Speed

In our everyday life, we all deal with different sorts of speed. We go to school or to work. If we are on foot, we move with relatively slow speed. If we take the bus (tram, underground, car), we already move with higher speed. In the summer time, we fly on holidays. With the plane, we travel very fast.

But What Is Speed Exactly?

The physics quantity velocity (v) is the ratio of a distance covered by a body (s) to the time taken (t):

When you walk, you move with a speed of approximately 5 km/h. If you ride in a car or bus, you move about ten times as fast, namely at approx. 50 km/h. (In the city, that is. On an ordinary road or a motorway you would go faster still). And with a plane you even reach a speed of about 800 to 950 km/h. Speed is measured with a speedometer, which is installed in every car, plane, etc. The police measure the speed of passing cars with a laser gun to determine if the speed limits are observed.

What happens when you have to stop the car or when the plane lands?

Then the speed changes, and for this change of speed there is a physics quantity as well - acceleration. Acceleration (a) is defined as the change of speed (v) divided by the time taken (t)

Acceleration is given in kilometres per hour per hour (km/h.h) or in metres per second per second (m/s.s). Therefore, an acceleration of 2 m/s.s means that the speed changes by 2 m/s every second, so that you accelerate 2 m/s every second. On the other hand, an acceleration of -2 m/s.s means, that you slow down by 2 m/s every second.

For racing cars it is very important to obtain high acceleration, since the racing drivers want to change the speed from 0 km/h to sometimes more than 300 km/h as quickly as possible.