Momentum = mass x velocity
So both mass and velocity affect an object's momentum.
If the scientist repeats the experiment over and over and gets the same results. Also if the scientist peer reviews the experiment to make sure there is no bias in his or her results.
This is something I have no idea
Position and momentum.
This is Heisenberg's Uncertainty Principle:
Δx Δp ≥ h ÷ 4π, where Δx is the change in position, Δp is the change in momentum, and h is Planck's Constant.
