The key to a successful coaster is to give the rider the thrill of speed and acceleration. It all comes down to speed control. To achieve this, the hills, curves, dips, straight aways, braking systems and loops are not randomly designed. They are carefully designed by engineers who have a deep understanding of the science of motion, properties of materials and structural design and a keen understanding of safety. The basic aspects of this science of motion are a central part of this demonstration.
Velocity is the speed of an object in a certain direction.
When direction changes, velocity changes. A ride at the amusement park may run at a constant speed, but its velocity is constantly changing when its direction of motion is changing. A roller coaster is called a coaster because once it starts it coasts through the entire track. No outside forces are required for most coasters. Roller coasters trade height for velocity and velocity for height.