ôô

# The Fascinating Physics of Figure Skating

Let’s break down some of the crucial elements behind figure skating's moves like the loop, flip, salchow, axel, and lutz.

By
Sabrina Stierwalt, PhD
Episode #273
The Quick And Dirty
• A skater’s vertical velocity (speed upward into a jump) helps determine how high they can go.
• The angular momentum of a skater is the product of their linear momentum and their angular velocity or their rotational speed. Angular momentum means that spinning things like to keep spinning until acted on by an outside force.
• The vertical velocity, angular momentum, and speed all contribute to the ultimate goal for a figure skater—hang time to complete their spins.
• Skaters also rely on friction, a force that causes energy to dissipate, to start and stop their movements across the ice.

Figure skaters not only have to perform incredible feats of human strength and agility, but they also have to push the limits of what is humanly possible while making their movements look easy. Their motions appear graceful and smooth as they hurtle their bodies through the air with nothing but the hard ice below.

As spectators, we take for granted that a figure skating routine will involve multiple jumps which incorporate triple and even quadruple spins in a single jump. Executing the perfect jump requires a precise combination of speed, force, vertical velocity, angular momentum, friction, and of course timing. Let’s break down some of these crucial pieces that go into the perfect loop, flip, salchow, axel, or lutz.

## Vertical Velocity

A skater’s vertical velocity, or their speed upward into a jump, helps determine how high they can go. Their altitude in turn determines how much time they have in the air before they return back to the ground and thus how much time they have to execute a spin or spins. A skater achieves vertical velocity by extending their leg downward to push down on the ice. The ice in turn pushes back providing a force upward.

A skater’s vertical velocity, or their speed upward into a jump, helps determine how high they can go.

The vertical velocity needed to reach a certain height is the same for any skater but the force needed to reach that velocity depends on the size and weight of the skater as well as how long the force is applied to propel the skater upward. Stronger muscles are required to create stronger forces. Skaters typically launch themselves off the ice skaters around 10 miles per hour and reach heights anywhere between one and four feet.

## Angular Momentum

Another fundamental physics principle on display in a figure skating jump is the law of conservation of angular momentum. The angular momentum of a skater is the product of their linear momentum and their angular velocity or their rotational speed. Angular momentum works similarly to linear momentum in that spinning (or moving) things like to keep spinning (or moving) until acted on by an outside force. In other words, a larger angular momentum allows a skater to spin faster in the air until she hits the ground.

A larger angular momentum allows a skater to spin faster in the air until she hits the ground.

You may have noticed that skaters tend to begin their jumps with their arms extended but while in the air they draw their arms in toward their body to minimize their size as much as possible. This is because angular momentum must always be conserved without that action from an outside force. If you have a spinning chair, you can try this for yourself at home. Pulling your arms in reduces your rotational inertia so your angular velocity must increase in order to balance out this reduction and ultimately conserve angular momentum. And just like the figure skaters, you can slow yourself down by extending your arms outward again.

## Speed

The vertical velocity, angular momentum, and speed all contribute to the ultimate goal for a figure skater which is more time in the air—called hang time—to complete their spins. The laws of physics help us translate a skater’s jump height to time spent in the air. At four feet, skaters have a full second of hang time, but more typical jump heights of one to two feet leave only 0.5 and 0.7 seconds to perform their spins. For comparison, snowboarders and skiers tend to see hang times of as long as three seconds giving them much more time to work with.

The vertical velocity, angular momentum, and speed all contribute to the ultimate goal for a figure skater which is more time in the air—called hang time—to complete their spins.

To pull off a jump that involves a quadruple spin, a skater will need to maintain an average rotational speed of around 340 revolutions per minute (depending, of course, on the hang time). Skaters are known to reach peak or maximum speeds, however, of up to 440 revolutions per minute. Speeds approaching 500 revolutions per minute would be required to execute a quintuple jump which has led experts to question whether a quintuple jump is even humanly possible.

## Equipment

Although strength, talent, and athleticism are essential ingredients for a successful figure skating jump, having the right equipment also helps. The leather skates worn by figure skaters are stiffer than those worn by hockey players or speed skaters in order to provide more ankle support. This trade off in flexibility for support is necessary due to the repeated hard landings onto the unforgiving ice.

Researchers at Brigham Young University attached sensors to the bottoms of skates to see just how intense those landings are. They found the impact to be five to eight times the skater’s body weight. Now imagine taking that hit 50 times or more a day!

## Friction

Skaters also rely on friction, a force that causes energy to dissipate, to start and stop their movements across the ice. To best harness the power of friction, a figure skater actually has two blades: one inner blade and one outer blade with a groove in the center. These blades are cut at an angle to help skaters steer themselves around tight corners and to provide extra grip against the ice. This additional grip translates into a stronger force from the skater downward onto the ice which is then countered by a stronger force upward from the ice onto the skater and thus an additional push into each jump.

Skaters also rely on friction, a force that causes energy to dissipate, to start and stop their movements across the ice.

The blades also have toe picks, or pointed teeth at the front, to dig into the ice when they want enough friction to come to a stop or to help launch into a jump. In contrast, speed skater’s skates tend to have longer, wider blades with the goal of generating more heat as they move along the ice. This heat will cause the ice to melt a little and this melt water is great for gliding during speed skating but not so great when you have to make quick changes in your movements as in figure skating.

The Winter Olympics and other ice skating competitions will also employ a large number of ice technicians to keep the ice smooth and, well, icy. The ice is made from water treated with both reverse osmosis and deionization techniques in order to remove contaminants like fluoride found in regular tap water that tend to pool together and thus can cause ripples when the water is frozen.

Since figure skaters are in constant motion, small divots in the ice are okay and will not throw a skater off balance. In sports like curling, however, even the slightest imperfection can affect the results of the competition, so continuous patching of the ice is required. Although it doesn’t affect performance, for most sports, the ice is also painted in order to make it sparkle.

Please note that archive episodes of this podcast may include references to Ask Science. Rights of Albert Einstein are used with permission of The Hebrew University of Jerusalem. Represented exclusively by Greenlight.