Acoustics? O Unit on the scale for sound intensity, abbreviated dB
The study of sound,
O Describes how humans perceive sound intensity
O Sound waves with frequencies above 20,000 hertz.

answer: the metamorphic rocks are formed when they are exposed to high pressure and high temperatures. this happens when one of the earth's plates comes in contact with the other plate by traveling in opposite directions, straight into each other or slipping under one another. the friction that is caused by this activity results in   melting of rocks and when it cools they are known as metamorphic rocks. this process needs a controlled amount of pressure and temperature otherwise it may turn into magma.