• A speed-time graph is used to describe the speed of an object and calculate its acceleration

Constant acceleration on a speed-time graph

• If an object is moving at a constant acceleration, the speed-time graph will be a straight line

  • If the constant acceleration is zero, the line will be horizontal

  • If the constant speed is non-zero, the line will have a gradient

• If an object has an acceleration of zero, the object is travelling at a constant velocity

  • Its velocity is not changing over time

  • If the constant speed is zero, then the object is stationary

The gradient of a speed-time graph represents the object's acceleration

• A steeper slope, or a higher gradient, represents a greater acceleration

• A shallower slope, or a lower gradient, represents a slower acceleration

• If the gradient is positive, the line slopes upward

  • A positive gradient represents an increasing speed, or acceleration

• If the gradient is negative, the line slopes downward

  • A negative gradient represents a decreasing speed, or deceleration