Did someone say physics!?
I like your thinking, but there are a couple significant mistakes in your analysis.
In order for the net to move, a shot (force) hitting the net's center of mass would have to overcome the initial static friction
Yes, this is true.
(which we can assume there is none due to the ice's slipperiness).
Coefficient of static friction for ice is certainly low, but definitely quantifiable http://iopscience.io...43C5E35A3EAC.c2
. If it were truly zero, then any amount of horizontal force applied to the net would set it in motion.
Essentially all there is then is to say that a horizontal force must exceed the downward force due to the mass of the net and gravity, in order for the net to move at all.
This is incorrect. Draw a free body diagram of the net. Downward gravitational force by itself will do nothing to resist horizontal motion of the net. It is only the force of friction that will resist the motion. We can assume a static coefficient of friction somewhere around 0.05 based on the article abstract I linked.
Friction Force = mass*acceleration of gravity * coefficient of static friction
Ffric = (56.69kg)*(9.81m/s2)*0.05 = 27.8 Newtons
Thus, the force of the puck needs to exceed 27.8 Newtons to be able to move the net.
I corrected the above calculations accordingly.
The hardest shot recorded is 105.4 mph = 47.12 m/s
The kinetic energy of a shot with this speed is KE = (1/2)*m*v2 = (1/2)*(0.17kg)*(47.12m/s)2 = 188.72 Newtons*m.
Yes, I'm with you.
In order to equate it to the Force applied, you must divide this number by the distance, which can be said from the top of the circle, is about 35 feet = 10.67 m.
No. Neglecting air resistance, no work is done while the puck is flying through the air. Work is done on the net only while the puck is making contact with it. So most of the kinetic energy is transferred to the net over a distance of a foot or so (however much the net stretches).
So (188.72 N*m)/(0.3 m) = 629 Newtons
. Corrected this calculation as well. The force exerted on the net is roughly 140 lbf, which seems pretty reasonable to me for a shot of that velocity.
I think it's perfectly reasonable that the net could move. However, it should be kept in mind that the assumptions for coefficient of friction and the distance over which the puck energy is transferred to the net are just ballpark estimates, and even slight changes to the values can drastically change the results. The other huge simplification of the problem is the transfer of puck energy to the net. In reality, it will not be linear. The force exerted will start very small as the puck first makes contact with the net. As the net stretches, tension in the strings will start to pull harder on the metal frame. The force exerted by the puck is growing, but at the same time its kinetic energy is decreasing since it is being slowed down. It is likely at a given point in time, the instantaneous force might be even higher than 140 lbf, but for most of the time the puck is in contact, the force would be significantly lower.
Edited by KillrBuckeye, 12 November 2010 - 04:25 PM.