Resonance Tube Lab
Resonance 1 Williams Lab 1: Tube Staci Williams Kevin Schesing, Nicole Harty, Caitlin Kubota Section 015 2 Performed February 2, 2010 Due February 13, 2010 3 Theory: 2.1 Air As A Spring Williams Gas is a springy material, and when placed in a cylinder with pistons on each side it can be compressed as pistons push in, raising the pressure inside. There will be a net force from the pressure to push the piston back out. Since gas has mass it can support oscillations and waves. 2.2 Traveling Sound Waves in Air When a cone of a speaker moves out, it compresses air next to is and imparts an outward velocity to the air molecules around it, in addition to the random thermal velocities of air molecules. The molecules nearest to the speaker will collide with those near them and impart those molecules into motion, propagating away from the speaker producing sound. Similar statements apply to when the cone is moved in as well. If speaker cone vibrates sinusoidally, a traveling wave will be emitted form the speaker and the wave relation f = v < = wavelength, f = frequency of wave, v = velocity of wave> is satisfied. AS the motion of the wave molecules move along the direction of the propagation of the wave are called longitudinal waves, which is contrasting to transverse waves which are on strings. The waves as the elements of the string move transverse to the direction in which the waves travel. In traveling waves the displacement of air satisfies the wave equation. V = (P/) < v = velocity of wave, = specific heats at constant pressure/ " constant volume = Cp/Cv, P = air pressure, = air mass density>. With the ideal gas law it can be written as V = (RT/M ) < R = molar gas constant, T = absolute temperature, M = Molar mass>. For a given gas the speed will be proportional to the square root of the temperature giving the equation vrms = (3RT/M) < vrms ~ thermal speed of the gas molecules>. The speed of sound in gas is close to the thermal speed of molecules in gas, so the