Uniform circular motion is the motion of an object traveling at a constant speed on a circular path. The period T is the amount of time required to travel once around the circle, that is, to make one complete revolution. The definition of uniform circular motion emphasizes that the speed or the magnitude of the vector is constant. The direction is not constant either. Centripetal acceleration occurs when the acceleration points towards the center.

Acceleration is the change in velocity divided by the elapsed time. Centripetal acceleration is a vector quantity and has both a direction and magnitude. The direction is towards the center of course. When an object is released from a path of circular motion, it continues to move in a straight line. During centripetal acceleration, the object is constantly accelerating towards the center. The smaller the radius of the circular path is, the smaller the centripetal acceleration. An object in uniform circular motion can never be at equilibrium.

The net force causing centripetal acceleration is called centripetal force. The centripetal force points in the same direction as the centripetal acceleration- towards the center. The direction of this force is constantly changing. This net force is the sum of all the force components that point along the radial direction. The smaller the circular arc is, the smaller the centripetal force required to produce the centripetal acceleration must be. Greater speeds and tighter turns require greater centripetal forces.

When a car moves around a curve, the static friction between the road and the tires provides the centripetal force to keep the car on the road.

When a car travels without skidding around an un-banked curve, the static friction between the road and the tires provides the centripetal force to keep the car on the road. However, here in the US, curves are banked. The angle at which a friction-free curve is banked depends on the radius of the curve and the speed at which the curve is to be negotiated. Greater speeds and smaller radii require more steeply banked curves, or larger angles.

Although there are many satellites in orbit, the ones in circular orbits have uniform circular motion. These satellites are kept on path by a centripetal force provided by the gravitational pull of the Earth. There is only one speed that a satellite can have if it is to remain in an orbit with a fixed radius. The closer the satellite is to Earth, the smaller the radius of the orbit will be. The orbital speed must be greater as well.

For a given orbit, a satellite with a large mass has exactly the same orbital speed as a satellite with a small mass.

The condition of apparent weightlessness is similar to what occurs in an elevator during its free-fall. In a falling elevator, apparent weight is zero. This is because everything moves in uniform motion. If there was a scale in the elevator, with a person standing upon it, the persons force upon the scale would be zero, because both the objects are moving downward, and cannot push on each other. Objects in uniform circular motion constantly accelerate, or "fall" towards the center of the circle, in order to remain on the circular path. Therefore, the apparent weight in a satellite is zero.

The surface of the rotating object pushes on any objects it contacts, and thereby provides the centripetal force that keeps the object moving on a circular path.

When the speed of travel on a circular path changes from moment to moment, it is said to be nonuniform. But, there are four points on a vertical circle where the centripetal force can be identified easily. At each point, the centripetal force is the net sum of all the force components oriented along the radial direction and pointed toward the center of the circle.

Imagine a motorcyclist riding around a vertical loop. As the cycle goes around, the magnitude of the normal force changes. This is because the speed changes and because the weight does not have the same effect at every point. At the bottom, the normal force and the weight oppose one another. At the top, the normal force and weight reinforce one another. At points 2 and four on the sides, the weight is tangent to the circle and has no component pointing towards the center. If the speed at each of these four places is known, along with the mass and radius, the normal forces can be determined.