# Center mass acceleration

1. Jun 24, 2013

Hello, can someone explain to me what is the difference between center mass acceleration and angular acceleration? If i have an uniform disk laying still, then i give it a force to make it spin while it stays put. The angular acceleration obviously has a number. What about the acceleration of the center mass? Would this be zero since it is not moving?

2. Jun 24, 2013

### collinsmark

If the center of mass doesn't move (i.e., doesn't accelerate), it means that there must be at least one more force involved (besides the one that you give it yourself). This other force might be applied at the center of mass, or could be applied somewhere else on the disk, or could be the sum of one or more "other" forces. Whatever the case, if the center of mass of the disk does not accelerate, the vector sum of all forces involved add to zero.

I'll leave it to you to work out a couple of examples. What's the linear and angular accelerations if the "other" force is applied at the center of mass of the disk (for example, if the disk is on a stationary rotor shaft)? What is the linear and angular acceleration of the disk if the "other" force is an equal and opposite force on the opposite side of the disk?