Let's look at the human hearing mechanism for a moment. It has a very wide dynamic range:
maximum for safe detection, without damage to ear delta-Pressure P ~ 2.8 x 10^(+1) Pascals minimum for detection delta-Pressure P ~ 2.8 x 10^(-5) Pascals
Can you figure out the amplitudes of motion of the air molecules in the following two sounds?
The typical human eardrum has a diameter of about 8 mm. In ordinary conversation, the pressure fluctuations on the membrane of the drum have an amplitude of about 0.028 Pascals.
Q: What is the magnitude of the fluctuations in the FORCE exerted on the eardrum in ordinary conversation? Q: Suppose we make a model of the eardrum by stretching a piece of plastic over the mouth of a bottle. In order to exert a similar force on this plastic, we place an object on the plastic, so its weight presses down. What is the mass of an object which will exert the proper force?
Fred's little brother Bobby is a real pain in the neck. He is always talking -- about baseball, comic books, Egyptian antiquities, flavors of ice cream -- he just won't be quiet. Fred decides to make the best of a bad situation: he builds a device to harness the power of Bobby's voice. A very thin panel 1 meter on a side converts the energy of the sound waves coming out of Bobby's mouth into electricity.
Q: Assume that Bobby talks at an ordinary volume, so the sound waves have a pressure amplitude of 2.5 x 10^(-2) pascals. Estimate the power this device will produce. Q: Could it light an ordinary bulb? Q: Fred builds a solar panel which is also 1 meter on a side and places it outside on a sunny day. Roughly how much power does this panel produce?