How Fuel Cells Work. Polymer Electrolyte Membrane (PEM) fuel cells used in automobilesâalso called Proton Exchange Membrane fuel cellsâuse hydrogen fuel and oxygen from the air to produce electricity. The diagram and animation below show how a PEM fuel cell works.
Sound is what happens when you transmit vibrations of energy through that matter. Sound is made up of wave vibrations. When you talk aloud, the motion of your vocal cords causes the air to vibrate. Air is made up of molecules, and as those air molecules vibrate, they hit each other.
Sound and noise are often used interchangeably for anything perceived by means of hearing. Sound, however, is more general in application, being used for anything within earshot: the sound of running water. Noise, caused by irregular vibrations, is more properly applied to a loud, discordant, or unpleasant sound: the noise of shouting. Tone is applied to a musical sound having a certain quality, resonance, and pitch.