The state in which the speed of a body increases is called acceleration. When this speed increases in equal measure over equal time periods, it is called constant acceleration. When we say that the speed of a body increases in direct proportion to the passage of time, it means that the speed of a body increases equally over equal time periods.

Example :

When an Airplane flies in velocity of 250 meters per second (900 kilometers per hour), and after a minute it flies 280 m/s and after one more 310 m/s (1116 k/h), we say it moves in uniform acceleration. its velocity increases equally: Every minute its velocity increases in 30 meters per second.

Factor a is the acceleration, and it determines the speed added to the body over each time period.

In our example, the acceleration (a) is 0.5 meters per second squared -

The state in which the speed of a body decreases is called deceleration. The term acceleration is often also used to describe the behavior of a body decreasing its speed. In this case we say that the body has negative acceleration.

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