The physics of ski jumping

Hello again, we are in a winter wonderland, and I love it. As long as it is winter it might as well snow a little bit. I was going to continue my discussion on peat bogs this week, but my peat guy in Cromwell had to cancel our interview. No problem, so many things to wonder about.

Yesterday I went cross-country skiing with two of my grandkids, ages 5 and 8. Halfway through our ski, I built a little ski jump off to the side and watched as they soared 12 feet through the air and landed on their backs in the fluffy snow. It reminded me of the first time I went off a real jump, in Pine Valley last year. I was 65. I am now 66; I survived.

I had coached high school cross-country skiers since 1979; last year was my last season and I have wanted to go off a real ski jump for a long time. Pine Valley is the home of a vibrant jumping community, with real jumps and a jumping club that numbers 40 kids, ages 4 to 18.

Sure enough, on one of the last days of the season, the perfect storm hit. Cross-country practice had ended, the lights were on the jumps, jumpers were showing up for a night of jumping, and adults who knew what they were doing were there (Jon Waugh, Pat Marciniak, Ken Ripp). It was on. I was too chubby to put on a jumping suit, but Jon Waugh found me a pair of skis that were 9 feet long and weighed nearly 20 pounds. Thankfully, he also found a crash helmet for my noggin.

After four practice jumps on the smaller 10-meter jump, I was ready for the 20-meter. I put my skis over my shoulder and climbed the steps to the top. My coach, Aidan Ripp, gave me some last-minute instructions at the top, and the last thing I heard him say as I sped down the ramp was, “Oh, my God!”

As I was flying through the air, I got to wondering about the physics of ski jumping (more about that later). Anyway, everything was great until I landed. I landed on my face, and saw my left ski flying off to the left, my right ski and boot flying off to the right, and blood flowing down the middle of my face.

Now, what about the physics of ski jumping? It is all about going fast down the ramp, jumping at the end while maintaining forward inertia, and staying in the air as long as possible.

I have included a drawing of the forces involved in this amazing sport. Gravity will help you gain speed on the ramp, friction on the snow will try to slow your skis down, and air resistance will try to slow your body down. When you actually jump, the force of your muscles will lift you off the ramp. While in the air, you will use air pressure to stay aloft while still trying to slice through that air in a forward direction.

I have talked to jumpers about how they use and resist these ski jumping forces.

Gravity will always pull you down the ramp, your mass and your speed will give you inertia as you leave it. The correct wax and ski will lessen snow friction and a good tuck will lesson air resistance; both of these lead to the highest possible speed down the ramp.

When you leave the ramp, the force of your quadriceps, glutes, and calves will lift you a bit, and the position of your body will help you glide through the air like a flying squirrel, hanging aloft as long as you can before landing.

In the photo you can see the jumper is trying to catch air with his arms, hands, torso, and skis spread in the V position. The final force affecting you will be the resistance of the ground as it stops your descent.

I wonder what it would be like to ski jump on Mars, where less gravity would allow you to lift higher and fall with a little less acceleration; less gravity would also slow your speed down the in-run, mmmm?

FDLTCC science tutor Glen Sorenson was Minnesota Teacher of the Year before he retired from teaching science at Proctor High School after 30-plus years. He is an avid outdoorsman who most recently coached the Lumberjacks Nordic ski team.