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.