Acceleration
In
physics or physical science, acceleration is defined as the rate of change of velocity. It is thus a vector quantity with dimension length/
time. In SI units, acceleration is measured in meters/second using an
accelerometer.
Encyclopedia
In
physics or physical science,
acceleration is defined as the rate of change of velocity. It is thus a vector quantity with dimension length/
timeē. In SI units, acceleration is measured in meters/secondē using an
accelerometer.
Explanation
To accelerate an object is to change its velocity, which is accomplished by altering either it's speed or direction in relation to time. In this strict mathematical sense, acceleration can have positive and negative values. Any time that the sign of the acceleration is the same as the sign of the velocity, the object will speed up. If the signs are opposite, the object will slow down. Acceleration is a vector defined by properties of magnitude and direction. When either velocity or direction are changed, there is acceleration .
Acceleration is defined technically as "the rate of change of velocity of an object with respect to time" and the instantaneous acceleration of an objection is given by the equation
where
- a is the acceleration vector .
- v is the velocity
- t is time
- d is Leibniz's notation for differentiation
When velocity is plotted against time on a
velocity vs. time graph, the acceleration is given by the slope, or the
derivative of the graph.
If used with SI standard units this equation gives
a the units of m/, or m/sē .
An average acceleration, or acceleration over time,
a can be defined as:
where
- u is the initial velocity
- v is the final velocity
- t is the time interval elapsed between the two velocity measurements
Transverse acceleration 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 standard acceleration of free fall or 9.80665 m/sē, roughly caused by the
gravity of
Earth at
sea level at about 45.5°
latitude.
Jerk is the rate of change of an object's acceleration over time.
In
classical mechanics, acceleration is related to force and
mass 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.
It should be known that when comparing the forces between 2 or more objects, the Force = m multiplied by the acceleration.
Relation to relativity
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 that also explained how gravity's effects could be limited by the speed of
light.
If you accelerate away from your friend, you could say 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.
General relativity solved the "why does only one object feel accelerated?" problem which had plagued philosophers and scientists since Newton's time . In
special relativity, only inertial frames of reference 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 . Therefore, frames of reference must include a description of their local spacetime
curvature to qualify as complete.
References
External links
