What is the meant by the frequency of a wave? what is the unit?

The frequency of a wave is the number of times the wave goes from peak to peak in a given unit of time the SI unit of frequency is Hertz (Hz) 1 Hz= 1 wave per second

1) when you rub your hands together quickly, the kinetic energy is converted to mechanical energy.2) thermal energy from the sun travels to earth as infrared waves.3) energy is transferred through the matter of space by electromagnetic waves. 4) when a match is burned, chemical potential energy is converted to thermal and radiant energy. 5) seismicwaves are caused by back and forth movement , or vibration, of an object. 6) mechanicalenergy in an engine changes thermal energy into kinetic energy to make a car move.