# Acceleration We accelerate when the light turns green

The speed or a velocity of an object is rarely constant. For example, it is extremely unlikely that you drive at a perfectly constant speed when you travel in your car. You have to pull out of your driveway and speed up to the speed limit. You will then have to stop at red lights and then start driving again when the light turns green. You constantly change your speed when you drive.

Acceleration is changing velocity. Velocity has two components:Speed and direction. If we change the speed of an object than the acceleration of that object will change. If we change the direction of an object than the acceleration of that object will change. If we change both speed and direction of an object than the acceleration of that object will change.

To properly measure the acceleration of an object we must also account for how quickly the object changes its velocity. If the object changes velocity quickly we can say it had a very great acceleration. So acceleration can be better described as how velocity changes over time. Or in otherwords, the rate at which velocity changes. Using symbols, this equation becomes: Where a is acceleration, v is velocity, t is time. The delta symbol before the v and t means “change in.” The unit for acceleration is m/s/s or m/s2

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