Richard Cardenas has taught Physics for 15 years. He has a Ph.D. in Physics with a focus on Biological Physics.
The most useful type of motion in physics is that of constant acceleration. In this lesson you will learn about constant acceleration, why it is important, and an example of motion that undergoes constant acceleration.
Definition of Constant Acceleration
Whenever the speed of an object changes, that object is said to be accelerating. Acceleration is defined as the rate that your speed changes, or how fast your speed is changing. This means that whenever you slow down or speed up, you are accelerating. Constant acceleration is an even more specific type of accelerated motion. An object that travels with constant acceleration has a speed that changes by the same amount each second. For instance, if the speed was 2 meters/second in the first second, 4 meters/second in the next second, and 6 meters/second in the third second etc., then the speed increases by a constant amount of 2 meters/second during each second. Therefore, the acceleration of the object is 2 meters/second/second (the units are also known as meters per second squared).
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The most useful example of constant acceleration is free fall. Free fall refers to the motion of an object that is either dropped from some height or thrown upward. The object is acted upon by the gravity of the Earth. For example, when you go out parachuting, the moment you jump from the plane but before you deploy your parachute, you are in free fall. Any object thrown or dropped near the surface of the Earth experiences the same constant acceleration, which is called acceleration due to gravity. This acceleration has a magnitude of approximately 10 meters per second squared and is directed down toward the Earth. The speed versus time graph shown below is for an object thrown upward. The object is acted upon by the gravity of the earth and experiences a constant acceleration of 10 meters per second squared.
The next graph shows the acceleration versus time for the same situation. The line is horizontal, which indicates that the acceleration is constant.
Graph Showing Constant Acceleration of -10 meters/second/second
These two graphs show the main features of constant acceleration: constantly increasing or decreasing speed from the first graph and a horizontal line in the second graph of acceleration versus time. Whenever your speed increases by the same rate, you are moving with constant acceleration.
Constant acceleration refers to motion where the speed increases by the same amount each second. The most notable and important example is free fall. When an object is thrown or dropped, it experiences a constant acceleration due to gravity, which has a constant value of approximately 10 meters per second squared. In physics, we find it easier to assume that acceleration is constant in order to make problem solving easier.
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