How is Energy Dissipated in a Vacuum?

Most recent answer: 05/03/2013

Q:
Hi, If 2 identical metal objects (lets say cubes) were to collide at high speed in an inelastic collision in space or a vacuum, where would the kinetic energy go? The energy can't convert to sound, any heat energy couldn't be radiated away through the vacuum. Would the energy be released as UV heat or would the two objects heat up? Thanks!
- Chris I (age 20)
UK
A:

Hi Chris,

Heat energy in the form of electromagnetic radiation certainly can radiate through space (which is how the sun keeps the earth warm). In addition, unless the two objects had exactly equal and opposite momentum, they would have a net motion (and corresponding kinetic energy) after the collision.

Also, sound waves can propagate inside the two objects, whether or not they are in vacuum. Since these acoustic waves cannot radiate away from the object, this isn't a mechanism for energy loss. Rather, it is one of many routes by which the microscopic motions within the objects absorb the initial kinetic energy during the collision. In general, the inelastically colliding objects would heat up as the internal molecules were forced to vibrate and spin by the collision.

So the lost kinetic energy mostly goes to heat up the object, until it ultimately radiates away.

Cheers,
David Schmid


(published on 05/03/2013)