No. This is just an experiment you can do with a video camera and a volleyball on a pole. And you don't really have to DO it anyway! Just do it as a thought experiment like Einstein would have done. Use a VERY thin pole and strike the volleyball perpendicularly to the outstretched string...
To Dr. Al:
You said:
My response to this remains the same: You are assuming conservation of angular momentum. I say it's not conserved in this case, because of the torque exerted by the rope.
But if you apply the law of conservation of angular momentum to the situation and if you use...
Mr. Zapper...
You said:
But mechanical energy cannot be conserved if L is conserved. This is because L has a linear dependence on angular velocity, while KE has a quadratic dependence on angular velocity. They cannot be satisfied simultaneously unless w=0 or 1.
There is an analogous...
In response to Dr. Al's answer:
The reason why the kinetic energy is twice as great is this: The moment of inertia becomes one half of the original while (according to the law of conservation of angular momentum) the angular velocity doubles. Now KE (rotational) is 1/2 I (omega)^2 So since...
To Dr. Al...
If there is no need for a mechanical energy source, then how do we account for the fact that at a later point in time, the kinetic energy of the volleyball is TWICE as much as it was at the beginning of the problem? That cannot happen without an energy source. (Or if it can...
Well, okay, but in the case of the person pulling the weights inward, the internal energy of the person is DECREASED by an amount equal to the increase of KE for the mases at the ends of his arms. In the case of the volleyball, where is the corresponding DECREASE of energy of the pole/string...
But I don't think that works. This string applied its force without outside influence. In every case that I can think of, some source of energy needs to be responsible for causing a rope to exert tension. For example, an electric or a gas motor can cause a tension in a rope which can then lift...
Mr. Zapper...
I think you misinterpreted my question. I understand fully that work is done by the tension in the string. And that the work done is Force times the distance. My question is, WHAT IS THE SOURCE OF THE ENERGY GIVEN TO THE VOLLEYBALL? I only gave it so much energy and the pole...
I'm afraid I need some help on this one. We are studying rotational dynamics and I read in my textbook, the explanation of a common classroom deonstration. A person sits on a rotating stool and holds heavy weights in their outstretched hands. Someone sets the individual into rotational motion...