Equation to Measure Velocity

Velocity

• Velocity is similar to speed, but with one crucial difference: It is a vector quantity, so you must take direction into account. The average velocity of an object is defined as the displacement of that object divided by the time it took for the object to be displaced. Displacement is simply the distance the object moved in a particular direction. The units of velocity are meters per second.

Object Moving With Constant Velocity

• If the object is moving with constant acceleration, you can calculate its average velocity by dividing the change in displacement by the time elapsed: velocity = [x(final) -- x(initial)]/(change in time). To find the change in displacement, take the coordinates of the final position (or distance if working in one dimension) and subtract from the coordinates of the starting position. For example, if a car had moved 10 meters in a straight line in the "x" direction in five seconds, it would have a velocity of 10/5 = 2 meters per second.

Object Moving With Constant Acceleration

• If the object is accelerating, you can work out its average velocity over its whole path. To do this, you need to know its initial and final velocities. The object's average velocity is the sum of its initial and final velocities divided by 2: average velocity = [v(initial) + v(final)]/2. For example, if you drop a ball so that its initial velocity is 0 and it hits the ground with a velocity of 4 meters per second, its average velocity is 2 meters per second.

Object With Variable Acceleration

• If the object's acceleration is changing, it is a little more tricky to calculate its velocity. Variable acceleration can be expressed as a polynomial function --- an equation containing additional terms containing variables with indices greater than 1. In the case of velocity, the extra terms are multiplied by time to the power of 2, 3 or higher. In the simplest case, velocity = v(initial) + (b x time) + (c x time squared), where "b" and "c" are constants that determine the acceleration. If you know the initial velocity, the time elapsed and the constants, you can work out the object's average velocity.