# Hinged rigid beam vs mass free fall

1. Sep 24, 2014

### CraigHyattOB

Our test group had some issues with an ASTM foam cushion drop test, and I was asked to investigate. I fixed the problem, but noticed something in a high speed video. A 50 kg mass on the hinged platform separates from the platform when the raised end of the platform is dropped. I thought the old cannon balls dropped from the Tower of Pisa story says acceleration in free fall is independent of mass. Why does the free end of the platform accelerate faster than the mass? I duplicated the effect with a ruler and steel nut:

2. Sep 25, 2014

### sk9

Acc. is same for free falling bodies. Take torque about the stationary end of the rod and find angular acc.
$\alpha = \frac{3g\cos\theta}{2l}$​
Here $\theta$ is the angle with horizontal of rod, so any point on the rod beyond $\frac{2l}{3g\cos^2\theta}$ will have vetical acc. more than g . So it is somewhere here that you are placing the nut.
Hope that helps

3. Sep 25, 2014

Thanks!