Acceleration
Acceleration
is defined as the change in velocity over timehow much an object speeds
up or slows down. ("Deceleration" is the term usually used to
describe negative accelerationslowing down.) Velocity is the rate, or
speed, at which an object moves over time. Mathematically, velocity is
defined as the distance traveled divided by the time taken to travel that
distance. For instance, an airplane that travels 50 feet in one second
has a velocity of 50 feet per second, or v = 50 ft/sec. Velocity is often
expressed in miles per hour or kilometers per houran automobile travels
60 miles per hourit takes it one hour to travel a distance of 60 miles.
Acceleration
is the change in velocity divided by the time taken to make the change.
For example, if an airplane's speed increases from 50 ft/sec to 60 ft/sec
and it takes five seconds to make that change, the change in velocity
during this time is 10 ft/sec (60 ft/sec  50 ft/sec). To find the acceleration,
we simply divide this change (10 ft/sec) by the time it takes to make
this change5 seconds: "10 divided by 5 is 2."
As
for the units, ft/sec divided by seconds is the same as multiplying by
1/sec, which results in ft/(s x s) or ft/s2. So, the acceleration of the
airplane is 2 ft/sec2. Acceleration is also a vector, meaning it has a
value and a direction.
Therefore,
to calculate the acceleration of a car going from 0 mph to 60 mph in 10
seconds, we must first convert miles per hour to feet per second in order
to divide the change by 10 seconds. By performing the computations to
convert miles to feet and hours to seconds, we are left with the appropriate
velocity in ft/sec.
We
now divide 88 feet/second by the amount of time taken to make the change,
which was 10 seconds. 88 ft/sec divided by 10 seconds shows the acceleration
to be 8.8 ft/sec2.
The
method is the same when using the metric system: meters replace feet and
kilometers replace miles (using the correct conversion factors for actual
distances).
