Figure skating is one of the most popular sports in the winter Olympics. In this exclusive Scientific American video, contributing editor Christie Nicholson takes you inside the sport, to explore the physics behind a figure skater’s spectacular moves. Along the way, she discovers her inner Kristi Yamaguchi.
Presented by Christie Nicholson
Filmed and edited by Eric R. Olson
Have you ever wondered how these Olympic figure skaters float so fluidly over the ice or spin so fast through the air?
Well, Olympic figure skaters endure years of physical training but there’s something else that’s crucial for their success and that’s the law of physics. And like all physical systems a figure skater’s body depends on three things and that’s energy, motion and mass.
But first of all, let’s take a look at ice. We wouldn’t have ice skating at all if it wasn’t for a very unusual property that makes ice slippery. For instance, if we tried to skate over another type of solid like glass, we’d quickly learn why glass skating never caught on. There’s simply too much friction between the metal of the skate’s blade and the surface of the glass.
But ice is different. Even at temperatures well below freezing, its great for skating. And that’s because water molecules on the surface of solid ice form very loose chains, as opposed to water molecules in an ice crystal at the center. And what these loose chains form is a frictionless, almost liquid-like surface.
But even on a nearly frictionless surface like ice, it takes a force–Newton’s second law–to get a skater’s mass moving. And in the human body that force starts out as something we can’t see, as potential energy trapped in muscle cells. And these cells contain something called ATP, a kind of molecular spring that stores the energy from food.
When a nerve impulse from the skater’s brain signals her leg muscles into action, millions of ATP molecules pass their energy onto protein fibers in her legs. And these fibers act in concert to extend her leg, pushing against the ice and turning potential chemical energy into kinetic energy–the energy of motion.
So to move forward on the ice what you do is dig your blade in and you push back like this to move forward. But if I wanted to move up, as in a jump, what I do is I push down, the ice generates an upward force and its that force that propels me in the air.
But what happens when a skater starts spinning and then get’s faster and faster and faster, long after she has pushed off the ice. Well here its physics again and the idea is that momentum must always be conserved.
It works like this. As a skater spins she is carried along by a rotational momentum and this momentum depends on two factors–how far the skater extends out from her own central axis and her speed of rotation. Once she is spinning the only factor the skater can control is the distance from her own center, so she pulls her limbs inward, and because her momentum must be conserved the spin gets proportionally faster.
The same principle applies to spinning jumps, the skater starts with her arms outstretched and pulls them in tighter to get the most spins in the air. Of course, you need a lot more than physics to be a good skater and from the looks of me, I need a lot more practice.
For Scientific American, I’m Christie Nicholson waiting to get back on the ice.
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Terriffc. Lots of fun and great explanation of the physics.
With a little more training, Christie can be in the Olympics in 4 years.
Link to thisChristie Nicholson makes one misstep in this otherwise interesting piece. A skilled skater does not push back to go forward. Rather, except in very specific and exceptional situations, the skater’s pushing leg moves out to thee side, pushing off the inner edge of the pushing blade. One can see this motion in its extremest form in speed skating, but it is true in all skilled skating, both forward and back. The push appears to be from the back because the skater is moving forward. Nicholson does not mention to crucial importance of the blade’s edge in every stroke and its interaction with the shifts in the skater’s weight that control the skaters movements. The great skaters one sees at the Olympics are masters at controlling edges and exploiting weight shifts and posture, and the rest of us spend countless hours trying to learn these difficult and highly counterintuitive skills. Doing so at a high level takes an extremely high level of physical fitness. Nicholson is an enthusiastic but, it appears, not a highly trained skater, and an understanding of edges and their importance takes a long time and highly competent instruction. Still, except for that point, this an informative and enjoyable piece.
Link to thisReporting while skating on ice…. i love it! What other hidden talents do you have, Mrs. Nicholson? Let’s see you land that triple jump.
Link to thisShe got the explanation about the friction on ice wrong. Ice (or water) is a very unusual substance in that it expands upon freezing. Very few other substances do this. So when ice is subjected to pressure (blade of the skate), it wants to change back into a liquid, thus providing the lubrication needed to reduce friction.
This is also why ice floats. Because of the expansion, it is less dense than water. Good thing, too, because otherwise all our skating rinks would have to freeze from the bottom up. And frozen lakes would probably never thaw.
And by the way, if it is cold enough, (like Pluto, say), you couldn’t ice skate because you couldn’t generate enough pressure to change it back into liquid water.
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