This text is meant to accompany class discussions. It is not everything there is to know about energy. It is meant as a prep for class. More detailed notes and examples are given in the class notes, presentations, and demonstrations linked below under unit resources.
Sometimes when "the speed of light" is reported it is not the speed of the photons being reported, but the AVERAGE SPEED of light from location "A" to location "B." Below is an animation showing this. As a photon travels from the left to the right in a piece of glass, it strikes many molecules and gets redirected. This takes time at every collision. In between collision with the molecules, the photon does travel at 3.00 x 108 m/s.