RevisionSpeed:
You can calculate average speed using the equation: speed = distance ? time. Average speed cameras are used to find out if a motorist is driving too quickly. A distance-time graph shows how the distance of an object changes over time, and its speed.
Average speed
The speed of an object tells you how fast or slow it is moving. You can find the average speed of an object if you know:
The distance travelled
The time taken to travel that distance
You can calculate average speed using the equation:
Speed = distance ? time
Distance-time graphs represent how an object moves. They show how the distance moved from a starting point changes over time.
Calculating average speed
This equation shows the relationship between average speed, distance and time:
Average speed = distance ? time
For example, what is the average speed of a runner who covers 100 m in 10 sAverage speed = 100 ? 10 = 10 m/s
In science, average speed is usually given in metres per second, m/s. If you are given the distance in km, multiply it by 1000 to get the distance in m.
For example, a car covers 2 km in 100 s. What is its average speed2 km = 2 ? 1000 = 2000 m
Average speed = 2000 ? 100 = 20 m/sChanging speed:
Acceleration is the rate at which an object changes its speed. It is calculated using the equation:
Acceleration = change in speed ? time taken.
Speed-time graphs illustrate how the speed of an object changes over time. The steeper the gradient of the line, the greater the acceleration.
Velocity is speed in a particular direction. An object accelerates if its velocity changes.
Acceleration
In everyday language we use ‘accelerate’ to mean speeding up and ‘decelerate’ to mean slowing down. In scientific terms, positive acceleration means an increase in speed and negative acceleration means a decrease in speed.
Acceleration depends on two things:
How much the speed changes
How much time the change in speed takes
Calculating…