Here is another favorite episode of Timeline...
Picture yourself at the beach watching the waves rise and break over the sand. You can see the water gather and rise as each waves comes in. Once a wave breaks the water level drops again. You watch the peaks and valleys rolls onto the beach. These waves transfer huge amounts of energy from one place to another traveling through the water and displacing it. We call this a mechanical wave because it needs to travel through a medium, in this case water. The number of waves that crash during a specific period of time is called the frequency.