# 15. Describing motion in a distance-time graph

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## Describing the motion in a distance time graph

When we describe the motion of an object, we must use the language of physics: is the object moving at a constant speed, accelerating or decelerating, or is the object stationary (at rest)?

We've already seen that an upwards straight line means that the object is moving forwards at a constant speed. However, what about an upwards curving line? For each second that ticks by on the horizontal time axis, the distance travelled is greater than the second before. In other words, distance is increasing at an increasing rate. We say that the object is accelerating.

If the line on a distance-time graph curves the other way (when the gradient becomes flatter), then the object will be decelerating, as each second the distance travelled is less than the previous second.

As before, a flat line (gradient equals zero) means that the object is stationary (at rest).

GCSE Physics Keywords: Constant speed, Accelerating, Stationary, Curved, Straight, Gradient, Slope, Forwards, Backwards

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