minipost
In figure skating you to convert some of the kinetic energy from your speed across the ice into air time during which you spin. You launch yourself skyward using the teeth on front of your blade like the base of a lever (way more inefficient than pole vaulting). Once it leaves the ice your center of mass follows a simple mostly parabolic trajectory defined by gravity. You can't change that path, but you have another trick up your sleeves.
To start a spin you need to generate a lot of torque. This is done by generating large forces in opposite directions against the ice. (read powerful leg muscles!) Now the trick. Physics has several conservation laws. We'll make use of conservation of angular momentum. It's the product of the rate of spin and the moment of inertia. The moment of inertia is basically a measure of how mass is distributed around an axis of rotation. The further out the mass from the axis of rotation, the higher the moment of inertia. You can't change your mass, but pull your arms in and your moment of inertia decreases and your rate of spin increases in response.
I watched about a dozen world class skaters carefully frame by frame doing the same quadruple jump. The longest flight time I saw was 0.66 seconds - most of the others between 0.63 and 0.65 seconds. They were spinning a bit over nine times a second during the core part of the flight, but much slower just after takeoff and before landing.
The 0.66 seconds of airtime resulted from increasing the height of his center of mass by about 53 centimeters. It is difficult estimating the force of his impact when he hit the ice, but it was probably about eight or nine times his body weight -- all on one skate.
Clearly there's a lot of skill and training. Training informed by kinesiology - a mix of anatomy, physics and sport,. It's interesting to think what body type is favored and what someone who could easily land quintuple jumps would be like physically.
The physics requirements demand a light and very thin body to optimize range of control over his moment of inertia. Very powerful legs to get the highest possible speed and liftoff for maximum flight time as well as generating an enormous amount of torque against the ice. The arms must be strong enough to move in quickly and there is some advantage having longer arms.. eg.. the skater's wingspan is likely to be longer than his height. I would be surprised if his height is much more than 170 centimeters and his mass greater than about 60 kilograms.
One might dream of what could be done give more air time. Perhaps an event on the Moon with a sixth the gravity and flight times approaching four seconds.
But wait - there's a sport for that. Freestyle skiing. Similar physics in that you're playing with your moment of inertia, now concentrating on all three axes rather than one, as your body moves through it's Newtonian parabola.
Comments