As you learned in the previous section, displacement helps us understand motion. In this section, you are going to look at another type of motion, constant velocity.

What does motion with a constant velocity look like?

Time-elapsed photo of cars on a highway

Source: Nederlands: Snelweg A7 tijdens de avondspits, Uberprutser, Wikimedia Commons

Velocity is the rate of change of position. It is measured in meters per second (m/s). If an object is moving with constant velocity, it is always moving in the same direction and at the same speed. It is important to note that velocity and displacement can be positive or negative depending on the direction the object is moving compared to the frame of reference of the motion. Most scientists use the following convention:

Positive Velocity or Displacement Negative Velocity or Displacement
Away from the observer
Toward the observer

Examples of this type of motion include a car driving on the highway, an airplane flying at its cruising altitude, or light traveling through the atmosphere.

Mathematically speaking, this type of motion can be described with one equation and two graphs. You will look at and use the equation in the next lesson. Now, let’s take a look at the graphic representation of constant velocity.

The graphs typically looked at are position vs. time (sometimes displacement vs. time) and velocity vs. time. In all cases, the velocity of the object is the same as the slope of the position vs. time graph.

The following two examples show the graphs that are related to constant velocity. These examples show three graphs, but most scientists ignore acceleration vs. time because it is a flat line at zero.

Link to video segment. Assistance may be required. Constant Positive Velocity

Link to video segment. Assistance may be required. Constant Negative Velocity