Speed measures how fast an object is moving, whereas acceleration is how much the speed of an object changes during a specified period of time. If an object is speeding up, it has a positive acceleration, whereas an object slowing down has a negative acceleration.
To calculate the speed of an object, the distance traveled is divided by the time taken to travel that distance. If an object is gaining or losing speed, it is said to be accelerating.
Speed, unlike acceleration, cannot be negative. This is because speed is a scalar quantity, which means it does not include the direction an object is moving. Acceleration is a vector quantity, which means it shows how fast an object is changing speed and the direction in which the speed is changing.
Acceleration is calculated by finding the change in speed over a period of time, and then dividing this change by the time taken. If an object has a constant acceleration, it is speeding up by the same amount over a set period of time.
For example, if a car that is stationary speeds up to 10 mph in five seconds, the change in speed is 10 mph. The acceleration is found by dividing this number by five seconds, giving a value of 2 mph squared.