1
$\begingroup$

I'm studying the principles of accelerometer and given below is what is stated in LiveScience

An accelerometer is an electromechanical device used to measure acceleration forces. Such forces may be static, like the continuous force of gravity or, as is the case with many mobile devices, dynamic to sense movement or vibrations. Acceleration is the measurement of the change in velocity, or speed divided by time.

So it says that it measures acceleration forces due to a static force, but how can a static force induce an acceleration on an object because a static force virtually keeps an object at rest.

An object at rest does not have an acceleration does it?

Improve this question
$\endgroup$
5
  • $\begingroup$ An accelerometer device itself does not have to be accelerating. It detects a force that can cause acceleration (static acceleration) or by detecting the amount of dynamic acceleration you can analyze the way the device is moving. The following link is titled a beginners guide to accelerometers. dimensionengineering.com/info/accelerometers Hope it helps. $\endgroup$
    – Bob D
    Commented Aug 28, 2020 at 15:21
  • $\begingroup$ The wikipedia article does not say that. The quoted text appears to be from livescience.com. $\endgroup$
    – David Hammen
    Commented Aug 28, 2020 at 15:23
  • $\begingroup$ What the wikipedia article on accelerometers says is "An accelerometer is a tool that measures proper acceleration. Proper acceleration ... is different from coordinate acceleration, which is acceleration in a fixed coordinate system. For example, an accelerometer at rest on the surface of the Earth will measure an acceleration due to Earth's gravity, straight upwards of g ≈ 9.81 m/s2. By contrast, accelerometers in free fall (falling toward the center of the Earth at a rate of about 9.81 m/s2) will measure zero." $\endgroup$
    – David Hammen
    Commented Aug 28, 2020 at 15:26
  • 3
    $\begingroup$ The LiveScience article uses "static" to mean non-changing, in contrast to its use of "dynamic" to mean changing. $\endgroup$
    – David Hammen
    Commented Aug 28, 2020 at 15:49
  • $\begingroup$ So it is not referring to static frictional force? $\endgroup$
    – SlayerDiAngelo
    Commented Aug 28, 2020 at 17:21

2 Answers 2

Reset to default
3
$\begingroup$

An object at rest does not have an acceleration does it?

At rest in what frame of reference? A universal inertial frame of reference does not exist.

What accelerometers measure is the acceleration due to the sum of all of the accelerations due to the real non-gravitational forces acting on an accelerometer. Accelerometers do not sense acceleration due to fictitious forces such as centrifugal acceleration and the Coriolis effect due to the Earth's rotation. Accelerometers do not sense acceleration due to gravity; no device can per Einstein's equivalence principle.

Consider an accelerometer at rest on the surface of the Earth. The forces acting on it from the perspective of an Earth-fixed frame of reference are gravity, centrifugal force, buoyancy by the air, and the normal force exerted by the Earth. The accelerometer does not measure gravitation or centrifugal acceleration. All that are left is the tiny buoyancy force and the much larger normal force. An accelerometer at rest on the surface of the Earth registers an acceleration of about one g, upward.

Next consider an accelerometer orbiting the Earth at an altitude of 6378 km. There's a tiny, tiny bit of air even that high, but it is so very sparse that atmospheric drag is essentially non-existent. Even the very best accelerometer will not be able to sense that tiny atmospheric drag. Solar radiation pressure also acts on the accelerometer, but this too is very small. The only other forces acting on this accelerometer are the gravitational force exerted by the Earth, the Sun, the Moon, other planets, etc. Accelerometers do not measure gravity. This accelerometer registers zero, or very close to zero.

Improve this answer
$\endgroup$
-1
$\begingroup$

Acceleration and Force are two different concepts. The first has S.I. Units m/s$^2$ and the second Newtons.

Accelerometers measure acceleration. Force sensors measure forces.

A static force (such as the force of gravity) is a force with constant magnitude. therefore a constant force induces a constant acceleration.

Improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.