system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If temperature is how fast atoms shake, how does absorbing a photon by black object cause it to shake harder than bouncing it back by white object?
gpt
You may have heard of the law of conservation of energy. Energy can never be created or destroyed. When the black object absorbs the photon, all of the kinetic energy is transferred to the object. Since the energy needs to go somewhere, it goes into heating the object, or causing the atoms to shake. 

But when the white object reflects it, the photon bounces off. If it is a perfect elastic collision, which essentially means the photon bounces off without losing any energy, the object shouldn’t gain any kinetic energy (shouldn’t heat up / atoms shake faster at all) this is because the photon still has its energy, so none has been transferred into object. 

In reality not all atoms are absorbed by black objects and not all are reflected by white objects, but on average more photons are reflected off the white ones rather than absorbed.