[animation of waves moving around a tuning fork, narrator speaking:]When an object vibrates, it disturbers the air molecules around it. The molecules carry the energy of the sound in all directions. The sound travels out as waves. [video of waves in water] Think of a wave in water. If we drop a pebble into a pond the waves move out from where the pebble hit the water. Sound travels in waves, but in all directions. [animation of tuning fork -with molecules moving around ]Here is a tuning fork. When we strike it, it gives off a certain tone. If we could see what was happening, it might look like this. The tuning fork is vibrating. As the prongs move out they push against the air molecules around them. The molecules push together, which is called compression. Then there are places were the molecules are spread out between the compressions. This spread out area is called rarefaction. The whole sound waves travel as a longitudinal wave. [video of girl striking tuning fork] So the sound is carried by compressing some molecules and leaving areas between the compressions with fewer molecules.

[boy experimenting with slinky on table] Here is another example of this idea. The slinky is pulled and held across the floor. When we pull together some of the slinky’s sections, and then let it go, notice that it travels the length of the slinky, with areas of compression, and rarefaction.