All samples of an element are composed of atoms with the same
1. atomic mass
2. atomic number
3. # of nucleons
4. # of neutrons

All samples of an element are composed of atoms having the same number of protons. The number of protons determines its place on the periodic table and its atomic number. Therefore the atomic number is the amount of protons an element has contained within its nucleus. Elements can have various isotopes that each have a different mass. The answer is 1. atomic mass. 

Elias is almost correct. he just got it backwards.the correct answer is that it demonstrates elastic potential energy transforming into kinetic energy.