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!

 

[sir-pinski]

This phenomenon can be explained by the principles of inertia and momentum. When the person yanks the rod quickly, the bottom string experiences a sudden and strong force, causing it to break. However, when the rod is pushed slowly, the force is applied gradually and the top string has time to stretch and absorb some of the force. This causes the ball to remain suspended until the top string reaches its breaking point and snaps, causing the ball to fall.

Additionally, the weight of the ball plays a role in this demonstration. The 20 pound ball has a greater mass, which means it has a greater inertia and requires more force to move. When the rod is pushed slowly, the force applied may not be enough to overcome the ball's inertia, resulting in the top string breaking instead.

In summary, the difference in the speed and force applied to the rod, as well as the weight of the ball, all contribute to the different outcomes in this physics demonstration. It showcases the importance of understanding the principles of inertia and momentum in everyday situations.