# Spining formula

1. Oct 30, 2007

### phredbo

any one know the formula for an ice skater in an increasing spin

2. Oct 30, 2007

### jmnew51

Increasing rate of spin???

Jim

3. Oct 31, 2007

### rcgldr

It's complicated. Since the spinner does work by pulling a leg and arms inwards, the angular kinetic energy increases. You would need to know the angular inertia with leg and arms extended and then pulled in. Then you'd also need to know the amount of mass, the rate of spin, distance pulled inwards ..., to determine the work done (force times distance) while pulling the leg and arms inwards.

For a single point mass, if the radius is decreased by 1/2 the speed of the mass increases by 2, and the centripital force increases by 8.

4. Oct 31, 2007

### phredbo

hi jeff many thanks for the quick reply. all the best phres

5. Oct 31, 2007

### Shooting Star

The formula, or the idea, which the OP perhaps wanted is the conservation of angular momentum. The initial ang mom =I1w1=final ang mom=I2w2.

As Jeff has said, a lot parameters have to be known for the actual calculation. But, as you must have noticed, if you pull in your arms and/or a leg, then I decreases, resulting in an increase of w, which means you are spinning faster. And vice versa.

6. Oct 31, 2007