These graphs also show if the object is moving at a constant speed or accelerating, going back to the starting point, or stationary. Constant speed is shown by a straight rising line.

Calculations involving speed, distance and time The distance travelled by an object moving at constant speed can be calculated using the equation: distance travelled = speed × time s = vt ...

You know you can’t reach the speed of light for a massive object, so the naive thought that “50% the speed of light + 50% the speed of light = 100% the speed of light” has to be wrong.