OT: XKCD - Knocking a goalie backward with a puck

[PricePkPatch*]

XKCD is a webcomic about romance, sarcasm, math, and language. It has been mostly known for producing interesting Maps of the Internet (and a 2nd iteration years later). The creator also drew up movie narrative charts as well as a map of our solar system's gravity wells.

Admittedly, it's pretty geeky and sciency. The author, Randall Munroe is also an enthusiast researcher who likes answering funny hypothetical questions about science in his "What If" page. The first one of these "What If" was: What would happen if you tried to hit a baseball pitched at 90% the speed of light?, it's an entertaining and relatively accessible read.

Now; his most recent What If is: How hard would a puck have to be shot to be able to knock the goalie himself backwards into the net?. I thought a few people would have a blast reading it.

Click to read more...

 

[ZARTONK]

Your post on playing on an inclined plane made me think about this, but before I could answer back that thread was closed down.


How about having a game on a huge seesaw?

Behold my MS paint skills!

The difference of weight on each side will affect the inclination of the rink.

 

[Brainiac]

Your post on playing on an inclined plane made me think about this, but before I could answer back that thread was closed down.

How about having a game on a huge seesaw?

The difference of weight on each side will affect the inclination of the rink.

1-Trade for big Buff,
2-Tell him to stay in the opponent's zone whatever happens.
3...
4-Win!

 

[PricePkPatch*]

1-Trade for big Buff,
2-Tell him to stay in the opponent's zone whatever happens.
3...
4-Win!

Wouldn't work, he would be offside half the time.. And if he stands on the blueline, he's not gonna have enough leverage to influence the equilibrium..

.... man, it would change the dynamics of icing..

 

[Stags209]

I worked the problem out myself and found a value slightly more realistic than M=8.0, though I guess it depends on what constitutes "knocking a goalie backwards". For my calculations I counted an acceleration of only 1 m/s^2 as moving the goalie backwards.

Using his statement that "if you slowly tilt a hockey rink, it could get up to 50 degrees before the players would all slide to one end", I calculaed the coefficient of static friction of blades with the ice. With the assumption that a goalie weighs 99 kg, I got u,static=1.192. From there I can calculate the forces on the goalie from a shot.

Fx,sum=0=u,static*g*m,goalie-m,puck*a,puck m,puck=.165 kg
than you can solve for the acceleration of the puck and find it is 7016.4 m/s^2!

I then assumed the shooter was 5 meters away from the goalie.

s(t)=a,o(t-t,o)^2/2+v,o(t-t,o)+s,o 5m=7016.4m/s^2(t)^2/2+0+0 solving for t you get t=0.0378 sec.

Finally,

v(t)=a,o(t-to)+v,o=7614.4(.0378)+0 = 287.8 m/s= 643.83 MPH.

M=V/c=287.8/sqrt(1.4*287kj/kgK*286K)=0.85.

So not quite supersonic, but that is to just get the goalie to move backwards. He probably assumed knocking back meant actually launching the goalie backwards.

That would hurt a lot I imagine

 

[PricePkPatch*]

I worked the problem out myself and found a value slightly more realistic than M=8.0, though I guess it depends on what constitutes "knocking a goalie backwards". For my calculations I counted an acceleration of only 1 m/s^2 as moving the goalie backwards.

Using his statement that "if you slowly tilt a hockey rink, it could get up to 50 degrees before the players would all slide to one end", I calculaed the coefficient of static friction of blades with the ice. With the assumption that a goalie weighs 99 kg, I got u,static=1.192. From there I can calculate the forces on the goalie from a shot.

Fx,sum=0=u,static*g*m,goalie-m,puck*a,puck m,puck=.165 kg
than you can solve for the acceleration of the puck and find it is 7016.4 m/s^2!

I then assumed the shooter was 5 meters away from the goalie.

s(t)=a,o(t-t,o)^2/2+v,o(t-t,o)+s,o 5m=7016.4m/s^2(t)^2/2+0+0 solving for t you get t=0.0378 sec.

Finally,

v(t)=a,o(t-to)+v,o=7614.4(.0378)+0 = 287.8 m/s= 643.83 MPH.

M=V/c=287.8/sqrt(1.4*287kj/kgK*286K)=0.85.

So not quite supersonic, but that is to just get the goalie to move backwards. He probably assumed knocking back meant actually launching the goalie backwards.

That would hurt a lot I imagine

I suspect it would go over the threshold of what the goalie gear can withstand, and probably punch through?

 

[Brainiac]

Wouldn't work, he would be offside half the time.. And if he stands on the blueline, he's not gonna have enough leverage to influence the equilibrium..

.... man, it would change the dynamics of icing..

True, but you only need to get in the zone once to rapidly tilt the ice all the way down. From there, it's gonna be hard to get the puck out for the other team! Although it might be even harder for big Buff to get out of there if required...

Also, forget the 6'6 240 pounds goalie, you don't want that all the way back in your zone.

 

[PricePkPatch*]

True, but you only need to get in the zone once to rapidly tilt the ice all the way down. From there, it's gonna be hard to get the puck out for the other team! Although it might be even harder for big Buff to get out of there if required...

Also, forget the 6'6 240 pounds goalie, you don't want that all the way back in your zone.

Oh man... All of this is absolutely hilarious to consider. I know what I'll invest in when I'll win the Loto Max

 

[Stags209]

I suspect it would go over the threshold of what the goalie gear can withstand, and probably punch through?

Pressure= Force/Area, so lets say the front area of the puck is a rectangle 1" high and 3 inches across (if when the puck hits the chest protector half of it comes into contact).

P=(.165*7016.4)/(.0254m*.0762m)= 598.1 kPa!

Thats the equivalent of having water 61 meters deep on your chest acting on an area of contact with the puck. Ouch