Though we just got to witness the Olympics this past summer, it should not be forgotten that the Winter Olympics are just two years away. One of the most popular sports to watch is figure skating, not just for the beauty of the performances, but for the important laws of physics that underlie every move the skaters make.
The physics starts with the ice. One of the main reasons ice is a suitable surface on which to skate is its near lack of friction on the blades of the skates. The center of ice is made up of tightly crystallized water molecules, but on the surface, these water molecules are less tightly packed, forming a nearly liquid, frictionless surface. This allows the skates to glide along the ice, hardly losing any speed.
In order to glide along the ice, the skater must first generate a force to push themselves forward. The energy for this force is stored as chemical potential energy (ATP) in the muscle cells of the skater’s legs. When the skater extends their leg, pushing against the ice, this potential energy is converted into kinetic energy and they move forward.
Spinning is a common move in figure skating, and viewers are often puzzled at how fast skaters can make themselves spin without adding any extra pushing. Skaters spin faster because of conservation of angular momentum. When they start spinning and have their arms and/or leg extended, the radius of their spin is large. Their angular momentum is proportional to their radius as well as their speed, so by making their radius smaller by bringing their limbs toward their center, the speed must increase to keep momentum conserved.