Many fans view ice skating as one of the most artistic sports. Indeed, the graceful precision required to execute split-second timing of turns and jumps is something even a novice to the sport can appreciate. The artistry of a skater's motions make her appear to float over the ice in a delicate dance. It's strange, then, to consider how a sport so steeped in the arts could be so beneficial to the analytic world of science. As a science project, ice skating is very demonstrative when viewed through the lens of classic physics.
Items you will need
- Moderately skilled skater
- Video camera
- Skating rink
- Heavy bag
Demonstrating Newton's First and Third LawsStep 1
Record a video of a skater as she stands stationary on the ice.
Explain to your audience that this demonstrates Newton's First Law, which states that "every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it." Relate that since the skater is not moving, she is in a state of zero motion and will tend to stay that way until an external force is applied.
Instruct the skater to perform a single push with her skate.
Record a closeup of the skater's foot on video as she pushes against the ice, zooming out to show that the skater begins moving slightly, then returns to rest.
Describe to your audience that the skater demonstrates Newton's Third Law, which states that "for every action there is an equal and opposite reaction" and that it requires an external force to put her in motion and that she stays in motion until acted upon by an outside force.
Explain to the audience that the outside force is the reaction force of the ice, pushing against the skater who pushed against it. Also explain that the skater stayed in motion until acted upon by the external friction of the ice, which slowed the skater until she stopped.
Demonstrate Newton's Second LawStep 1
Tell your audience that Newton's Second Law states that the relationship between an object's mass, its acceleration and the applied force is stated as "force equals mass times acceleration" and that this means that for a given force a more massive object will not accelerate as much.
Place the yardstick on the ice in a lengthwise orientation parallel to the direction of the skating. Instruct the skater to perform a single, hard push, starting at one end of the ruler so you can measure her movement. Make sure that the skater maintains an orientation parallel to the yardstick.
Film the distance she travels. Repeat this several times until you acquire a fairly steady average distance.
Instruct the skater to repeat the single kick at the same strength but this time holding the heavy bag. Record the distance traveled for several trials. You will note that the average distance traveled has dropped.
Explain that moving a greater mass with the same force causes our weighted skater to accelerate less, meaning she takes less time for friction to stop, thus causing her to travel less distance, confirming Newton's Second Law.
Demonstrating Conservation of Angular MomentumStep 1
Instruct the skater to begin a slow spin with her arms fully extended. Tell her not to kick or add rotation again unless she feels like she will fall.
Film the skater as she spins, noting how much she moves with each push and the speed of rotation with her arms extended.
Explain to your audience that a skater is an example of a system of rotational inertia, and, like any system, the skater's body will attempt to maintain equilibrium between the speed of rotation and the distribution of mass.
Instruct the skater to tuck her arms close to her body in the midst of a spin. Make sure to record the sudden increase in rotational speed, even though she is not adding any force.
Describe to your audience that as the skater pulls in her arms, the mass of the system is confined to a smaller area, meaning that the only way the system can conserve inertia is to rotate faster. Additionally describe that this is done without the addition of any other force, simply because the system seeks to achieve equilibrium.
Tips & Warnings
- Choose a time or skating location where other skaters will not interfere with your project, either by skating into or out of your work area or by creating noise while you are recording.
- Consider utilizing video effects capability to create an overlay that describes the principles as they are being demonstrated, putting force diagrams over the video.
- Ensure that your skater is competent enough to perform all of the required maneuvers safely before attempting this video.
- Ensure that your heavy bag for the Second Law section is full of soft materials to minimize risk to the skater if she falls down while carrying it.
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