Ask the expert: The physics of the Winter Olympics

When Olympic athletes glide down a mountain or skate past their competitors, they’re relying on more than just talent. The laws of physics are ever present, controlling everything from nailing a jump and sliding a curling stone to flying above the halfpipe or beating a world record on the ski slopes.

Stuart Tessmer, a Michigan State University associate professor of physics, has always been fascinated by the connection between his two favorite topics — physics and sports. And in winter sports, he says, it’s all about friction.

Ice is covered with a thin layer of liquid water, reducing friction and making it slippery. The trick of many winter sports is to find just enough friction to control your movements, but not enough to slow you down.

Here, Tessmer explains the physics behind a few popular winter sports.

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Bobsled

The push

The object of bobsledding is to move the sled down an ice track as fast as possible. It all starts with a push.

Bobsled team members wear spiked shoes as they push the bobsled while running as fast and straight as they can. For these brief moments, the team wants maximum friction between their feet and the ice. As they push into the ice with their feet, the icy track pushes back at them, propelling them forward. That reflects Isaac Newton’s third law of physics — every action has an equal opposite reaction. The rails at the base of the sled slide along the water on the ice’s surface, reducing the friction between the steel and the track.

The jump

The team members must then jump into the sled without pushing it to the side. The added mass of the team members increases the pressure of the sled’s rails on the ice, accelerating melt and reducing friction along the track.

Once they’re in, they duck their heads down to minimize air resistance that would otherwise slow them down.

The course

Any movement from right to left could cause the sled to fishtail and lose speed. Every course correction increases friction between the sled’s blades and the ice. Staying in the center of the track is a team’s best chance at a winning run time.

Bobsled pilots take special care to memorize the course by heart. They need to know when a high-banked turn is ahead, when to expect a drop and when they can relax for a straightaway. They want just enough friction to maintain control and stay on the optimal path, but not so much friction that they lose speed.

Figure skating

The launch

A figure skater’s journey to seemingly defying gravity starts with friction between their skates and the ice. As the skater builds up speed, they leverage the third law of physics and push their blades almost sideways into the ice, propelling themselves forward. For spinning jumps, the skater needs angular momentum, a physics term describing a measure of energy in a spinning object. Angular momentum combines how fast an object is spinning and how mass is distributed around the center.

In an axel jump, the skater digs a toe of a skate down into the ice and pivots while pushing off, simultaneously swinging one knee out to the side and holding their arms out wide. Holding their mass away from the pivot point gives a greater moment of inertia, a measure of how difficult it is to rotate an object. It also gives the skater a greater angular momentum at the takeoff. These foundational physics concepts determine how fast the skater can spin before they ever leave the ice.

The spin

Once in the air, skaters maximize their angular momentum by immediately pulling their arms tightly into their bodies and twisting their outstretched knee over their other leg, decreasing the moment of inertia. Because angular momentum is conserved, the rate of rotation increases when the moment of inertia decreases. In other words, the smaller moment of inertia, the faster the spin.

The landing

To land with control, the skater extends their arms and one leg, increasing their moment of inertia. This slows down the rotation enough to land smoothly on one foot.

Hockey slap shot

The windup

The slap shot results from the collision between the hockey stick and the puck, but this seemingly simple move is far more complicated that it appears. It involves the transfer of stored energy and momentum from the blade of a hockey stick into the puck.

It all begins with the windup. The player wants to maximize the transfer of momentum (the speed of an object) from the blade to the rubber disk. First, the player raises the hockey stick and twists their hips. They then unwind by swinging the stick and shifting their weight forward to generate as much blade-speed as they can.

The bend

Surprisingly, the player purposely slaps the blade of the hockey stick against the ice before it ever hits the puck. Though it might not look flexible, the shaft of the hockey stick bends back as a result, storing potential energy in the hockey stick.

The collision

Finally, the potential energy is released as the hockey stick snaps forward with even greater speed, whipping like a slingshot and transferring incredible momentum to the puck. This momentum rockets the puck into the air and hurtles it toward the goal net.

Physics is the unsung hero of the Winter Olympics. Understanding its principles can give you a new appreciation for the feats accomplished by world-class athletes from around the globe. Enjoy the games but also raise a glass to Newton’s laws of physics governing each move.