Only speed can be a factor that attracts many sports fans competitions in bobsleigh, sledding and skeleton at this year’s Winter Olympics in Beijing. But under the exciting descents on the winding, ice-covered track play a lot of concepts from physics. This is how athletes respond to physics, which ultimately determines the fastest runs from the rest of the group.
I study sports physics. It’s easy to miss much of the thrill of sledding – athletes ’movements are often too small to be noticed as they fly, looking no more than a blurry spot on your TV. It would be easy to assume that competitors are just falling or sliding down the track at will. But that thought just scratches the surface of all the subtle physics that goes into a performance that has won gold medals.
Gravity and energy
Gravity is what makes sledges go down ice-covered tracks in bobsleigh, sled and skeleton competitions. The physics of the big picture is simple – start at a certain height and then go down to a lower height, allowing gravity to accelerate athletes to speed approaching 90 miles per hour (145 km / h).
This year’s race is held at Yanqing National Sliding Center. The track is about a mile long (1.6 km), falls to a height of 397 feet (121 meters) – and the steepest section is an incredible 18% – and consists of 16 curves.
Riders in sledding competitions reach their high speed due to the conversion of potential gravitational energy into kinetic. Gravitational potential energy is the accumulated energy and increases when the object rises farther from the Earth’s surface. Potential energy is converted into another form of energy as soon as the object begins to fall. Kinetic energy is the energy of motion. The reason a flying baseball breaks glass when it hits a window is that the ball transfers its kinetic energy to the glass. Both gravitational potential energy and kinetic energy increase with increasing weight, which means that a bobsled team of four has more energy than a sleigh or single-person skeleton for a given speed.
Racers deal with a lot of kinetic energy and strong forces. When athletes enter a turn at 80 mph (129 km / h), they experience acceleration that can reach five times greater than the usual acceleration of gravity. While bobsleds, sleds and skeletons may look lightweight, in fact they are not the only ones.
Most trails are about a mile long (1.6 km), and athletes cover that distance in just under a minute. The final time is calculated by adding the four runs together. The difference between a gold medal and a silver medal in the men’s sledding category at the 2018 Winter Olympics was only 0.026 seconds. Even small mistakes made by the world’s best athletes can cost a medal.
All athletes start at the same height and follow the same track. Thus, the difference between gold and the disappointing result is not due to gravity and potential energy, but due to the quick start, maximum aerodynamic and shortest path down the track.
While gravity pulls athletes and their sleds down, they are constantly faced with air particles that create a force called air resistance that pushes athletes and sleds in a direction opposite to their speed. The more aerodynamic the athlete or team, the greater the speed.
To minimize resistance from the air, sled riders – standing face up – lie as flat as possible. The same is done by riders-skeletons facing down. Whether in a team of two or four people, bobsleders remain tightly clamped inside the sled to reduce the area available for air strikes. Any mistakes in body positioning can make athletes less aerodynamic and lead to a small increase in time, which can cost them medals. And these mistakes are hard to fix with high accelerations and running forces.
The shortest way down
In addition to being as aerodynamic as possible, another significant difference between fast and slow running is the way racers go. If they minimize the overall length of their sled and avoid zigzag movement on the track, the riders cover a shorter distance. In addition to just not having to go that far to cross the finish line, shortening the path means less air resistance and less loss of speed from friction on the track.
Fans often miss the intricacies of turning and steering. There are sledges for all activities steel blades called runners. Bobsleigh has two sets of runners that come in contact with the ice. The front rider stretches rings attached to pulleys that rotate the front guides. Sled runners have curved bows in front where the riders lay their eggs. By moving the head and shoulders or bending the calves, athletes can turn the sled. Skeleton riders do not have these controls and should bend the sledge himself using his shoulders and knees to start the turn. Even a small movement of the head can cause the skeleton to deviate from the optimal path.
All of these subtle movements are hard to see on television, but the consequences can be serious – excessive driving can lead to a collision with a track wall or even an accident. Improper steering can lead to bad turns that cost racers time.
While it may seem like riders just glide on an icy track at high speed after moving, a lot more happens. Spectators will need to pay close attention to the athletes on these fast-moving sleds to discover interesting facets of physics in action.
Written by John Eric Goff, Professor of Physics at Lynchburg University.
This article was first published in Conversation.
https://scitechdaily.com/the-high-speed-physics-of-how-bobsled-luge-and-skeleton-send-humans-hurtling-at-incredible-speed/ High-speed physics of how bobsleds, sleds and skeletons send people to incredible speeds