In second year at "engines and motor vehicles" class.pompelmo wrote:manchild wrote:Noise level = difference between pressure in cylinder when ehxhaust valves open vs athmospheric pressure. That includes speed of opening of valves and diameter and lenght of exhaust as well as frequency/rpm.pompelmo wrote:I do not believe that's true...where have you heard that???

Every noise in the nature comes from pressure difference. For example; weapon silencers silence the sound of explosion by reducing the pressure and speed of gasses/pressure change. Same thing is with engine exhaust - aim is to reduce the pressure and to slow down the gasses before they reach the end of pipe (get in contact with atmosphere that will cause noise due to difference in pressure if one exists).
Noise from clapping doesn't comes because palms hit each other but because shape and speed of palms creates higher pressure zone between palms and once they hit each other noise appears as trapped air under pressure exits fast. Try hitting top of your palms to each other and there'll be no such noise because their shape traps almost no air.
