Center of mass: The point in an object around which the mass is balanced. If you were to balance the bobsled on your finger, that point is the balance point, which isn’t always right in the middle.
Drag: The slowing down of something as it moves through air, water, or other fluid, which causes friction. A race car experiences drag because of air pushing against it as it goes around the track.
Friction: The force that slows objects down when they are rubbing against each other. Some things make lots of friction, like brakes on a tire, and some make very little friction, like skates on ice.
Kinetic energy: Energy of motion. A bobsled sliding down its track has kinetic energy.
Momentum: The amount of mass in motion. An object’s momentum depends on how much matter (its mass) is moving and how fast it’s moving. A boulder speeding down a mountain has much more momentum than a marble rolling slowly across the floor, and would require much more energy to stop it. (For older participants: momentum is the product of an object’s mass and its velocity.)
Potential energy: Stored energy. Anything that can move but isn’t has potential energy. A bobsled right before it starts down its racecourse has potential energy.
GUIDANCE FOR YOUNGER CHILDREN
Engineering Connections
Early bobsleds were similar to wooden sleds used by children. The pilot steers the metal runners in front, and the person in the rear operates the brakes. Credit: German Federal Archive.
Bobsled engineers keep coming up with new ways to make bobsleds faster and safer. For example, bobsleds used to be made out of wood. Now they are made out of fiberglass on a steel frame, which makes them stronger and lighter. Engineers also design bobsleds for speed, which accounts for their bullet shape. After all, what’s faster than a speeding bullet?
Engineers think about safety for bobsled riders, too. They have designed tracks with high sides so that the sled stays on the track and doesn’t fly off. The walls are curved in a way that helps prevent the sled from flipping over.
Science Connections
Successful bobsledding depends on two types of forces: gravity and friction. Friction is a force produced when two objects rub against each other and is constantly working against their motion. In this case, the sled rubs against the track. Bobsled tracks are made of ice, which doesn’t produce much friction because it is so slippery. But the air around the sled also causes friction because the sled is moving so fast. You can feel this friction when wind blows into your face while you’re sledding down a hill. The design of the bobsled reduces the amount of friction from both the track and the air.
GUIDANCE FOR OLDER YOUTH AND ADULTS
Engineering Connections
While much of a bobsled team’s success depends on the skill of the riders and the precise navigation of the team’s drivers, success also depends on the engineering and design of the sled. In 2014, BMW partnered with the US Bobsled Federation to redesign the sled for better speed. BMW engineers used aerodynamics to come up with the best design. The result? In 2014, at the Sochi Winter Olympics, Team USA took home its first medal in two-man bobsledding since 1952. Aerodynamics is the study of the flow of air as it passes over and around a moving object and of the forces the air makes on an object. The BMW engineers built on their knowledge of racecar aerodynamics to finesse their bobsled designs, which included shifting the center of gravity to allow for tighter steering.
Science Connections
For one bobsled to succeed over another, it must have a higher velocity, or speed, as it goes down the hill. This means that the bobsled team must maximize the amount of force that propels the sled forward and minimize the amount of force that works against the motion of the bobsled. Without a motor to propel it forward, the sled depends on gravity to keep it moving, as well as a running push from the team at the very top of the hill. Heavier bobsleds have more potential energy, and therefore more kinetic energy when they get moving. Modern bobsledding has weight limits on the sled and riders, so it’s hard to get a weight advantage today. The key to winning is to overcome the forces that would otherwise decrease the bobsled’s velocity, such as friction and drag.
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