Related - Mach's principle: http://en.wikipedia.org/wiki/Mach's_principle http://en.wikipedia.org/wiki/Mach's_principle An important implication of relativity

Related - Mach's principle: http://en.wikipedia.org/wiki/Mach's_principle http://en.wikipedia.org/wiki/Mach's_principle An important implication of relativity is that when you push something, you do not change it's velocity. You change it's acceleration. It's a small but important distinction. Acceleration is more fundamental.