The physics concepts involved in a luge run are fairly basic:
- Force and inertia are required to get the slider moving at the start of the course.
- Gravity pulls the slider and the sled down the track.
- Friction between the sled and the track works against gravity and is a prime determining factor in speed.
- Aerodynamic drag acts on the slider/sled combination to resist its motion through the air. The lower the drag, the higher the speed.
- G-force is equal to the force exerted by gravity. It is the force acting on a body that is accelerating. If a slider is facing 3 Gs through a turn, their body feels three times heavier than their actual weight when they are at rest.
At the start of the course, the slider/sled unit is at rest. The slider's goal is to begin the run with the utmost speed, so they need to propel the sled onto the course with as much force as possible to overcome its inertia (its desire to remain at rest).
If the slider weighs 198 pounds (89 kilograms), and the sled weighs 50.6 pounds (23 kilograms), that's a combined mass of about 247 pounds (112 kilograms). By rocking back and forth at the top of the track, the slider needs to generate enough momentum to propel 247 pounds through the first 10 feet (3 meters) of the course in about two seconds to achieve a good start.
As the slope begins, the slider lies down on the sled and lets gravity take over. In luge, heavier weight means faster speed. The heavier the weight of the athlete, the greater the force of gravity pulling them down the track. One of the forces standing in the way of gravity is friction. To reduce the amount of friction between the sled and the track, the steels on the sled are polished with things like sandpaper and diamond paste.
Another force acting against the pull of gravity throughout the run is aerodynamic drag, which consists of air friction and form drag. In luge, when air runs over the top of the slider, it interacts with the materials of the helmet and racing suit. This results in air friction. To reduce air friction, racing suits are slippery and skin-tight, and the visor on a luge helmet is rounded and extends all the way under the slider's chin so there are no air pockets. The interaction between the air and the frontal shape of the slider/sled combination results in form drag.
In addition to using the most aerodynamic shapes for the sleds, the slider tries to further minimize form drag by maintaining an aerodynamic body position. The less area they present, the better. Even lifting their head an inch to see the track increases drag and can add several thousandths of a second to their run time.
In doubles luge, the taller athlete lies in front, between their partner's legs, to achieve a smoother profile. Many sliders spend hours training in wind tunnels to find the ideal body position to minimize drag.
Probably the most physically battering points on a luge run are the turns, and especially the turn combinations, when G-forces increase. Acceleration and deceleration throughout a luge course put an average force of up to 3 Gs on a slider's body. Forces can reach up to 5 Gs in banked turns, when centripetal force adds another dimension to the forces acting on the slider.
Centripetal force pulls the slider outward in the turn. To maintain speed, the slider must perfectly balance the centrifugal force with the force of gravity pulling them downward through the course. This means finding the "sweet spot" and staying there. If the forces are balanced, the sled will smoothly move through each turn and back into the straightaways. If they are unbalanced, the slider will have to steer too much, slowing down the run.
With so much at stake in so little time, luge athletes train all year to shave a few thousandths of a second off their time. In the next section, we'll find out what's involved in luge training.