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Acceleration

Acceleration is a measure of how the velocity of an object is changing over time. It can be found by computing the difference in velocities at first one time, then some time later, and dividing that by the difference in time. The units, then, are length per time divided by time, or length divided by time squared (m/s² or ft/s^2,). If a car goes from 0 mph to 60 mph in 2 minutes (1/30 of an hour), then the acceleration of the vehicle is 1800 miles per hour squared (60 mph - 0 mph divided by 1/30 hr = 1800 miles/hr²)! If the car continued to accelerate at this value for an hour, its velocity at the end of the hour would be 1800 mph!

However, if the same car is traveling at 60 mph when it passes a mileage marker, and it maintains its velocity to pass the next mileage marker one minute later (velocity equals 1 mile divided by 1/60 hr = 60 mph), then the acceleration is equal to zero (60 mph - 60 mph divided by 1/60 hr = 0 mph)! In other words, when the velocity doesn't change over time, the acceleration for that time period is zero. Engineers compute accelerations that are both increasing (positive) and decreasing (negative). This rate of slowing down is often called deceleration.

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