Hinged rigid beam vs mass free fall

AI Thread Summary
The discussion centers on a foam cushion drop test where a 50 kg mass on a hinged platform separates from the platform upon dropping the raised end. This observation raises questions about the principles of free fall, particularly the independence of mass in acceleration. The phenomenon is explained through the concept of torque and angular acceleration, revealing that parts of the rod beyond a certain point experience vertical acceleration greater than gravitational acceleration. The calculations indicate that the angle of the rod affects the acceleration of points along its length. The findings highlight the complexities of motion in hinged systems compared to free-falling bodies.
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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:
 
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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
 
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