Richard Cardenas has taught Physics for 15 years. He has a Ph.D. in Physics with a focus on Biological Physics.
In this lesson you will learn the definition of constant velocity, its important properties, and the equation that represents it. You will also see examples or applications of constant velocity.
What is Constant Velocity?
Velocity gives us information about the rate of change of your position, meaning how fast your position is changing per unit time. In physics, velocity is defined as the displacement divided by time where displacement is defined as the difference between your final and initial positions. Furthermore, when an object travels the same distance every second, then the object is said to be moving with constant velocity. This means that the magnitude of the velocity (or speed) and the direction of the velocity both remain constant.
Constant velocity has units of distance per time. The velocity gives you information about the rate of change of your position or how fast your distance is changing per unit time. The table below lists the common units of velocity.
meters per second
km/h or kph
kilometers per hour
mi/h or mph
miles per hour
Constant velocity is a vector. A vector is a quantity that requires both a magnitude and direction to fully describe the quantity. For velocity, the magnitude refers to how fast the object is moving (refer to the units listed in the table above). For direction, you may use any of the geographical directions (North, South, East, or West) and a positive sign or a negative sign (to represent up or to the right and down or to the left, respectively). An angle may also be used to give velocity direction.
Velocity may also be represented in a diagram as an arrow like the one illustrated in the figure below. The magnitude of the vector is the length of the arrow, and the direction of the vector is where the arrow is pointing (which is 47 degrees North of East in this figure).
Velocity is defined as displacement over time. The displacement refers to the difference between your final and initial positions. The time refers to how long it took to get from your initial to your final position. Below is the equation for velocity.
In your physics lab, you are asked to take a meter stick and put a mark on the floor of a long hallway in one meter intervals for a total of 8 meters. Eight of your classmates stand at each of the marks on the floor holding digital stopwatches. Your group is instructed to start their watches when you release a battery-operated car and to stop their watches as soon as the car passes their respective marks. The information is put in a table and graphed.
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The data table and the position versus time graph above show that the toy car was moving with constant velocity. The car covered each one meter distance in the same amount of time (0.65 seconds). The velocity can be calculated using the equation shown above where the displacement is 8 meters over a period of 5.20 seconds. Therefore, the velocity is 8 meters/5.20 seconds which is 1.54 meters/second. This data table and graph below show that the velocity of the toy car was constant. The velocity column was calculated by dividing the distance by the time.
Recorded Time (s)
Velocity versus Time Graph (Constant Velocity)
Another example of constant velocity can be illustrated by the cruise control function of your car. You are driving at 75 mph on a straight and flat highway when you decide to use the cruise control function. What cruise control does is to keep your velocity constant until you decide to either speed up (by stepping on the gas pedal) or slow down (by hitting the brakes). When cruise control was engaged, you were traveling with a constant velocity.
Velocity is a vector quantity, so it has a magnitude and direction. In order for the velocity to be constant, the magnitude of the velocity (or speed) and the direction of the velocity must not change. Therefore, an object that travels with constant velocity covers the same distance during each time interval and moves in the same direction during the same time interval.
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