Velocity

The velocity of an object is the rate of change of its position. If the position of an object is some function of time, then the velocity is the derivative of that function:

<math>v(t)={\mathrm{d}x \over \mathrm{d}t}</math>

where x is the position and v is the velocity. The velocity is a vector, and its length or absolute value is called the speed. The velocity has dimensions of length / time, and may thus be expressed in meter per second (in scientific usage). In daily life, miles per hour and kilometers per hour are more common units.

If an object's acceleration and velocity have the same sign, the object is gaining speed. If acceleration and velocity have different signs, the object is losing speed.

If velocity is zero, acceleration is not necessarily zero. If acceleration is zero, velocity is not necessarily zero.