Related topics: physical activity

How accurate are dog-activity trackers?

There are countless gadgets available these days for people to track everything from our heart rate to our stress levels. So perhaps it's no surprise that there also are quite a few products that now claim to similarly monitor ...

Building a wireless micromachine

All around us, hiding just outside our range of vision, are miniscule machines. Tiny accelerometers in our cars sense a collision and tell the airbags to inflate. A Nintendo Wii controller's tiny gyroscopes translate your ...

Detecting disease in beef cattle using ear tag units

A smartphone switches its orientation from portrait to landscape depending on how it's tilted. A car's airbags inflate when it senses collision forces. By detecting earth's vibrations, a computer can measure the magnitude ...

Smart phones spot tired drivers

An electronic accelerometer of the kind found in most smart phones that let the device determine its orientation and respond to movement, could also be used to save lives on our roads, according to research to be published ...

Bio-inspired eye stabilizes robot's flight

Biorobotics researchers at the Institut des Sciences du Mouvement - Etienne-Jules Marey (CNRS/Aix-Marseille Université) have developed the first aerial robot able to fly over uneven terrain that is stabilized visually without ...

Measuring earthquake shaking with the Community Seismic Network

In 2011, the Community Seismic Network (CSN) began taking data from small, inexpensive accelerometers in the greater Pasadena area. Able to measure both weak and strong ground movement along three axes, these accelerometers ...

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An accelerometer is a device that measures proper acceleration, also called the four-acceleration. This is not necessarily the same as the coordinate acceleration (change of velocity of the device in three-dimensional space), but is rather the type of acceleration associated with the phenomenon of weight experienced by a test mass that resides in the frame of reference of the accelerometer device. For an example of where these types of acceleration differ, an accelerometer will measure a value when sitting on the ground, because masses there have weights, even though they do not change velocity. However, an accelerometer in gravitational free fall toward the center of the Earth will measure a value of zero because, even though its speed is increasing, it is in a frame of reference in which it is weightless.

An accelerometer thus measures weight per unit of (test) mass, a quantity of acceleration also known as specific force, or g-force (although it is not a force, and these quantities are badly-named). Another way of stating this is that by measuring weight, an accelerometer measures the acceleration of the free-fall reference frame (inertial reference frame) relative to itself (the accelerometer). This measurable acceleration is not the ordinary acceleration of Newton (in three dimensions), but rather four-acceleration, which is acceleration away from a geodesic path in four-dimensional space-time.

Most accelerometers do not display the value they measure, but supply it to other devices. Real accelerometers also have practical limitations in how quickly they respond to changes in acceleration, and cannot respond to changes above a certain frequency of change.

Single- and multi-axis models of accelerometer are available to detect magnitude and direction of the proper acceleration (or g-force), as a vector quantity, and can be used to sense orientation (because direction of weight changes), coordinate acceleration (so long as it produces g-force or a change in g-force), vibration, shock, and falling (a case where the proper acceleration changes, since it tends toward zero). Micromachined accelerometers are increasingly present in portable electronic devices and video game controllers, to detect the position of the device or provide for game input.

Pairs of accelerometers extended over a region of space can be used to detect differences (gradients) in the proper accelerations of frames of references associated with those points. These devices are called gravity gradiometers, as they measure gradients in the gravitational field. Such pairs of accelerometers in theory may also be able to detect gravitational waves.

This text uses material from Wikipedia, licensed under CC BY-SA