Beware of Flying Pucks

Brandon Kaput, Jerry Vergona, Lance Cruz, Elias Bassil

We want to measure the spin of a hockey wrist shot the pucks overall velocity.

Hockey Puck
Hockey Tape
Hockey Stick
High speed Camera
Hockey Gloves

Firstly, the pucks will be marked with white tape. Once we have that done, the shooter will make a wrist shot from a shooting board (which mimics the friction of ice, so doing this experiment on ice would be ok too). Another person will be manning the camera, and another just spectating. Those two will be set behind or off to the side of the shooter, watching, recording, and analyzing the shot, watching for the revolutional velocity and the puck's overall velocity.

Introduction to the Wrist Shot

    The wrist shot is one of the most important shots in the hockey player's arsenal. The wrist shot is executed by sliding the puck to the middle of the blade of the stick. The puck is then pushed along the ice, while simultaneously sliding the puck to the tip of the blade. As it slides down, the puck begins to spin. The puck spin uses the same idea as the football spin, causing increased accuracy. This is because the puck will have a constant air resistance, making it easier to follow its intended path. The puck will generally go in the direction of the follow through, making it a very reliable shot in tight situations. Ovechkin, Hossa, and Franzen are all known for their extremely accurate wrist shots.
    By understanding the physical mechanics of the wrist shot, such as the amount of spins in the length of time of the shot, the better the results will be. 


All the data that we present is based on this sole video, known as Shot3:

As said in the introduction, the rotations, or revolutions, of the puck help the puck travel straight and true. This is because the uniform movement of air caused by the puck's spin, which stops any unnecessary movement. From the video Shot3, we saw that one full rotation occurred in 30 frames (frame 105-135).

There are 500 frame per second, so:

1rev        x     500 frames   = 500/30= 16.6 revolutions per second (RPS)
30 frames           1 sec


Velocity is the change in position over time. In a sport like hockey, the speed of the puck is key. The faster the shot, the harder it will be for the goalie to stop it. So generally, as long as the shot is on target, you want it to be as fast as possible.
Unfortunately, the video we took didn't play nice with Tracker. After we tracked the puck through its motion, we set the graph to give us the velocity, which then gave us  this:

The velocity is supposed to give us a straight (albeit diagonally oriented) line, which we obviously did not get. After speaking with Mr. Dickie, he showed us that we had not changed the time to be scale with the frame count. After he fixed this for us, he also showed us how to use the linear fit to get the velocity from the slope.
So, instead we measured the amount of frames it took the puck to travel one meter, using dimensional analysis to convert it to a usable number. We got this from analyzing the numbers from the video when we put it in Tracker, so here's the math (and a video explanation):

1 Meter       x    500 Frames   x   100 cm    x   1 inch   x    1 mile      x      360 sec     = 62 mph
7 Frames           1 second           1 meter       2.54cm     63360 inch           hour

Tracker showed us that the velocity was 25 m/s. Using calculations we got a velocity of 27m/s (62 mph) , which is very close. It was feasible data, considering the average velocity of a wrist shot for a teenager is 50 mph.

Acceleration is the change in velocity over time. Again, we could not use Tracker's built in feature to calculate the acceleration of the puck either because the graph that came out was also messy. We used the data we had gathered prior to this step in a formula to solve for acceleration instead. These are the calculations for the acceleration of the hockey puck, starting the moment it leaves the hockey stick.

v=ma; v is velocity, m is mass in kilograms , a is acceleration
v=62mph= 27m/s

27m/s   = 119 m/s2

The mass of the puck is 8 oz or 0.22676 kg.

Impact force is the shock applied to an object by another object. In this instance, the hockey stick is imparting impact force on the puck. The puck is in contact with the stick for 18 frames.

f=  27-0
f=   500(27)      =   750N

We found the momentum of the puck also. The calculations for the momentum are tacked on to the last 20 or so seconds of the "Forces" video.
P=momentum, m=mass, v= velocity

P= 0.2267(27)
P= 6.1209 m-kg/s

Work is defined as the transfer of energy from one object to another. In this project, the work is done by the hockey stick blade on to the puck.
W = Fd
W = Work, F = Force, d = Distance
W = 750 x 1.2m
W = 900J

Interactive Physics:
This two part video of interactive physics, displays a close enough simulation of a wrist shot. The first part of the video shows what happens to the puck after it is hit by the stick, while the second part if you focus in closely shows that the average velocity of the puck denoted in the video as "circle 9" is approximately 27m/s. The results are acceptable because they are close to ours, since in the simulation we projected the stick with a force of 754 N towards the puck. Now obviously the stick does not spin around after a wrist shot but we are not experts in using the program and we apologize for the low quality video our phones are cheap.   


    The experiment was alright. Why do I just say "alright"? Well, for one thing, Tracker needs some more spit and polish. The program itself is good, but the windows that you often try to access don't appear correctly, gimping the entire process severely. Also, we had a hard time getting Tracker to emulate what was shown in the example videos, such as the velocity and acceleration graph problems. Despite this we tried to do our best with what we had and got some results. We were able to get the rotations per second, the speed, the momentum, and other things. The speed of the puck was in reasonable range at 62mph, because according to Jerry his highest mph shot was high 70s. Another is that we couldn't get quite as much information as some other groups, which may or may not be due to program literacy.

    If we were to do this again, I think it would be best to compare two types of shots, to see the differences in velocity, acceleration, and spin. Having another type of shot would make it much easier to delve into the power of the spin, because we could then compare the fundamentally different calibers of spin speed of the shots. We could then gauge the effect of spin on the shots, as well as their velocity, acceleration, and accuracy.