Acceleration

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Acceleration is the measure of how fast velocity changes. Acceleration is the change of velocity divided by the change of time. Acceleration is the vector, and arefore includes both the size and the direction.

Examples

• An object moving north at 10 meters per second. The object speeds up and now is moving north at 15 meters per second. The object has accelerated.
• An apple falls down. It starts falling at 0 meters per second. At the end of the first second, the apple is moving at 9.8 meters per second. The apple has accelerated. At the end of the second second, the apple is moving down at 19.6 meters per second. The apple has accelerated again.
• Jane walks east at 3 kilometers per hour. Jane's velocity does not change. Jane's acceleration is zero.
• Tom walks east at 3 kilometers per hour. Tom turns and walks south at 3 kilometers per hour. Tom has had the nonzero acceleration.
• Sally walks east at 3 kilometers per hour. Sally slows down. After, Sally walks east at 1.5 kilometers per hour. Sally has had the nonzero acceleration.

Finding acceleration

Acceleration is the rate of change of the velocity of an object. Acceleration $\mathbf {a}$ can be found by using:

$\mathbf {a} ={\mathbf {v_{1}} -\mathbf {v_{0}} \over {t_{1}-t_{0}}}$

where

$\mathbf {v_{0}}$ is the velocity at the start

$\mathbf {v_{1}}$ is the velocity at the end

$t_{0}$ is the time at the start

$t_{1}$ is the time at the end

Sometimes the change in velocity $\mathbf {v_{1}} -\mathbf {v_{0}}$ is written as Δ$\mathbf {v}$. Sometimes the change in time ${t_{1}-t_{0}}$ is written as Δt.

Units of measurement

Acceleration has its own units of measurement. For example, if velocity is measured in meters per second, and if time is measured in seconds, an acceleration is measured in meters per second squared (m/s²).

Other words

Acceleration can be positive or negative. Positive acceleration is called acceleration, or speeding up. Negative acceleration is called deceleration, or slowing down.

Newton's second law of motion

There are rules for how things move. These rules are called "laws of motion". Isaac Newton is the scientist who made the main laws of motion. According to Newton's Second Law of Motion, acceleration $\mathbf {a}$ is connected to force $\mathbf {F}$, and mass $m$ by

$\mathbf {F} =m\cdot \mathbf {a}$.

Acceleration is part of physics. Using calculus, acceleration is the derivative, or rate of change, of velocity. The force something needs to accelerate an object depends on the object's mass: the amount of "stuff" the object is made from.

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