If you cut a tree trunk into pieces, the resulting pieces and dust add up to the same mass as the original trunk. This is a demonstration of

The law of conservation of mass

Explanation:

The Law of Conservation of Mass dates from Antoine Lavoisier's 1789 discovery that mass is neither created nor destroyed in chemical reactions. In other words, the mass of any one element at the beginning of a reaction will equal the mass of that element at the end of the reaction.

answer; i believe the correct answer to the above question is ( friction)