Sledding and Physics

It’s almost time to take the toboggan down from the garage rafters. My son is like Calvin. Any snow is enough snow. I hope for enough snow to cover the bracken on our favorite hillside. Any less than full cover makes for a rough ride. If we’re lucky, we’ll get a big fall of powder. It’s fun to fly down the hill throwing powder over the front of the toboggan and then walking away like snowmen. Powder isn’t as fast as packed snow, but it isn’t as hard either. I bought a 92” toboggan years ago, one long enough to seat the five of us, at least when the kids were small. The first year tobogganing, I felt every knob on the hill and the moguls stunned me. I don’t remember being sore as a kid. The next year I bought a pad.

This year I’m going to wax the toboggan and see if we pick up speed. Andrew Posma’s website at the University of Alaska Fairbanks rates waxed wood’s coefficient of kinetic friction second only to sleds with metal runners. Less friction translates into greater speed. Interestingly, plastic sleds have the highest coefficient making them the slowest sleds. As a boy, I rode my father’s Flexible Flyer after finding it in my grandfather’s barn. It was especially fast in packed snow and ice. On powder, it was slower than the approach of Christmas break.

The last time I sat astride Dad’s Flexible Flyer I turned sideways on a steep icy hill and flipped, which raises questions of helmet use. I’ve seen websites that recommend wearing helmets for sledding. I understand that being the only kid on a hill with a helmet is like wearing a sandwich board with DWEEB on it. As an adult, I don’t think I care what my sandwich board says. Your head is where you reside so it’s worth protecting. After my spill, I rode on my belly to increase my stability. Head first, of course, like a battering ram. I never thought of stuff lie this until I had kids. The American Academy of Orthopaedic Surgeons includes guidelines for safe sledding in its position statement on winter sports. Because a toboggans cannot be easily steered, it recommends not using them. On the other hand, an article in Slate, “Hardheaded: Why My Son Will Not Be Wearing A Sledding Helmet” examines arguments for and against wearing helmets and concludes that choosing a proper sledding site, one free of trees, poles, and other obstructions which account for most sledding injuries, makes more sense. I agree.

The first day we used our new toboggan the only hill within walking distance was a cemetery. Toboggans are like muscle cars. They go fast in a straight line but are bad in turns. Much of our excitement came from whizzing past headstones. We missed them all. I’ve learned to forgive myself. I was younger then. The next time out, I strapped the toboggan on the roof of the car, and we discovered our fast and unobstructed hill.

Some schools permit sledding at recess. The schools my kids attended did. Students were required to wear snowsuits, boots, gloves, hats, all the stuff a reasonable adult would assume but many kids never consider. Helmet use was never required or advised. The hills were never very steep and always unobstructed. If your school is in an area that gets snow and permits sledding at recess, sledding is a good opportunity to investigate aspect of physics: energy, inertia, friction, acceleration. Its also a good way to burn off some the steam that builds up during winter.

For an overview of sledding and physics, see Dr. Chris Stockdale’s short (4:25) video discussion The Science of Sledding.

Students in grades 4-8 will find Posma’s UAF site a primer on the forces involved in sledding. Note: this is a university student project and has a few typos, but the information is good and specifically applied to sledding.

Newton’s Second Law of Motion explains why we come to a stop and the end of a ride. Students in grades 9-12 will find the complete discussion of Newton’s Second Law useful. This website includes teacher guides.

Students in all grades can practice science while sledding with the worksheet The Physics of Sledding.

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