Modern skates are marvels of science. They’re made with lightweight materials that keep moisture out, they feature customizable tongues for varying levels of stiffness, and they’re outfitted with blades that help increase your speed.
Knowing this, you might find it hard to believe that the first pair of skates, used in Finland more than 3,000 years ago, consisted of sharpened animal bones attached to boots with leather straps. The action was more gliding than skating, since the bone blades slid on top of the ice rather than cutting into it. In the 13th century, the Dutch invented skating as we know it by designing skates with sharpened steel blades. For the most part, modern skates have retained this design.
The physics of ice
At the very heart of skating is, of course, ice. The action of skating may seem simple, but there’s a complicated science behind it, one that physicists are still trying to understand—especially when it comes to the question of why ice is slippery.
The main theory explaining why ice is slippery, allowing skates to glide along its surface, is more than a century old, but physicists have recently started to refute it. Known as “pressure melting,” the traditional theory states that the pressure from the skate lowers the melting temperature of the top layer of ice, causing the ice to melt. The blade then glides on the thin layer of water, which refreezes as soon as the blade passes.
A similar theory suggests that friction is the reason ice is slippery. The rubbing of the skate blade over the ice heats and melts it, creating a slippery layer. However, neither of these theories explains why ice is still slippery at temperatures lower than -3.5° Celsius, when more pressure than the weight of the average skater would be required to melt it.
Yet another theory suggests that ice is inherently slippery. It argues that water molecules at the ice’s surface vibrate more because there are no other molecules above them to keep them in place. The top layer of ice therefore stays unfrozen and slippery, even at temperatures much below freezing.
The mechanics of skating
For those who are just learning to skate, the idea of charging across a rink and then stopping on a dime, spinning like a corkscrew, or swirling around backwards can seem absolutely terrifying. Hockey players and figure skaters have mastered the physics of skating in order to spin, jump, and rush across the ice. But for beginners, the most important concept is the science behind accelerating and decelerating.
When skating either forwards or backwards, the skater digs their blades into the ice and pushes off from the surface. The friction between the blade and ice is lessened because the ice is so slippery and smooth. To accelerate, skaters lean forward so they exert a strong force on the lower part of their bodies, which gives them more momentum. For decelerating or stopping, skaters must exert more pressure into the ice while turning their blade slightly inwards or outwards to increase the friction against the ice.
The mechanics of skating relate to Isaac Newton’s first law of motion—an object in motion tends to stay in motion unless acted on by a force. So unless skaters create enough friction, they’ll tend to keep gliding. Newton’s theory also explains why you see so many beginner skaters slamming into the boards. Until they learn how to stop by turning their blades and increasing the friction, it’s the only way they can stop.
Why sharper is better
Sharp skates are better for picking up speed, making sharp turns, and stopping quickly. This is because the blades cut deeper into the ice, allowing for more resistance to the momentum when planted. They also allow you to skate faster because of the reduced friction: A sharper blade has less surface area, and therefore glides farther on the ice due to less friction acting against its motion.
Understanding the physics of ice might not make you the next Sydney Crosby when you strap on your skates, but it should satisfy your curiosity the next time you’re gliding across a placid lake on a crisp winter day.