HowStuffWorks of the Day - 13/2/2006: How Bobsledding Works

ndmmxiaomayi

13 Feb 06, 18:44

Introduction to How Bobsledding Works

If you've ever hit a patch of ice while driving your car, you've experienced a very tiny piece of what driving a bobsled is like. On an icy road, there's almost no friction between your tires and the road surface, so you can't steer very well. And any sudden moves, like hitting the brake, can send you spinning out of control.

So imagine if your car were open at the top and back, like a bobsled, and that the patch of ice lasted for almost a mile. It's not a mile of straight, level road, either -- it's full of dramatic curves and downhill most of the way. That's what being in a bobsled is like. Drivers and crew plummet down a hill on a track, or run, that's full of twists and turns. A wrong move can cause a dramatic crash.

ndmmxiaomayi

13 Feb 06, 18:46

The Team

Racing a bobsled requires three things -- a team, a bobsled (or bob) and a track. The team includes either two or four athletes who steer, brake and add to the overall weight of the bobsled. The bob has an aerodynamic design and smooth runners so it can go as fast as possible. The track, generally made of concrete, has a solid ice surface. On the way down, bobsleds reach speeds of 80 miles an hour (130 Kph), even around curves. Crashes are common.

It's easy to guess that being a bobsledder requires bravery and a good sense of balance. But making it down the run requires more than just coordination and nerve. Bobsleds weigh hundreds of pounds. The driver and brakeman (and the crewmen or push athletes in four-man teams) have to get the bob moving from a complete stop. They have to run as fast as they can, then jump inside the bob before the first curve. They also have to withstand extreme gravitational forces during the race.

For these reasons, most bobsledders have backgrounds in other strenuous sports, like American football or track and field. During try-outs, prospective members have to prove their abilities in sprinting, jumping, pulling and lifting. Training isn't limited to taking a bobsled down a frozen run -- there's lots of running, jumping and lifting weights. Crewmen and brakemen in particular do a lot of weightlifting, since they shoulder most of the burden for getting the bob going.

Without any traction on the ice, it would be impossible for the team to move the bob. So, everyone on the team wears spiked start shoes for better traction. The spikes are arranged like a brush, and they can be no longer than one millimeter, no wider than four millimeters and no farther apart than three millimeters. Bobsledders also wear skintight, aerodynamic suits to help reduce drag on the way down the run. Everyone on the team must wear a protective helmet, usually with a full-face visor or a pair of goggles. Most drivers wear gloves, but some go barehanded for better contact with the steering rings.

ndmmxiaomayi

13 Feb 06, 18:52

The Bobsled

Modern bobsled races are competitions between two-person or four-person teams. Bobsleds have the same basic components whether they are built to hold two or four athletes. Each bob has:

The Federation Internationale de Bobsledding et de Tobogganing (FIBT) sets rules for the composition and dimensions of each of these components, as well as the total weight of bobsleds. Bobsled manufacturers work closely with bobsled teams and designers to make the best sled design.

Each type of bob has a minimum weight when empty and a maximum weight with bobsledders and their equipment. Weight limits for bobsleds are:

Heavier sleds go faster, so teams that do not reach the maximum occupied weight may add ballast to make their bob heavier. Officials weigh the sleds at the end of the run to make sure they meet the weight requirement.

According to FIBT rules, bobsleds can have decorations and sponsor logos, much like race cars. The fiberglass hull cannot be transparent or fragile enough to break upon impact with part of the track. Hulls are typically made in two pieces, but steering comes from the front runners, not from movement in the hull.

The runners themselves are blunt. They're polished until very smooth, minimizing the friction between them and the ice. Since narrow runners further reduce friction and are faster, the FIBT has rules covering runner width. Applying plating, coating or lubricant to the runners is illegal, as is heating them. Race officials electronically measure the temperature of the runners before the race and compare it to a reference runner that has been exposed to air for at least an hour. A temperature difference of more than four degrees between the bob's and the reference runner results in disqualification.

Until the 1960s, bobsledders used a steering wheel to steer the bob. Now, drivers pull steering rings to change directions. These rings attach to a rope-and-pulley system that connect to the front runners, which can move about 3 inches (7.62 centimeters) to the left or right. The driver pulls the left ring to turn left and the right ring to pull right. The brake, located at the end of a lever between the brakeman's knees, stays in place until after the bob crosses the finish line.

ndmmxiaomayi

13 Feb 06, 20:50

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:

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 40 kilometers per hour (24.8 mph).

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.

ndmmxiaomayi

13 Feb 06, 20:52

Bobsledding History

Bobsledding began in 1877 in Davos, Switzerland, when people added a steering wheel to a normal sled. The first bobsledding club formed in 1897 in St. Moritz, Switzerland. Most of the first bobsled runs were snow-covered roads, and for years it was a popular recreational sport, particularly for the wealthy. It had the sort of popularity that skiing has today. The sport's name comes from the way early teams bobbed their heads to try to gain more speed on straight portions of the run.

Bobsledding has been an Olympic event since the first Winter Olympic Games in 1932. At that time, the only competition was a four-man race. Two-man events were added in 1932. Only men competed at the Olympic level until the 2002 games in Salt Lake City, when two-woman teams began competing. The only Winter Olympic Games that have not included bobsledding were the 1960 games in Squaw Valley, California, when too few teams expressed interest in competing.

Until the 1950s, most bobsledders were big and brawny. But in 1952, new rules governing the maximum weight of a bobsled and its passengers went into effect. At that point, bobsledders became highly-trained athletes who were very strong but light enough to fit the rules' weight requirements. Teams from all over the world have competed in bobsledding, including those from countries known for their warm climates, like Jamaica and Puerto Rico.