The force that helps propel ice skaters in their spins is centripetal force or acceleration. Centrifugal and centripetal force are often confused, particularly when it comes to circular momentum. Though commonly used to describe spinning outward, centrifugal force does not actually exist. Objects traveling in a circle are actually moving inward, though inertia does resist centripetal force's constant change of direction. Skaters demonstrate centripetal force in a variety of spins, during pairs and individual competitions.
Centripetal Force
Centripetal force is the tendency for objects to move toward the center of a circle. The word centripetal actually means "center seeking." Objects moving in a circle are constantly accelerating because they are also changing direction consistently to maintain their course. Acceleration is not just speed, but rather velocity, which is speed plus direction. The acceleration of an object in centripetal motion is always toward the center of the circle.
The Death Spiral
Ice skating provides ample opportunity to test variations of centripetal force. During pairs skating's "death spiral" spin, for instance, one skater acts as the center of the circle while his partner rotates around him. He provides tension force, which acts upon his partner to initiate the centripetal force. The faster his partner spins, the more force is needed to keep her moving in a circle. His partner's inertia, or tendency to resist a change in motion, is based on her density; the higher the density, the greater the inertia. This move is best performed with a stronger and heavier center or pivot point to maintain the centripetal acceleration.
Individual Spins
Individual spins, like those performed during jumps, also rely on centripetal force. In this case, you do not use tension or an outside force to turn. Rather, you rely on the law of inertia -- an object in motion tends to stay in motion unless acted on by an outside force -- to spin on the ice or in the air. Density will affect your spin. Without a central tension force, you must consolidate your mass to help reduce your inertia. Spinning with your arms outstretched increases your inertia, slowing you down. Pulling your arms into your body increases your rotational speed.
Skating in Circles
Even skating in circles around a rink is considered centripetal acceleration. You are exerting a force -- in this instance, that force comes from your skates -- when you press your skate blade into the ice to initiate your movement. Tucking in your arms, leaning into your turn and increasing the force of your push increases your centripetal force.
References
- Encyclopedia: Centripetal Force
- Montana State University-Bozeman: Centripetal Force
- Real World Physics Problems: The Physics of Figure Skating
- The Physics Classroom: Motion Characteristics for Circular Motion
- Science Buddies: Tightening the Turns in Speed Skating: Lessons in Centripetal Force & Balance
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