Forced Beam

This experiment was developed by Francis Moon to illustrate the complicated motion of a driven elastic beam. The beam is free at one end and periodically forced at the other end. As the frequency increases the beam passes through increasingly complex modes of oscillation, until for sufficiently large frequencies the motion is chaotic.

To get a better idea of how the beam is bending we attached a ultrathin piece of steel on the beam (viewable in the movie above) and setup a laser light on a tripod ointing at the reflective steel. The movie below shows the reflected image the laser makes. Not only can you see the torsional oscillations of the beam (the light would travers a straight line up and down if there were no twisting of the beam) you can also see what happens as we increase the forcing frequency!