Velocity

Velocity isn’t the same as speed: it’s the speed of an object in a given direction. This means that if the direction in which an object is moving changes, its velocity changes even if its speed doesn’t. The term used to explain a change in velocity is accelerates.

The velocity of a moving object can be plotted in a velocity-time graph.

• – The slope of the line is the acceleration. The acceleration is greater the steeper the slope is.
• – If the gradient of the slope is negative then this shows deceleration.
• – The distance travelled is represented by the area under the line of the graph. The bigger the area is, the more distance travelled.

HIGHER TIER

You should be able to calculate gradients on velocity-time graphs.

The gradient is the acceleration of the object. This is where the line is sloping upwards. As with a distance-time graph, to calculate the gradient of a line divide the change in the vertical axis by the change in the horizontal axis.

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Acceleration

If an object is travelling in a straight line and with a constant acceleration then you can figure out the acceleration of the object if you know by how much it velocity changes and how long it takes for this to occur.

Acceleration can be calculated with the following equation:

acceleration = change in velocity / time taken for the change

• – acceleration is measured in metres per second squared (m/s²)
• – change in velocity is measured in metres per second (m/s)
• – t is measured in seconds (s)

The change in velocity can be calculated by:

change in velocity = final velocity – starting velocity

If the value of acceleration is a negative then this means the objects is slowing down or decelerating.