Describe when an object is said to be speeding up on a velocity versus time diagram.

A horizontal line on a speed-time graph represents a constant speed.

Explanation:

Acceleration is defined by a sloping line on a speed-time graph. The sloping line shows the object's speed is increasing. The target either accelerates or slows down.

Velocity-time graphs are being used to illustrate the acceleration for moving objects in a horizontal path. You can use them to display momentum and to sort out movement.