In this video segment adapted from Shedding Light on Science, light is described as made up of packets of energy called photons that move from the source of light in a stream at a very fast speed. The video uses two activities to demonstrate that light travels in straight lines. First, in a game of flashlight tag, light from a flashlight travels directly from one point to another. Next, a beam of light is shone through a series of holes punched in three cards, which are aligned so that the holes are in a straight line. That light travels from the source through the holes and continues on to the next card unless its path is blocked.
This media asset was adapted from Shedding Light on Science.