COLD HARD SCIENCE: SLAPSHOT Physics in Slow Motion - Smarter Every Day 112

Hey, it's me Destin, welcome back to Smarter Every Day. So it might surprise you to know that we have hockey at the university that I went to. Anyway, today we're gonna talk about the physics of a slap shot. You're getting Smarter Every Day. [theme music] [crowd noise]

(Destin) No way, you're missing a tooth? That's so stereotypical hockey player. Can I see it? What did you, when'd you get your tooth knocked out?

• 3 years ago.

• 3 what?

• 3 and a half years ago.

• That's awesome dude. Is it like a right of passage that you have to lose a tooth in order to play hockey?

• No I mean.. ah..

• Just the good players?

• Just the good ones.

• [laughs] Alright so here's what we're gonna do today. We're gonna hit the puck and record it with a Phantom which I have setup over there, and we're gonna see exactly what's happening. I've heard that you don't actually hit the puck first, but I want to look at the dynamics of how that happens. But first, let's look at your stick here. What kind of stick is it, is it a wooden stick?

• No, it's a one piece composite.

• Yep

• Made out of graphite. So mine's an 85 flex. I like mine a little whippier.

• Whippier is 85.. I love that word. Can you say that as much as possible during this interview?

• Yeah, I can say it. A little more whip to it. You can get a stiffer one for the bigger guys.

[hits puck]

(Destin) I don't understand how you can hit that hard. That's crazy, I respect goalies a lot more now. OK, let's get the Phantom. Hoo, I've fallen! [laughs]

(Destin) Alright, bring it. [hits puck] [hits ice] [hits puck] [hits ice] [hits puck]

OK, so we got the close-up shot. Now what we're gonna do is we're gonna transition to a wide shot. We're gonna keep the Phantom at 3,200 frames per second but the goal here, the data we're looking for is we're gonna try to pre-load that stick and get the entire flex, or the deformation of the stick while he goes in for the slap shot. The slap shot is the fastest shot in hockey.

So what's the advantage of having a flexible stick? Let's check out the high speed. The player stores potential energy in the stick by striking the ice before he hits the puck. Now this seems like it would waste energy and slow down his shot but it actually does the opposite. By gradually releasing that potential energy stored up in the stick like a slingshot, the player can make the puck go even faster than he can swing the stick. Look at the overflex here as the stick outruns the player's hands.

[hits puck]

This means that a good slap shot is all about timing. And not just the timing about where you're gonna hit the ice, but also knowing how long it takes that stored up energy to whip out of your stick.

So to understand the flexibility of a hockey stick we're here with my friend Dr. Jeff Evans. We are friends, correct? Can I say that?

• We are friends.

• We are friends. I once tried to convince him to shoot a coyote in his pasture cause I thought.. no, it wasn't a coyote.

• We thought it was.. he thought it was a coyote. It was a donkey.

• It was a.. [laugh] It was a donkey.

You break things right?

• We do. We break things by pushing, pulling, twisting, fatigue, we wear them out, we break them.

• OK, some bonus footage. We're going to crush a hockey puck here. Check it out. 80,000lbs on a hockey puck. One interesting thing I discovered while doing this is hockey players often have no idea what the flex number on their stick means. If you support a stick on both sides here and you hang weights right on the center, that flex number that's on every single hockey stick is an indication for how much weight it takes to deflect a hockey stick one inch.

The problem is, often manufacturers don't do it correctly so we have all these sticks from different manufacturers and Dr. Evans is gonna take the data as I apply weight to the stick and we're gonna measure the actual flex number against the claimed flex number.

We hung calibrated weights from four different sticks, each with a different flex number. Then we recorded the deflection values for each stick and generated a curve representing its stiffness. The flex value is the weight in pounds required to deflect the stick one inch. The numbers we measured however were much lower than the manufacturer's numbers but this is probably because the sticks were used and they lost their stiffness over time.

Check it out though. Real science. Let's take a closer look though. A beam deflection equation can be used to model a hockey stick's flex. This force represents the pivot hand and this force represents the stick hitting the ice. The maximum displacement happens right here in the middle where the player's hand pushes on the stick.

In engineering we use two types of diagrams called shear and moment diagrams to understand the stresses on the inside of a beam. So if our hockey player is strong enough to actually break a stick while doing a slap shot, according to science, where exactly along the stick is it going to break?

[hits puck]

• Did you get it?

(Destin) So where do you think it broke relative to where your hand was?

• Probably in it.

• Like you think it was in your hand when it broke?

• Yeah. Oh yeah.

• Alright, let's make sure I got it on slow mo.

[hits ice] [scrapes ice] [hits puck]

Did you see that? There are two types of loading that added up to break the stick. First he flexed it on the ice, but it wasn't until he tried to actually accelerate the puck that it kicked it up over its maximum stress limit and actually broke the stick. That is awesome.

So thanks for sticking with me as I try to explain a sport I don't truly understand. If you'd like to help with Smarter Every Day and help me do crazy stuff like this, you can support the sponsor which is audible.com. Go to audible.com/smarter, you can get a free audio book. They've got thousands to choose from, get whatever you want. You can do a free trial, free book free trial, you can download it and listen to it and if you don't like it you can return it and get another one. It's a pretty good deal.

Anyway, I used it long before they asked to sponsor Smarter Every Day so I'm more than happy to suggest it to you. audible.com/smarter, I get credit for you checking out Audible, and it helps Smarter Every Day move forward and do more crazy stuff.

Anyway, I'm Destin, you're getting Smarter Every Day. Thank you very much, have a good one.

Before... and after.

• It was a smashing good time.

• [laughs] You want more whippyness, or more stiffyness?

• Oh, ah all in, all in.. All in preference.

• [laugh] - It's for science. I need a new stick.

• [laughs] [hits puck, hits wall] [laughs]

[Captions by Andrew Jackson] captionsbyandrew.wordpress.com Captioning in different languages welcome. Please contact Destin if you can help.