physics, acceleration (symbol: a) is defined as the rate of change (or time derivative)
of velocity. It is thus a vector quantity with dimension length/time². In SI units,
this is metre/second². To accelerate an object is to change its velocity over
a period of time. In this strict scientific sense, acceleration can have positive
and negative values—respectively called acceleration and deceleration (or retardation)
in common speech—as well as change of direction. Acceleration is defined technically
as "the rate of change of velocity of an object with respect to time" and is given
by the equation where a is the acceleration vector v is the velocity vector expressed
in m/s t is time expressed in seconds. This equation gives a the units of m/(s·s),
or m/s² (read as "metres per second per second", or "metres per second squared").
An alternative equation is: where is the average acceleration (m/s²) is the initial
velocity (m/s) is the final velocity (m/s) is the time (s) Transverse acceleration
(perpendicular to velocity) causes change in direction. If it is constant in magnitude
and changing in direction with the velocity, we get a circular motion. For this
centripetal acceleration we have One common unit of acceleration is g, one g being
the acceleration caused by the gravity of Earth at sea level at 45° latitude (Paris),
or about 9.81 m/s². In classical mechanics, acceleration is related to force and
mass (assumed to be constant) by way of Newton's second law: As a result of its
invariance under the Galilean transformations, acceleration is an absolute quantity
in classical mechanics. After defining his theory of special relativity, Albert
Einstein realized that forces felt by objects undergoing constant acceleration
are indistinguishable from those in a gravitational field, and thus defined general
relativity (which also resolved how gravity's effects could be limited by the
speed of light, but that is another story). A key point of general relativity
is that it 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). Simply put, if you hop in your car and accelerate
away from your friend, you could say (given your frame of reference) that it is
your friend who is accelerating away from you, although only you feel any force.
This is also the basis for the popular Twin paradox, which asks why only one twin
ages 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. 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. With changing velocity, accelerated objects exist in warped
space (as do those that reside in a gravitational field). Therefore, frames of
reference must include a description of their local space-time curvature to qualify
as complete. The rate of change of acceleration is known as jerk or jolt.
accelerometer or gravimeter is a device for measuring acceleration
and the effects of gravity. According to the principles of general relativity,
the effects of gravity are equivalent to those of acceleration, so an accelerometer
can make no distinction between these effects. Accelerometers are used in inertial
guidance systems, as well as in many other scientific and engineering systems.
Commercial accelerometers use
complex applications to measure acceleration. It is also possible though to measure
acceleration using very simple devices that can be easily constructed at home
on this project by building your own accelerometers!
and weight can be used to measure horizontal acceleration. See the following activity.
Here is an excellent
activity that uses this principle.
measure vertical acceleration a homemade spring scale with a weight attached can
be used. In effect this is the simplest form of accelerometer. See an excellent
activity that uses this principle
more ideas search Google: