## Saturday, October 24, 2015

### The Physics of Curling

As a captain of the curling team, I am always looking for ways to improve our game; thankfully, I think what we’ve learned in Physics 111 this year will help us defend our national ranking.
The other think to consider is when we’re trying to throw take out shots. Below is a video of some really impressive take out shots:

In my opinion, the take out shots are the most fun to throw, but getting enough velocity on the stone can be difficult.  In relating initial and final velocities of each stone, we can assume that the stones experience a perfectly elastic head-on collision (they make a noise when they collide, so energy is not technically conserved), ignoring the static friction between the stone and the ice.
When curling, the stone that is hit (1) has an initial velocity of 0 m/s, and the stone doing the hitting (2) has a final velocity of 0 m/s. With this, we can see:
which means that the stone that is hit leaves the collision with the same velocity as it was hit with (in reality, slightly less) in the same direction of motion as the hitting stone. Because the stones are moving around 2 m/s at this point, the house (scoring region on the ice) has 3.5m radius, and velocity is proportional to distance traveled, this time not ignoring friction, a change in 1 m/s in either direction can mean the difference between hitting the stone out of the house, or having it stick around. This difference in distance traveled can mean the difference between scoring in the end, or losing the end, which will have major ramifications in point totals for the game, and throwing order for the following end.
Another aspect of curling that physics can explain is the importance of sweeping stones. When a stone is thrown, if it does not have the correct initial velocity for the type of shot you are trying to make, sweeping the stone can make the stone travel farther. How can this be so? Conservation of energy:

If we are trying to see what makes the stone go further without having changed the initial velocity, then the only variable that can logically be changing is μ. Sweeping melts the pebbles on the ice, thus lowering the coefficient of friction, which is what makes the stone go farther when it is swept. Another interesting and less understood part of sweeping, is that it makes the stone curl less; this might be better understood if we look at why a stone curls at all.
Although there is a lot of curling that Physics 111 can explain to us, there is one thing that is still not understood about curling: why it is that the stone curls in the direction of motion? If you were to push a spinning cup on a flat table, the cup would ultimately curl in the opposite direction of the cup’s spin. So  why doesn’t the curling stone do the same thing? The answer is in the pebbling of the ice. This video does a good job of exploring why it might be so:

The short answer: we don’t really know why it is, but hopefully, as we move into rotational motion, we’ll be able to understand better the physics of curling.