The everyday concept of speed arises when we consider how quick or slow a body moves. Somehow we relate the displacement of the body with the time spent in such displacement. In this section, we are going to define what is meant in physics by average speed and its difference with average velocity.

## Average speed

**Average speed** of a body that moves from point P_{1} to point P_{2} is defined as the * ratio* of the

**and the corresponding**

*distance traveled**. It is given by the expression:*

**elapsed time**where:

- ${V}_{\mathrm{avg}}$ :
**Average speed**in the interval studied. The unit of measurement in the*International System*(S.I.) is meter per second (m/s) - $\u2206s$ :
**Distance traveled**in the interval considered. Measured over the*trajectory*. The unit of measurement in the*International System*(S.I.) is the meter (m) - $\u2206t$ :
**Time**taken by the body to go from*P*to_{1}*P*. The unit of measurement in the_{2}*International System*(S.I.) is the second (s) *s*,_{1 }*s*:_{2}**Distance traveled**by the body on the trajectory from the beginning of the motion to*P*, and from the beginning of the motion to_{1}(s_{1})*P*. The unit of measurement in the_{2}(s_{2})*International System*(S.I.) is the meter (m)*t*,_{1}*t*:_{2}**Time**in which the body is found in the initial point*P*and in the final point_{1}*P*respectively. The unit of measurement in the_{2}*International System*(S.I.) is the second (s)

**Average speed** is a **scalar magnitude** as opposed to average velocity which is a vector. The ** unit of measurement in the International System (S.I.)** of the

**average speed**is the

**meter per second (m/s)**. On the other hand, unlike average velocity, which depended on the vectors of the initial and final positions of the motion, the

**average speed**depends on the distance traveled over the trajectory. Therefore,

*a body in motion will always have an average speed greater than 0*. In general, the ${V}_{\mathrm{avg}}\ge \left|\overrightarrow{{v}_{\mathrm{avg}}}\right|$ is satisfied, and both values will be the same in the case of rectilinear motion without change of direction.