Speed and velocity

Speed, distance and time

Distance is how far an object moves. It does not include an associated direction, so distance is a scalar quantity.

Speed is the rate of change of distance – it is the distance travelled per unit time. Like distance, speed does not have an associated direction, so it is a scalar quantity.

Typical speeds

When people walk, run, or travel in a car their speed will change. They may speed up, slow down or pause for traffic. The speed at which a person can walk, run or cycle depends on many factors including:

  • age
  • terrain
  • fitness
  • distance travelled

Some typical values for speed in metres per second (m/s) include:

Method of travelTypical speed in m/s
walking1.5
running3
cycling6
car13 - 30
train50
aeroplane250

It is not only moving objects whose speed can vary. The speed of the wind and the speed of sound also vary. A typical value for the speed of sound in air is about 330 m/s.

The velocity of an object is its speed in a particular direction. Velocity is a vector quantity because it has both a magnitude and an associated direction. To calculate velocity, displacement is used in calculations, rather than distance.

Unlike distance, which is a scalar quantity, displacement is a vector quantity. It includes:

  • the distance travelled, measured in a straight line from start to finish
  • the direction of the straight line