The Physics of Bobsledding
Winning a bobsled race starts long before the push-off stretch — it starts with the design of a fast, efficient bobsled. A good bobsled has to take advantage of the physical forces that help it accelerate, and it has to minimize the forces that slow it down.
Acceleration due to gravity is the same for all of the bobsleds in the race — it's the physical constant of 9.8 meters per second squared. Drag, friction and momentum, on the other hand, all vary based on bobsled design and can affect how much the bob actually accelerates. The strongest, fastest, most skilled team in the world cannot compensate for a bob design that ignores these factors:
- Drag: Air passing around the bobsled creates drag, which slows the bobsled down. Wind tunnels and computer simulations help teams design bobsleds that are as aerodynamic as possible, cutting down on drag and helping the bobsled go faster.
- Friction: There's not much friction between smooth metal and ice, but even a tiny amount will slow the bob down. For this reason, fast bobsleds have very smooth runners that are as thin as possible while still meeting IBSF requirements. Each bob's runners scrape and scar the ice on the way down, so teams that race later in the day have more friction to overcome.
- Momentum: An object's momentum is its mass times its velocity. The more massive an object is and the faster it goes, the more momentum it has. The more momentum it has, the harder it is to stop. So, bobsleds with lots of momentum can more easily overcome the affects of drag and friction. A team that combines a good push-off with a bob that is very close to the maximum allowed weight has an advantage for the rest of the race.
A team with a fast bobsled has to do several things to win a race with it. The team must have a good push-off — this contributes to both speed and momentum. The team has about 54 yards (50 meters) to move the sled from a complete stop to a speed of around 24 miles per hour (40 kilometers per hour).
Getting the sled moving is harder than keeping it moving. This is because static friction (the friction between a motionless object and the surface it's resting on) is greater than sliding friction. Drivers need every advantage when steering, so they often start pushing only after the bob is moving to keep from exhausting themselves.
After the push-off, gravity and momentum take over, accelerating the bobsled downhill. The driver has to choose a path down the run very carefully. Steering too high on a curve adds to the total distance the bob has to travel, making the trip take more time. A driver who steers too low loses the advantage of centrifugal force that keeps the bob going during banked curves.
In the end, all of these physical forces and athletes' actions lead to a very tight race. Often, the winning team's time is only a few hundredths of a second faster than that of the second-place team.