Why is it believed that force is the cause of motion,How does that compare to Einstein's law of motion?

Answer 1

f=ma
1st thing is it Einstein's law of motion or new ton's any way:

we kw that
a=v/t^2

and E=mc^2

c is velocity~~ square of speed of light

nw compare the two!

without any source of force there is absolutely no motion!
but a substance suppressing or stoping motion occurs when an equal and opposite force is applied!