A beam is supported by two wheels, which are counterrotating "inwards" and cause opposite frictional forces given by
At the symmetrical position the two forces cancel each other. But if the beam is displaced by x0, the loads on the supporting wheels are different, which leads to a linear restoring force. i.e. to harmonic oscillations. Their frequency depends on the height h of the beam, the distance l of the wheels and the friction coefficient μ.
Use the applet to find the relation giving ω = ω(h, l, μ). Can you explain your result?