When we push something it moves due to the disturbance in it's molecular arrangement causing waves. How do I calculate the speed of push/waves? http://www.youtube.com/watch?v=Dnv-Pm4ehFs The push actually depends on the amount of the force applied, right? That is, the push is force dependent, so how does he state the magnitude of it?
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2$\begingroup$ Look up "speed of sound". $\endgroup$– Olin LathropCommented Jun 26, 2013 at 13:38
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1$\begingroup$ the speed of "push" or a longitudinal wave depends upon the medium's properties such as tension, density etc. and not on the force applied. $\endgroup$– udiboy1209Commented Jun 26, 2013 at 14:20
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$\begingroup$ then how come in the video he precisely stated the magnitude of the push $\endgroup$– gksinghCommented Jun 26, 2013 at 14:28
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$\begingroup$ Also a tansverse effect travels with longitudinal one. Like a polaron moving. If you push faster than the actual push speed(relative to bulk), it breaks right? $\endgroup$– huseyin tugrul buyukisikCommented Jun 27, 2013 at 12:15
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1 Answer
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To get an idea calculate the solid wave speed $c = \sqrt{\frac{E}{\rho}}$ where $E$ is the modulus of elasticity and $\rho$ is the density.
The actual wave speed is different, but this when get you close enough for what you want.
Example
Steel with $E=2\cdot 10^{11} \; {\rm N/m^2}$ and $\rho = 7680 \;{\rm kg/m^3}$ has wave speed
$$ c = \sqrt{\frac{2\cdot 10^{11}}{7680}} = 5103\; {\rm m/s} $$
answered Jun 26, 2013 at 18:18