Standing passengers on trains often hold on to rails or handles because as the train starts and stops their bodies want to stay at rest or in motion. This is all due to a
Newton's 3rd Law of motion that for every action there is an equal and opposite reaction
b
Newton's 2nd Law of motion that an object at rest stays at rest or in motion until acted on by an unbalanced force
c
Newton's 1st Law that an object in motion stays in motion and an object at rest stays at rest until acted on by an unbalanced force
d
Newton's 1st Law that motion only exists in friction less environments.