This is because Newton refined Galileo's idea of inertia and created it as his first law of motion. Galileo stated that it was the propensity of things to resist changes in motion. Newton refined it by including: "Every thing continues in a condition of rest or uniform speed in a straight line except acted on by a nonzero net power".
I'm not sure what your question is. But, the half life is the amount of time required for half the material to decay. For U238 this is 4.5 billion years, whilst for Fr-223 (Francium) its about 22 minutes. To calculate the time for something to decay you need to use the equation:
Mass (after time t) = Mass (initial) * (0.5)^(time/half life)
Hope this helps
Scatter light doesn't reflect, reflect light goes off a mirror.
Now I can actually edit my answer directly: I'm fairly sure I've got this wrong, and my mind has gone blank for how to do it, if someone could delete this that would be great and I'll think about it and see if I can figure it out!
