# Velocity and Acceleration

Velocity and acceleration are two key terms that describe an object's motion. In physics and everyday life the position of an object says very little about what the object is doing. Even describing a change in position says very little about the actual motion of the object. It is therefore important that when describing motion in physics we not only think about the change in position of the object, but also the distance, time and direction in which that change occurs. In order to explain the motion of an object in terms of position, time, and direction, we use velocity and acceleration.

## Velocity

Velocity is the change in an object's position with respect to time and direction. Velocity is measured by taking an objects change in position divided by the time it took to change that position:
The standard scientific units for velocity are meters (distance) divided by seconds (time). The final component in explaining an object's velocity is including a relative direction. For example, a car that travels 100 meters in 10 seconds, in the westerly direction, would have a velocity of 10 m/s west.

## Acceleration

Acceleration is the change in velocity of an object with respect to time. Acceleration is measured by taking the change in velocity of an object divided by the time is took to change that velocity:
The standard scientific units for acceleration are meters per second squared (m/s^2). Since acceleration is a measurement of change in velocity, it should be obvious that it must also include the direction in which the acceleration is occuring. For example, if a car is completely stopped, with an initial velocity of 0 m/s, and begins traveling east, and after 10 seconds is traveling 75 m/s, that car would have an acceleration equal to 7.5 m/s^2 east.

## Other Equations

There are several equations that relate velocity, acceleration and position. The main equations are listed below:

• s = the displacement (sometimes denoted R or x)
• u = the initial velocity (speed in a given direction)
• v = the final velocity
• a = the constant acceleration
• t = the time taken to move from the initial state to the final state