A chemical change occurs when substances chemically react with one another. true or false

Light waves can move through , but they travel fastest when they move through a(n) .

Astring vibrates with a frequency of 10 hz. why can't a person hear the sound waves produced by the vibrating string, no matter how large the amplitude of the waves? out! this is homework and due tomorrow! you so much!

Describe at least two advantages and two disadvantages of using hydropower as a source of energy.