If you missed the incredible performance of the French Brian Joubert on the ice in Vancouver, here is an assignment to catch up.

Have you ever noticed that knowing skate skater plays with his arms when he turns on itself in the air or on the ice. These effects do not handle an artistic purpose. The skater in fact applies a physical principle that allows him to an arm movement, greatly increase its speed and possibly its rating, if not break the figure afterwards.

To become a human spinning top secret skater is not only the action of his skates. You can see in the video above, as Philippe - aka D'Artagnan - Brian bring their arms over their chests at the beginning of their rotation. And apart again to stop their movement.

By changing the position of his arms skater changes that inertia is known, . Reduce the moment of inertia of the skater decreases more the speed increases.

The skater's weight is distributed around its axis of rotation extending from head to foot. As the animal is articulated, the mass is distributed at distances greater or smaller that axis.

Arms outstretched, the mass of the arm is farther from the axis of rotation, thereby increasing the moment of inertia. When the skater's back on his chest the moment of inertia decreases. The variations of the moment of inertia are particularly important in this case that it depends on the square of the distance between the ground and the axis of rotation.

Take the test with a broom. It is much easier to do quickly turn along the vertical axis (the handle to the brush) rather than along the axis passing through the middle of the handle - way monk shaoling. In the first case, the mass of the blade is much closer to the axis than in the second, and therefore the moment of inertia less.

For those who want to get their hands dirty mechanics, here is the explanation less succinct. In the case of our skater, there is conservation of angular momentum. The latter is equal to the product of the rotational speed by the moment of inertia. When the moment of inertia decreases, the rotational speed increases. To the delight of D'Artagnan.

For fans, the next time you go to the rink, keep your arms close to you to run faster on your own.

About Jonathan Parienté