Velocity is the rate of change of position in a given direction. It is a vector quantity, meaning it has both magnitude and direction. Speed is the magnitude of velocity. A car going 60 mph north has a velocity. A car going 60 mph has a speed. The distinction matters when direction changes. A car going around a track at constant speed has changing velocity, because its direction is changing. That change in velocity is acceleration. Velocity is measured in meters per second in the SI system.

Velocity is not the same as speed. Speed is a scalar. Velocity is a vector. Average velocity is displacement divided by time. Displacement is the change in position, which is a vector. Instantaneous velocity is the velocity at a specific moment. It is the derivative of position with respect to time. Velocity is a key concept in kinematics, the study of motion. It is also important in dynamics, the study of forces and motion. Newton's laws are often written in terms of velocity and acceleration. Momentum is mass times velocity. Kinetic energy depends on the square of speed, which is the magnitude of velocity. Velocity is one of the most fundamental quantities in physics.

Velocity facts

• Definition. Rate of change of position with direction.
• Vector. Has magnitude and direction.
• Units. Meters per second (m/s).
• Average. Displacement divided by time.
• Instantaneous. Velocity at a specific moment.

Velocity is not the same as speed. Speed is scalar. Velocity is a vector.