The minimum energy required for an effective collision is called

Activation Energy

Explanation:

Effective collisions are those that result in a chemical reaction. In order to produce an effective collision, reactant particles must possess some minimum amount of energy. This energy, used to initiate the reaction, is called the activation energy.

the body's situation won't change the forces are equal opposit and on the same body

one "light year" is the distance that light travels, through vacuum, in one julian year.   that's 365.25 days, of 24 hours each.