Physics Demo: Why Does 20 Pound Ball Fall Differently?

[drew102]

Ok so here is the situation: There is a 20 pound ball hanging from a string in a loop. below the ball, there is another identical string attached loosely in a loop. So here is what happens. A person puts a rod through the bottom loop and yanks really hard and the result is the bottom string breaks. However if you put the rod through the same loop at the bottom and then push really slowly the top sting snaps and the ball falls. Why does this happen?

 

[DyslexicHobo]

My physics teacher did this demonstration with my class as well. It has to do with the impulse-momentum equations, I think (F\DeltaT).

When the force is slowly increased, the top string obviously has more tension (whatever force is being applied plus the weight of the ball). When the force is increased very quickly, a large force is applied to a specific point on the ball and the tension does not have time to travel to the top?

...
...Maybe. I thought I knew, but maybe I don't. It's been so long since school!