Custom Physics?

I am working on a game which requires rapidly and drastically changing physics settings, I was wondering if it was possible to do this (somewhat easily) with scripting or if I would have to write a whole engine for every physics change.

A lot of these things can be done with unity. There are even Physic Materials which have special abilities. For example, you could assign a Metal material to your object. The object will bounce in a metal kind of way. And bullets will bounce in a metal kind of way as well.

This can be easily done by scripting, because you can set these settings by scripting on the fly. If you have more questions, please comment below and I will update my answer.

References:

You’d want to do this with Unity’s phsyics engine, which supports that sort of thing very easily. Coding your own engine would be both time-consuming and redundant. Also, check out this link: http://unity3d.com/support/documentation/ScriptReference/Rigidbody.html