Save guides, add subjects and pick up where you left off with your BBC account. A horizontal line means the object is moving at a constant speed. The gradient of the line = the rate of change of ...

Velocity-time graphs show how the velocity (or speed) of a moving object changes with time. These graphs also show if the object is moving at a constant speed or accelerating, decelerating, or ...

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.