Uniformly accelerated motion, or constant acceleration, is motion that has a constant and unchanging velocity. Uniformly accelerated motion may or may not include a difference in an object's speed.

The acceleration of an object means that there is a net force in the direction of that object's acceleration. Additionally, the object sometimes, but not always, has a change in speed. An object that falls in a vacuum under gravity's pull, for instance, is said to have a uniform acceleration and a change in speed. In contrast, a planet that orbits the sun in a circular path with no change in speed still has uniform acceleration but without an accompanying change in speed.

**Acceleration and Velocity**

In physics, acceleration is a type of vector quantity. It is described by scientists as the rate, or speed, in which an object's velocity changes. A change in velocity means an object is accelerating. A car that speeds up from 60 miles per hour to 80 miles per hour, for example, is accelerating. A change in speed is essential for a change in velocity. A car that travels at a constant rate of 70 miles per hour, for instance, has no change in velocity. Velocity is measured as the rate at which an object changes speed, but it is not a measure of speed itself. For instance, an object traveling at a speed of 80 miles per hour does not necessarily have a different velocity than an object that is moving at a rate of 30 miles per hour. A car that is traveling at a speed of 80 miles per hour is moving fast, but it is not accelerating unless there is a change in its speed. Whenever the car's velocity changes, it is said to be accelerating.

**Accelerated Motion**

Accelerated motion is called constant acceleration. It is defined as the change when an object changes its velocity by the same amount each second. An object with a constant acceleration, however, does not necessarily have a constant velocity. An object accelerates, or speeds up, if it changes its velocity each second, regardless of whether its change in velocity is constant or variable. A car that speeds up from 80 miles per hour to 90 miles per hour over the course of 10 seconds, for instance, has constant velocity, while a car that goes from 80 miles per hour to 90 miles per hour at differing rates during the course of 10 seconds has a varying velocity. An object with a constant velocity, in contrast, is not accelerating even though it might be traveling at a speed of 80 miles per hour.

**Calculating Accelerated Motion**

Because objects always change their velocity, it is rare that an object falls at a truly constant rate of acceleration. An object in a free-fall, for example, usually accelerates as it falls. While it travels a certain distance to get from one point to the next, it may change its speed as it travels through the air. For example, the object might fall at a rate of five miles per hour one second and 10 miles per hour the next second. To calculate the object's average rate of acceleration, physicists use a special formula. Physicists can also determine the rate at which an object is losing speed, or decelerating, using the formula.