Velocity

Terminology

Velocity is the rate of change of position. Considering constant velocities there is:

[2.1a]
or:
[2.1b]
or:
[2.1c]

Where is:
s - distance, t - time, v - velocity

Figure 1:

Distance vs. time plot

If an object moves with constant velocity, the resulting plot is a straight line. The slope of the line represents the speed.
Velocity is a vector physical quantity. The scalar absolute value (magnitude) of velocity is speed. Velocities are always given in relation to a fixed point or another object. Speeds of cars are given in relation to the earth's surface. If you would be inside a spaceship besides our planet, you could see the earth spinning around and you would add the track speed of the earth's surface to express the speed of the car. Those track speed varies from pole (0m/s) to equator (465m/s). Next you could realize that the earth is moving around the sun with a speed of 29,800m/s and that the sun is moving with a speed of 220,00m/s around the center of our galaxy and that our galaxy is moving in relation to other galaxies....
Nobody has found an absolute fixed point, velocities could refer to (yet). That is no problem for this project. For our needs it is sufficient to adopt the ground beneath our feet as reference point.

In practice

You can find some objects listed with their characteristic speed at the table below:

Object	v in m/s	Remark
Snail's pace	0,0008
Pedestrian	1,4
100m runner	10,44	Wold record of Usain Bolt in 9,58s at world championship in Berlin 2009
Carrier pigeon	13 - 27	They are slower the more they have to carry...
Truck	22	Speed limit for trucks with a weight of more than 2,8t in Germany. As a driver of compact cars I am wondering if the truckers know about that?!?!
Fiat 126	29	Maximum speed of a car with a 2-cylinder 17kW combustion engine.
Cheetah	30	Fastest creature on earth (without technical support).
Thrust SSC	341	Super Sonic Car: Fastest car with jet propulsion, equipped with two Rolls-Royce Spey turbines and afterburner. Remark of the author: "Wastage of energy!!!"

At the next page you will find a Java-application showing the correlations between speed, covered distance and used time; both in a plot and as a 2D simulation.
Play around with different values and see how the objects move in relation to each other. Fixed on the earth's surface are the guideposts at a distance of 50m between two of them. The observing camera is moving with the same speed as the vehicle does. To give you the impression of movement, the tires of the car are jumping while it is moving. If the car is passing the pedestrian, it looks like he is doing the "Moonwalk", sliding "backwards" contrary to the direction of travel. As told at the top of this page: "speeds are relative!"

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