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 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.