Sunday, December 11, 2016

The Physics of a Slap Shot

One thing that has always fascinated me is just how hard a hockey player can hit a slap shot. In baseball, exit velocities on hits can reach up to 120 miles per hour, Giancarlo Stanton of the Miami Marlins pushed past that threshold to 123.9. By comparison, hockey slap shot has topped out at 108.8 miles per hour, thanks to the massive build of Bruins defenseman Zdeno Chara. This makes sense though, a baseball arrives at the plate anywhere from 75 to 105 miles per hour, and a bat swing can have high velocities near that too. So in the collision of the bat hitting the ball, there is a huge Impulse. In hockey though, a slapshot is usually launched from a standstill, or off of a soft, controlled pass. So I wondered, where does all of the energy come from in a slapshot?

SmarterEveryDay, a YouTube channel that focuses on these types of real world questions, helped to enlighten me on where all of this energy comes from. When a hockey player fires a slapshot, they don't hit the puck cleanly. If they were to do so, then the only energy that would be acting on the puck would be that applied by the player. Now, some of these hockey players are big dudes that can swing fast, but there's a maximum human threshold. In order to put more power behind the puck, one would have to look at the stick. Today, sticks are designed to have a certain amount of bend to them. This bend not only keeps the stick from breaking, but adds a whole new type of energy to the swing. Instead of hitting the puck clean off the ice, a hockey player will instead hit the ice first, which bends the stick back as much as a few inches, and then as they follow through, the generated elastic potential from the bending stick is unleashed on the puck, lengthening the collision, and exerting more energy. It all happens in a few milliseconds, but that momentary drag on the ice makes all the difference.

Check out the video here! It's really cool to watch for hockey and physics fans!

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