The change in frequency of a wave as its source moves in relation to an observer. A)
Ultrasound
B)
Frequency
C)
Doppler Effect
D)
Echo

I don’t know
i’m giving people free points so please don’t report ;(

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.