Imagine a rock is dropped from the top of a tall building. after 2 seconds of falling, the rock's instantaneous speed is approximately 20 m/s.

The proton has a positive charge while the neutron has no charge they both make up the nucleus of the atom while the elections have a negative charge and surround the nucleus of the atom. the protons and electrons are used to calculate the atom's mass whereas the neutrons don't affect the mass