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#

Acceleration

As we will see in the next section, acceleration is a very important
concept in Newtonian physics.
Just as the velocity involves a rate of change of position in time,
the **acceleration** of an object describes the rate of change of
velocity. Also just as with velocity, there are two types of
acceleration. The first - the **average acceleration** - involves
the change in instantaneous velocity over a given time interval:

Note that, from now on, when we say ``velocity'', we will mean the
instantaneous velocity. As well as a size, acceleration also
involves a direction: for example, a car traveling on a
road that runs due north accelerates from rest at a stop sign to a
speed of 30 m/s in 10 seconds. That car experienced an average
acceleration
during that time of 30/10 m/s^{2} or 3 m/s^{2} with direction
due north. In terms of km/hr, 30 m/s is:

If the driver of the
same car notices a radar trap and slows down to the speed limit
of 60 km/hr, or about 17 m/s in, say 5 seconds, then the car undergoes
an average acceleration **due south** of 17/5 m/s^{2} = 3.4
m/s^{2}. In this case, the car is slowing down, or decelerating. Objects
with a large acceleration
change their velocity quickly over time.
We can also define the **instantaneous acceleration**
at a point **A**
as the limit of the average acceleration between **A** and
a nearby point **B**
as the interval between **B** and **A** becomes zero:

From now on, when we say ``acceleration'' we will mean the
instantaneous acceleration.

** Next:** Graphing Motion
**Up:** Motion
** Previous:** Velocity
*modtech@theory.uwinnipeg.ca *

1999-09-29