# 1.2.3 Velocity-Time Graphs

### Velocity-Time Graphs: Basics

• A Velocity-time graph shows how the velocity (or speed) of an object changes over time Graph showing how the velocity (speed) of an object changes over time

• If the line is horizontal, the velocity is constant (no acceleration)
• If the line slopes upwards then the object is accelerating (speeding up)
• If the line goes down then the object is decelerating (slowing down)

### Calculating Distance

• The distance travelled by an object can be found by determining the area beneath the graph The distance travelled can be found from the area beneath the graph

• If the area beneath the graph forms a triangle (the object is accelerating or decelerating) then the area can be determined using the formula:
• If the area beneath the graph is a rectangle (constant velocity) then the area can be determined using the formula:
`area = ½ x base x height`
• If the area beneath the graph is a rectangle (constant velocity) then the area can be determined using the formula:
`area = base x height`

#### Exam Tip

When asked to find the distance, start by stating:

`distance = area beneath graph`

A common mistake is to try and find distance using the distance-speed-time equation. This equation will not work if the speed of the object is changing.

Extended Only

### Calculating Acceleration

• Lines that slope downwards have negative gradients and so can be said to have negative accelerations: This is the same thing as a deceleration
• If the gradient of the line changes then the acceleration of the body must be changing:
• A line with constant gradient represents constant acceleration (linear motion)
• A curved line represents changing acceleration – either decreasing (if the gradient gets smaller) or increasing (if the gradient gets large)

#### Exam Tip

Remember to include units when giving your answers. The units of acceleration, for example, are m/s2 ### Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
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