This presence of speed is especially noticeable in today’s society, where there is a growing demand for immediacy. Obviously, speed is also intrinsically related to a multitude of physical phenomena. Somehow, everyone has an intuitive, more or less accurate idea of the concept of speed.
It is necessary to distinguish between average speed and instantaneous speed. Instantaneous speed is the speed that a body carries at a given moment, while average speed is the quotient between displacement and time.
Also, it should be noted that velocity is a scalar magnitude; that is, it has an address, a meaning and a module. In this way, velocity is applied in one direction.
In the international system, speed is measured in meters per second (m / s), although other units such as kilometers per hour (km / h) are often used in everyday life.
How to calculate?
The calculation of the average speed is performed using the following expression:
v m = ∆s / ∆t = (s f – s) / (t f – t )
In this equation, v m is the average velocity, ∆s is the increase in displacement, and ∆t is the increase in time. Conversely, s f sare the final and initial offset, respectively; while t f and t are the end and start time, respectively.
Another expression for calculating the average speed is:
v m = s t / t t
In this expression, s t is the total displacement and tt is the total time invested in carrying out this displacement.
As noted in this calculation, only the total displacement and the total time spent on it are taken into account, without the need to take into account how this displacement occurred.
It is also not necessary to know whether the body accelerated, stopped, or traveled the entire journey at a constant speed.
It may be necessary to perform the inverse calculation to determine the total displacement of the average speed and the total time taken.
In this case, you just need to clear the displacement of the first equation to get the expression that allows you to calculate:
∆s = v m ∆t
This can also be done if you need to calculate the time spent traveling at a known average speed:
∆t = v m ∆s
Speed measurement units
Speed can be expressed in different units. As mentioned earlier, in the International System the unit of measurement is the meter per second.
However, depending on the context, it may be more convenient or more practical to use other units. Thus, in the case of means of transport, the kilometer per hour is generally used.
On the other hand, in the Anglo-Saxon unit system, they use either the foot per second ( feet/s ) or the mile per hour ( mph ) for the mode of transport.
In maritime navigation, the knot is generally used; on the other hand, in aeronautics the Mach number is sometimes used, which is defined as the ratio between the speed of a body and the speed of sound.
Average Speed Calculation Examples
A typical example where you might need to calculate the average speed is a shift between two separate cities.
Suppose the total displacement (which need not match the distance between the two cities) taken on the route between the two cities (for example, 216 kilometers) as well as the time spent on that route is known. – for example, three hours.
The calculation of the average speed would be done like this:
v m = ∆s / ∆t = 216/3 = 72 km / h
If you want to express the speed in International System units, the following conversion must be performed:
v m = 72 km / h = 72 ∙ 1000/3600 = 20 m / s, since a kilometer is a thousand meters and an hour is 3600 seconds.
Another practical case of calculating the average speed is when several displacements were made in a certain period of time.
Suppose a woman who has taken several bike rides over several days wants to know the average total speed of her route.
The woman covered the following distances in the following days: 30 kilometers, 50 kilometers, 40 kilometers and 20 kilometers.
The respective times used were as follows: an hour and a half, two and a half hours, 2 and a half hours and an hour and a half. Then, the resulting average speed is calculated as follows:
v m = (30 + 50 + 40 + 20) / (1.5 + 2.5 + 2.5 + 1.5) = 17.5 km / h
Average speed examples
It might be interesting to know some examples of average displacement speeds to get a more intuitive idea of the different values that speed can take.
In the case of a person walking, the value of his average speed is considered to be 5 kilometers per hour. If that same person runs, he can reach half that average speed.
The average speed of an amateur cyclist can be estimated to be around 16 kilometers per hour, while for a professional cyclist the average speed reaches the value of 45 kilometers per hour.
Category 1 hurricanes can have an average speed of 119 kilometers per hour. Finally, the Earth’s average orbital speed around the Sun is 107,218 kilometers per hour.