If you or I jump into the air as high as possible, we can get off the ground for about half a second. Michael Jordan could stay on top almost one second. Despite the fact that the Winter Olympics are many events in which athletes perform athleticism and strength, being high in the air, none blur the line between jumping and flying as much as the springboard.
I teach students about sports physics. Springboard jumping is perhaps one of the most intriguing events at the Winter Games to showcase physics in action. The winner is the athlete who travels farthest and who flies and lands with the best style. By turning their skis and bodies into what is essentially a wing, ski jumpers are able to fight gravity and stay in the air for five to seven seconds as they travel on the length of the football field through the air. So how do they do it?
How to fly
Three basic concepts from physics play in the springboard: gravity, lift and resistance.
Gravity pulls any object in flight down to the ground. Gravity acts on all objects equally, and athletes can do nothing to reduce its action. But when moving athletes also interact with the air. It is this interaction that can cause the lifting force, which is the upward force created by the push of air on an object. If the force created by the lifting force roughly balances the force of gravity, the object may slide or fly.
To create lift, the object must move. When moving an object through the air its surface collides with air particles and pushes these particles from the path to the object. As air particles are pushed down, the object is pushed up according to Newton’s third law a movement that says that for every action there is an equal and opposite reaction. The air particles that push the object upwards create a lifting force. Increasing the speed as well as increasing the surface area will increase the lifting force. The angle of attack – the angle of the object relative to the direction of air flow – can also affect the rise. Too steep and the object will stop, too flat and it will not press on the air particles.
While all of this may seem complicated by sticking your hand out of a car window, these principles are perfectly illustrated. If you keep your hand perfectly straight, it will stay more or less in place. However, if you tilt your hand so that the bottom is facing the direction of the wind, your hand will be pushed up when air particles collide with it. That is the rise.
The same collisions between the object and the air, which provide lift, also cause drag. Dragging prevents the forward movement of any object and slows it down. As the speed decreases, the lifting force also limits the duration of the flight.
For springboard jumpers the goal is to use careful body positioning to maximize lift and minimize drag.
During great jumps, athletes maximize lift and glide long distances.
Skiers start high on the slope, then ski down to create speed. They minimize resistance by squatting and gently steering to reduce friction between the ski and ramp. When they reach the end, they can go 60 miles per hour (96 km / h).
The ramp ends at the take-off point, which, if you look closely, is actually in a slight decline angle of 10 degrees. Just before the athletes reach the end of the ramp, they jump. The ski slope is designed to mimic the path a jumper will take so there will never be more of them 10 to 15 feet above the ground.
As soon as the athletes are in the air, the fun physics begins.
Jumpers do their best to create as much lift as possible while minimizing resistance. Athletes will never be able to create enough lift to completely overcome gravity, but the more lift they create, the slower they will fall and the further down the slope.
To do this, athletes align their skis and bodies almost parallel to the ground and place the skis in a V-shape directly outside the body. This position increases the surface area that creates the lifting force, and puts them in the perfect angle of attack, which also maximizes the lifting force.
As the resistance reduces the skier’s speed, the lifting force decreases and the gravity continues to pull the jumper. Athletes will start falling faster and faster until they land.
The rules correspond to physics
With so much physics in play, there are many ways like wind, choice of equipment and even an athlete’s own body can affect how far a jump can go. So that everything was fair and safe, there is many rules.
While observing the events, you may notice that officials are moving the starting point up or down the slope. This adjustment is made based on wind speed, as faster headwinds will result in greater lift and will result in longer jumps that can pass past a safe landing area.
The length of the skis is also adjustable and tied to the height and weight of the skier. Skis maximum can be 145% skier growth and skiers with a body mass index less than 21 should have shorter skis. Long skis are not always the best, as the heavier the ski, the more lift you need to do to stay in the air. Finally, skiers should wear tight-fitting suits ensure that athletes will not use their clothing as an additional source of lift.
If you are in the mood for the Olympics to marvel at the physical strength of athletes, take the time to also consider their mastery of the concepts of physics.
Written by Amy Pope, a senior lecturer in physics and astronomy at Clemson University.
This article was first published in Conversation.
https://scitechdaily.com/ski-jump-physics-flying-or-falling-with-style/ Fly or fall with style?