to linear again!!