MadSci Network: Physics

Re: What types of physics are in fiqure skating, and how do they work?

Date: Sat Feb 14 19:09:42 1998
Posted By: Tom Cull, Research Associate, Washington U Med. School
Area of science: Physics
ID: 887219551.Ph

Figure skating is a great example of physics in sports.  Usually one can do 
pretty good by considering conservation of energy and conservation of 
momentum (angular and linear). 

Two important conservation equations are:

angular momentum = (momentum of interia) X (rate of spin).
linear momentum = (mass) X (velocity).

Momentum of inertia is basically a measure of the distribution of mass from 
the axis of rotation.  Bigger mass or mass spread from the axis means 
bigger momentum of inertia.

Let's just consider two figure skating events: jumping and spinning. 
How do skaters start spinning?  Well the most basic mechanism to create 
spin is to generate a torque with the feet by exerting equal and opposite 
forces with the two feet against the ground with some distance between the 
lines of action of the forces, or more common in ice skating by twisting 
with one foot against the ground (ice). 

The skater can achieve a great rate of spin by storing angular momentum in 
arms and the push leg and then pulling those limbs in close to the body.  
This maneuver uses torque to generate angular momentum and then pulling the 
limbs close to the body reduces the moment of inertia.  The rate of spin 
goes up to conserve angular momentum.

Jumping in figure skating can be aided by changing linear momentum into 
vertical momentum in a manner similar to pole vaulting.  The skater builds 
up a great speed (which means big linear momentum) then the toe of a skate 
is pitched into the ice and the leg is used sort of like a pole in pole 
vaulting.  Up to a point, the faster a skater moves going into a jump the 
higher and farther he/she will be able to leap.

Angular momentum can be carried into the jump by applying a torque just 
like when spinning and when the legs and arms are drawn into the body the 
skater spins in the air.  To land with a smaller rate of spin the skater 
opens up his/her arms and the non-landing leg.  A bad landing happens when 
the skater fails to control the angular momentum upon landing.  If you 
notice almost all jumps result in landings that then proceed in a curved 
arc allowing the skater to gradually control some of the angular momentum 
gained in the leap.

Olympic skaters practice and practice to learn how to control momentum.
Back in the 1980's triple jumps were considered the cutting edge of the 
sport.  Now triple axels, triple toe loops, triple lutzes, and triple 
salchows are common.  In fact triple jump - double jump combinations are a 
required element.  Many skaters do triple jump - triple jump 
combinations as their best move.  Some of the most athletic skaters can 
even perform quadruple axels in practice with little effort.  Soon I 
suspect quadrupole axels will be common in competition.  US skater Michael 
Weiss has landed a quadruple lutz in previous competitions and was a 
quarter revolution short on the jump in his Olympic performance.  And a 
young Chinese skater was the first man to perform a quadruple jump-quadruple 
jump combination.
To find out more about the different types of jump try the official 1998 Winter Olympics Site:
Follow the tabs to figure skating.

I hope these examples help you think about some other aspects of the 
physics of figure skating or even the physics of other sports.


Tom "I Cannot Skate" Cull

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