Particles with a spin of 0, 1, or 2 move force from one particle to another. Some examples of these particles are "virtual gravitons" and "virtual photons". Virtual gravitons have a spin of 2 and they represent the force of gravity. This means that when gravity affects two things, gravitons move to and from the two things. Virtual photons have a spin of 1 and represent electromagnetic forces (or the force that holds atoms together).