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Acceleration
From Wikipedia, the free encyclopedia
In physics, acceleration is defined as the rate of change of velocity, or, equivalently, as the second derivative of position (with respect to time). It is thus a vector quantity with dimension length/time². In SI units, acceleration is measured in meters/second² (m·s-²). The term "acceleration" generally refers to the change in instantaneous velocity.
In common speech, the term acceleration is only used for an increase in speed. In physics, any increase or decrease in speed is referred to as acceleration and similarly, motion in a circle at constant speed is also an acceleration, since the direction component of the velocity is changing. See also Newton's Laws of Motion.
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After completing his theory of special relativity, Albert Einstein realized that forces felt by objects undergoing constant proper acceleration are indistinguishable from those in a gravitational field. This was the basis for his development of general relativity, a relativistic theory of gravity.
This is also the basis for the popular Twin paradox, which asks why one twin ages more rapidly when moving away from his sibling at near light-speed and then returning, since the aging twin can say that it is the other twin that was moving. General relativity solved the "why does only one object feel accelerated?" problem which had plagued philosophers and scientists since Newton's time (and caused Newton to endorse absolute space). In special relativity, only inertial frames of reference (non-accelerated frames) can be used and are equivalent; general relativity considers all frames, even accelerated ones, to be equivalent. (The path from these considerations to the full theory of general relativity is traced in the Introduction to general relativity.)
The formula for acceleration, when force is constant, is 
(Final Velocity - Initial Velocity / Total Time Taken)
it should also be pointed out that:
The expression (Final position - Initial Position) / Total time taken)
is, in fact, velocity.
Putting it all together means:
, where a is acceleration, v is velocity, y is position, and t is time.
- Serway, Raymond A.; Jewett, John W. (2004). Physics for Scientists and Engineers, 6th ed., Brooks/Cole. ISBN 0-534-40842-7.
- Tipler, Paul (2004). Physics for Scientists and Engineers: Mechanics, Oscillations and Waves, Thermodynamics, 5th ed., W. H. Freeman. ISBN 0-7167-0809-4.
- Acceleration and Free Fall - a chapter from an online textbook
- Trajectories and Radius, Velocity, Acceleration on Project PHYSNET
- Science aid: Movement
- Physics Classroom: Acceleration
- Science.dirbix: Acceleration
- Acceleration Calculator
- Motion Characteristics for Circular Motion
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