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About
Acceleration:
In
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 lightspeed 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 (nonaccelerated
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 spacetime curvature
to qualify as complete. The rate of change of acceleration is
known as jerk or jolt.
An
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 or school.
Improve
on this project by building your own accelerometers!
A
protractor,
string and weight can be used to measure horizontal acceleration.
See the following activity. Here is an excellent
activity that uses this principle.
To
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
For
more ideas search Google:
