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CapitalistBastard
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>>39887
Hockey pucks are frozen before games. Rubber is one of the most elastic materials on earth, and even vulcanization can't stop hockey pucks from bouncing. Smashed against a hard surface like concrete or ice, a puck rebounds with between 45 and 55 percent of its original velocity (less so on a softer surface like a board).
This percentage is the so-called "coefficient of restitution." In an ideal world, the puck wouldn't bounce off the ice at all. To minimize this unruly behavior, someone discovered a long time ago that freezing the puck before a game would make it slide better and bounce less, owing to its increased stiffness.
This can be demonstrated in a simple home experiment: place a puck in a freezer for an hour and then let it drop sideways on a concrete floor, along with a puck kept at room temperature. You will find that the cold puck bounces less than half the height of the warm puck.
In fact, they will bounce to about 12 percent and 27 percent of their original height, respectively. Note that a 50 percent velocity restitution versus a 25 percent height restitution for a warm puck is not a contradiction. This difference exists because the height at which the puck rises depends on its initial kinetic energy, which goes as v(2). So if we cut the puck's velocity by half, it comes back to 1/2 X 2=1/4 of its original height. For the frozen puck, the coefficient of velocity restitution is therefore on the order of 35 percent, as opposed to 50 percent for the unfrozen ones. This is why buckets of pucks are kept refrigerated during NHL games.
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