# Speed, Distance, Time and Acceleration

Acceleration & speed are physical concepts that we encounter every day and it is crucial to understand these concepts in most areas of physics. we think of speed as something we have when moving and this forms the basis of speed definition.

Velocity can be defined as the rate of change in distance. what exactly does that mean? well, it means that an object’s speed is a measure of how long it takes terms of time for it to travel a given distance. from this we get the following equation speed equals distance divided by the time the standard units of distance in meters and time in seconds because this speed is measured in distance per time for example meters per second or kilometers per hour.

Let’s look at an example. a car traveled 100 kilometers in two hours what was its speed? so 100 divided by 2 equals 50 kilometers per hour. now you try a sprinter who runs 100 meters in 12.5 seconds. did you get 8 meters per second and another one a jet can travel at 350 meters per second how far will it travel at this speed in 30 seconds pause and have a think.

Well, it travels 350 meters in one second so in 30 seconds it will travel 30 times 350 which equals 10,000 500 meters. so how far will it travel in three minutes pause and have a think. well, 3 minutes is 3 times 60 or 180 seconds so the distance it will travel is 180 times 350 which equals 63,000 meters or 63 kilometers.

In the same way, that speed is the rate of change in distance acceleration is the rate of change in speed. this means that the acceleration of an object is a measure of how much its speed changes over a given period of time. to calculate acceleration we use the following equation acceleration is equal to the change in velocity divided by time.

Let it try an example. the velocity of a bus increased from 0 to 18 meters per second in 6 seconds calculate its acceleration. so acceleration equals final velocity minus initial velocity over time. another example is a hungry cheetah who saw a gazelle and decided to chase it. the cheetah was walking at five meters per second and accelerated to 20 meters per second in five seconds what was its acceleration? pause the article or you work it out.

The sign in front of an object’s acceleration indicates whether the object’s speed is increasing or decreasing. if an airplane’s acceleration is negative 40 meters per second squared its speed is decreasing.

The gradient of a line on a speed-time graph represents acceleration if the gradient is positive or goes up the object has a positive acceleration. if the gradient is reduced, the object will have a negative acceleration or deceleration.

What’s the acceleration of this object between points a and B. the change in speed is 25 minus 5 which equals 20 the change in time is 6 minus 2 which equals 4. so the acceleration is 20 meters per second over 4 seconds which equals 5 meters per second the second. is the acceleration large small or zero in these turn graphs and is it positive or negative?

So that’s how speed and acceleration are related and can be calculated.