As the soldiers walk onto the sand they slow down and so
each line of soldiers bends. They end up moving in a different direction. (See Figure 1). The
same thing would happen with an unpowered car or truck rolling from the tarmac onto the
Now think about a beam of light travelling through air and then hitting a block of glass at an angle. The light slows down when it enters the glass. It also changes direction.
When a beam of light hits the glass at an angle the side that hits the glass first slows down first and so the whole beam slews round, changing direction just like the group of soldiers. We call this change of direction refraction. You can see this in Figure 2.
The bigger the change of speed the more the light will refract. Light moves slower in diamond than it does in glass and so there will be more refraction when a beam of light moving in air hits a diamond than if it hit a piece of glass at the same angle.