SOUND

Sound waves with a greater amplitude have a greater intensity.The intensity of a sound is measured in units of decibels (dB).Pitch is the human perception of the frequency of sound.

Sounds are made when objects vibrate. The vibration makes the air around vibrate, and the air vibrations enter your ear which you hear as sound. You cannot always see the vibrations, but if something is making a sound, some part of it is always vibrating.

Echolocation is the process of locating objects by bouncing sounds off them.

Doppler Effect is the shift in frequency and wavelength of waves which results from a source moving with respect to the medium, a receiver moving with respect to the medium, or even a moving medium.