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The Science Of Sledding: How Friction & Wind Resistance Affect A Sled's Speed

Because of friction, sleds don't technically touch the snow and instead ride on a small layer of water created by the heat of the sled sliding down the hill.

Story first aired on Feb. 2, 2021

Sledding is one of many ways Wisconsinites pass the long and snow-filled winter. But when it comes to sledding, there is actually a lot of science that goes into getting from the top of the hill to the bottom.

Jax Sanders is an assistant professor in the Physics Department at Marquette University. Sanders says that sledding showcases two important concepts in physics — air resistance and friction.

Air resistance is the fact that despite not being able to see the air around us, there is something taking up that space and to move through it, energy has to be used. A general rule of thumb Sanders explains is that the larger and wider an object is, the more energy is needed to move through the air.

When it comes to sledding, Sanders says it's important that you make your body flat and pointy to have the least amount of air resistance while you sled down a hill.

“You want to make your body as pointy as possible with the smallest cross-sectional area to the direction of travel,” Sanders explains. “So if you want to go faster, lean back in your sled.”

The other concept is friction — when objects rub against each other, they create heat. This is why when your hands are cold, you can rub them together to warm up.

In sledding, the main point of friction is between the sled and the ground. Despite the fact that it may feel like you’re sledding on the snow, technically the sled isn’t touching the snow.

“What actually happens is when you are sliding on the snow, having that little bit of heat, just remember you rubbing your hands together, friction causes heat, you’re melting the top layer of snow into water. So if you are melting the top layer of snow into water, you’re making this little bed of water to float on,” says Sanders.

But not all snow is created equal when it comes to sledding.

“Extremely fresh snow is actually going to have a higher coefficient of friction, it will exert a higher frictional force than snow that has been sitting for a little while, so very fresh snow is not going to be as fast,” says Sanders.

The temperature of the snow is also an important factor in how fast a sled will get down a hill.

“You want to be on snow that is in that nice 14 to 32 Fahrenheit sweet spot, which is coincidently a great temperature to be outside in the winter,” notes Sanders.

Sanders explains that there is room for experimentation when it comes to sledding because each hill and each sled is going to have different variables that affect just how fast a sled can get down the hill. So next time you hit the hills to go sledding, remember you are doing it for science!  

Audrey is a WUWM host and producer for Lake Effect.
From 2020 to 2021, Jack was WUWM's digital intern and then digital producer.