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Collisions on the Ice

So how much force is generated in a check? Using a mathematical formula, we can discover how much energy is expended in an open ice hit. Let's say it's late in the third period at the San Jose Arena with the Sharks ahead of the Philadelphia Flyers by one goal. Flyers captain Eric Lindros, deep in his team's zone, finds himself alone with the puck, facing a sea of ice. There is only one man who could possibly stop him from breaking away at the goalkeeper--Sharks forward Jeff Friesen. As Lindros goes into in high gear to tie the game, Friesen decides not to lay back and play it safe, but to rush forward at full speed and perhaps take out the Flyer forward by hitting him straight on. With Lindros weighing in at 6-4, 230 lbs. and Friesen at 6-0, 200 lbs., the fans may want to prepare for a small earthquake in the Arena. Just how much energy results from this collision?

   Eastern Conference

Western Conference

  Weight lbs. (select above)

 Speed in mph

 Weight lbs. (select above)

 Speed in mph

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Energy Produced:
The amount of energy produced from the collision is equal to Joules. This collision produces enough energy to shoot a puck feet. The puck would initially be moving at a speed of mph. The stopping force is pounds. This is enough energy to light a 60 watt lightbulb for seconds.

checking sequence
This sequence shows a check along the boards, which is much more common than an open ice hit. The math is similar but you'd need to factor in the boards.

In our calculations, we'll assume that the players become entangled and "stick" to each other during the collision. This is called an inelastic collision. Even though the players may not come to a complete stop (depending on their weights and speeds), we can still calculate the amount of energy that will be dissipated in the collision. We do this by calculating the energy of each player before the collision, and subtract the energy of the combined players after the collision. The kinetic energy of each player before the collision can be calculated with the equation:

Energy = (1/2)mass x velocity 2

The energy after is:

Energy = (1/2)total-mass x final-velocity 2

To find the final velocity, you use the fact that the initial momentum (mass x velocity) of both players must equal the final momentum of the players:

(mass player 1 x velocity player 1) + (mass player 2 x velocity player 2) = combined mass x final velocity

Notice that in the above equation we know all the variables except for the final velocity. We solve for this and get:

  final velocity =   [(mass player 1 x velocity player 1) + (mass player 2 x velocity playe r2)]
  combined mass

The energy comes out in a metric unit called a "joule". A joule is not a lot of energy. It's about the amount of energy you'd use to lift an apple to the height of your waist (1 meter).

To find the stoping force, we assumed the collision between the players took about 1/4 of a second. Knowing this, we can look at the change in momentum of either player and use the formula:

force = change-in-momentum
time of impact

According to Newton's third law -- for every action there is an equal and opposite reaction -- each player must experience the same force.

To calculate the time a lightbulb burns, all you need to know is that when you use one joule per second, that's one watt. We divided the final energy by 60 to calculate the time in seconds.

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