Center of Mass: Definition, 3D Calculation & Frame

[Dgonzo15]

What exactly is center of mass, and how do I calculate in three dimensions? Also, I need to know how to calculate it in three dimensions at relativistically high speeds?
Also, what do they mean by 'center of mass frame', as in the question "What are the energy and momentum in the center of mass frame?" Thanks.

 

[tiny-tim]

Hi Dgonzo15!

What exactly is center of mass, and how do I calculate in three dimensions?

oh come on, you can look this up!

look it up somewhere, and if you don't understand, copy it or link to it, and tell us which bit you don't understand

Also, I need to know how to calculate it in three dimensions at relativistically high speeds

instead of mvcosθ, you have to use mvcosθ/√(1 - v²/c²)

Also, what do they mean by 'center of mass frame', as in the question "What are the energy and momentum in the center of mass frame?"

it means using a coordinate system (a "frame") in which the centre of mass is stationary

 

[tom.stoer]

The c.o.m. frame is defined such that the total momentum P vanishes