Specific force ( SF ) is a mass-specific quantity defined as the quotient of force per unit mass .
93-533: The g-force or gravitational force equivalent is mass-specific force (force per unit mass), expressed in units of standard gravity (symbol g or g 0 , not to be confused with "g", the symbol for grams ). It is used for sustained accelerations , that cause a perception of weight . For example, an object at rest on Earth's surface is subject to 1 g , equaling the conventional value of gravitational acceleration on Earth, about 9.8 m/s . More transient acceleration, accompanied with significant jerk ,
186-408: A hard disk to prevent a head crash and resulting data loss upon impact. This device is included in the many common computer and consumer electronic products that are produced by a variety of manufacturers. It is also used in some data loggers to monitor handling operations for shipping containers . The length of time in free fall is used to calculate the height of drop and to estimate the shock to
279-654: A combination may have much lower misalignment error than three discrete models combined after packaging. Micromechanical accelerometers are available in a wide variety of measuring ranges, reaching up to thousands of g ' s. The designer must compromise between sensitivity and the maximum acceleration that can be measured. Accelerometers can be used to measure vehicle acceleration. Accelerometers can be used to measure vibration on cars, machines, buildings, process control systems and safety installations. They can also be used to measure seismic activity , inclination, machine vibration, dynamic distance and speed with or without
372-650: A distance of 1 mm is subjected to a 1000 ɡ 0 deceleration. Jerk is the rate of change of acceleration. In SI units, jerk is expressed as m/s; it can also be expressed in standard gravity per second ( ɡ 0 /s; 1 ɡ 0 /s ≈ 9.81 m/s). Recent research carried out on extremophiles in Japan involved a variety of bacteria (including E. coli as a non-extremophile control) being subject to conditions of extreme gravity. The bacteria were cultivated while being rotated in an ultracentrifuge at high speeds corresponding to 403,627 g. Paracoccus denitrificans
465-506: A fluid. Many vertebrates, including humans, have these structures in their inner ears. Most invertebrates have similar organs, but not as part of their hearing organs. These are called statocysts . Mechanical accelerometers are often designed so that an electronic circuit senses a small amount of motion, then pushes on the proof mass with some type of linear motor to keep the proof mass from moving far. The motor might be an electromagnet or in very small accelerometers, electrostatic . Since
558-419: A free body (one that is free to move in space) such g-forces only arise as the "inertial" path that is the natural effect of gravitation, or the natural effect of the inertia of mass, is modified. Such modification may only arise from influences other than gravitation. Examples of important situations involving g-forces include: A classic example of negative g-force is in a fully inverted roller coaster which
651-417: A higher-g roller coaster, which in some cases exceeds this point) before losing consciousness , but through the combination of special g-suits and efforts to strain muscles—both of which act to force blood back into the brain—modern pilots can typically handle a sustained 9 g 0 (88 m/s) (see High-G training ). In aircraft particularly, vertical g-forces are often positive (force blood towards
744-413: A majority were susceptible to this attack. A number of 21st-century devices use accelerometers to align the screen depending on the direction the device is held (e.g., switching between portrait and landscape modes ). Such devices include many tablet PCs and some smartphones and digital cameras . The Amida Simputer , a handheld Linux device launched in 2004, was the first commercial handheld to have
837-406: A mechanical force, and cannot be produced by simple gravitation. Objects acted upon only by gravitation experience (or "feel") no g-force, and are weightless. g-forces, when multiplied by a mass upon which they act, are associated with a certain type of mechanical force in the correct sense of the term "force", and this force produces compressive stress and tensile stress . Such forces result in
930-410: A moving object without the need for external references. Other terms used to refer to inertial navigation systems or closely related devices include inertial guidance system, inertial reference platform, and many other variations. An accelerometer alone is unsuitable to determine changes in altitude over distances where the vertical decrease of gravity is significant, such as for aircraft and rockets. In
1023-415: A parabolic "zero-g" arc, or any free-fall in a vacuum. Another example is free-fall at a sufficiently high altitude that atmospheric effects can be neglected. However, this does not include a (non-free) fall in which air resistance produces drag forces that reduce the acceleration until constant terminal velocity is reached. At terminal velocity, the accelerometer will indicate 1 g acceleration upwards. For
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#17327879839021116-452: A range of accelerations depending on the time of exposure. This ranged from as much as 20 g 0 for less than 10 seconds, to 10 g 0 for 1 minute, and 6 g 0 for 10 minutes for both eyeballs in and out. These forces were endured with cognitive facilities intact, as subjects were able to perform simple physical and communication tasks. The tests were determined not to cause long- or short-term harm although tolerance
1209-434: A rate of change in velocity of approximately 35 km/h (22 mph) for each second that elapses. Therefore, if an automobile is capable of braking at 1 g and is traveling at 35 km/h, it can brake to a standstill in one second and the driver will experience a deceleration of 1 g . The automobile traveling at three times this speed, 105 km/h (65 mph), can brake to a standstill in three seconds. In
1302-455: A silicon micro-machined sensing element. They measure low frequencies well. Modern mechanical accelerometers are often small micro-electro-mechanical systems ( MEMS ), and are often very simple MEMS devices, consisting of little more than a cantilever beam with a proof mass (also known as seismic mass ). Damping results from the residual gas sealed in the device. As long as the Q-factor
1395-407: A small heater in a very small dome. This heats the air or other fluid inside the dome. The thermal bubble acts as the proof mass . An accompanying temperature sensor (like a thermistor ; or thermopile ) in the dome measures the temperature in one location of the dome. This measures the location of the heated bubble within the dome. When the dome is accelerated, the colder, higher density fluid pushes
1488-410: A stationary, single-axis accelerometer is oriented so that its measuring axis is horizontal, its output will be 0 g , and it will continue to be 0 g if mounted in an automobile traveling at a constant velocity on a level road. When the driver presses on the brake or gas pedal, the accelerometer will register positive or negative acceleration. If the accelerometer is rotated by 90° so that it
1581-401: A time. Specific force It is a physical quantity of kind acceleration , with dimension of length per time squared and units of metre per second squared (m·s ). It is normally applied to forces other than gravity , to emulate the relationship between gravitational acceleration and gravitational force . It can also be called mass-specific weight (weight per unit mass), as
1674-433: Is a stub . You can help Misplaced Pages by expanding it . Accelerometer An accelerometer is a device that measures the proper acceleration of an object. Proper acceleration is the acceleration (the rate of change of velocity ) of the object relative to an observer who is in free fall (that is, relative to an inertial frame of reference ). Proper acceleration is different from coordinate acceleration, which
1767-504: Is a rocket in free space: when the engines produce simple changes in velocity, those changes cause g-forces on the rocket and the passengers. The unit of measure of acceleration in the International System of Units (SI) is m/s. However, to distinguish acceleration relative to free fall from simple acceleration (rate of change of velocity), the unit g is often used. One g is the force per unit mass due to gravity at
1860-493: Is a weak effect and depends on the local density of the Earth, which is quite variable. A single-axis accelerometer measures acceleration along a specified axis. A multi-axis accelerometer detects both the magnitude and the direction of the proper acceleration, as a vector quantity, and is usually implemented as several single-axis accelerometers oriented along different axes. An accelerometer measures proper acceleration , which
1953-469: Is accelerating (changing velocity) toward the ground. In this case, the roller coaster riders are accelerated toward the ground faster than gravity would accelerate them, and are thus pinned upside down in their seats. In this case, the mechanical force exerted by the seat causes the g-force by altering the path of the passenger downward in a way that differs from gravitational acceleration. The difference in downward motion, now faster than gravity would provide,
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#17327879839022046-861: Is acceleration with respect to a given coordinate system , which may or may not be accelerating. For example, an accelerometer at rest on the surface of the Earth will measure an acceleration due to Earth's gravity straight upwards of about g ≈ 9.81 m/s . By contrast, an accelerometer that is in free fall will measure zero acceleration. Accelerometers have many uses in industry, consumer products, and science. Highly sensitive accelerometers are used in inertial navigation systems for aircraft and missiles. In unmanned aerial vehicles , accelerometers help to stabilize flight. Micromachined micro-electromechanical systems (MEMS) accelerometers are used in handheld electronic devices such as smartphones , cameras and video-game controllers to detect movement and orientation of these devices. Vibration in industrial machinery
2139-439: Is applied, the direction it acts, the location of application, and the posture of the body. The human body is flexible and deformable, particularly the softer tissues. A hard slap on the face may briefly impose hundreds of g locally but not produce any real damage; a constant 16 g for a minute, however, may be deadly. When vibration is experienced, relatively low peak g-force levels can be severely damaging if they are at
2232-469: Is called shock . When the g-force is produced by the surface of one object being pushed by the surface of another object, the reaction force to this push produces an equal and opposite force for every unit of each object's mass. The types of forces involved are transmitted through objects by interior mechanical stresses . Gravitational acceleration is one cause of an object's acceleration in relation to free fall . The g-force experienced by an object
2325-407: Is caused by the push of the seat, and it results in a g-force toward the ground. All "coordinate accelerations" (or lack of them), are described by Newton's laws of motion as follows: The Second Law of Motion , the law of acceleration, states that F = ma , meaning that a force F acting on a body is equal to the mass m of the body times its acceleration a . The Third Law of Motion ,
2418-436: Is dropped or otherwise put into a ballistic trajectory (also known as an inertial trajectory), so that it experiences "free fall", as do astronauts in orbit (astronauts experience small tidal accelerations called microgravity, which are neglected for the sake of discussion here). Some amusement park rides can provide several seconds at near-zero g. Riding NASA's " Vomit Comet " provides near-zero g-force for about 25 seconds at
2511-418: Is due to the vector sum of all gravitational and non-gravitational forces acting on an object's freedom to move. In practice, as noted, these are surface-contact forces between objects. Such forces cause stresses and strains on objects, since they must be transmitted from an object surface. Because of these strains, large g-forces may be destructive. For example, a force of 1 g on an object sitting on
2604-731: Is experienced whenever anyone rides in a vehicle because it always causes a proper acceleration, and (in the absence of gravity) also always a coordinate acceleration (where velocity changes). Whenever the vehicle changes either direction or speed, the occupants feel lateral (side to side) or longitudinal (forward and backwards) forces produced by the mechanical push of their seats. The expression "1 g = 9.806 65 m/s " means that for every second that elapses, velocity changes 9.806 65 metres per second ( 35.303 94 km/h ). This rate of change in velocity can also be denoted as 9.806 65 (metres per second) per second, or 9.806 65 m/s. For example: An acceleration of 1 g equates to
2697-413: Is in airbag deployment systems for modern automobiles. In this case, the accelerometers are used to detect the rapid negative acceleration of the vehicle to determine when a collision has occurred and the severity of the collision. Another common automotive use is in electronic stability control systems, which use a lateral accelerometer to measure cornering forces. The widespread use of accelerometers in
2790-410: Is monitored by accelerometers. Seismometers are sensitive accelerometers for monitoring ground movement such as earthquakes. When two or more accelerometers are coordinated with one another, they can measure differences in proper acceleration, particularly gravity, over their separation in space—that is, the gradient of the gravitational field . Gravity gradiometry is useful because absolute gravity
2883-399: Is not the force that produces the acceleration, but rather the equal-and-opposite reaction force to it. If the direction upward is taken as positive (the normal cartesian convention) then positive g-force (an acceleration vector that points upward) produces a force/weight on any mass, that acts downward (an example is positive-g acceleration of a rocket launch, producing downward weight). In
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2976-425: Is not too low, damping does not result in a lower sensitivity. Under the influence of external accelerations, the proof mass deflects from its neutral position. This deflection is measured in an analog or digital manner. Most commonly, the capacitance between a set of fixed beams and a set of beams attached to the proof mass is measured. This method is simple, reliable, and inexpensive. Integrating piezoresistors in
3069-422: Is sometimes referred to as red out where vision is literally reddened due to the blood-laden lower eyelid being pulled into the field of vision. Negative g-force is generally unpleasant and can cause damage. Blood vessels in the eyes or brain may swell or burst under the increased blood pressure, resulting in degraded sight or even blindness. The human body is better at surviving g-forces that are perpendicular to
3162-433: Is technically incorrect as it is a measure of acceleration , not force. While acceleration is a vector quantity, g-force accelerations ("g-forces" for short) are often expressed as a scalar , based on the vector magnitude, with positive g-forces pointing downward (indicating upward acceleration), and negative g-forces pointing upward. Thus, a g-force is a vector of acceleration. It is an acceleration that must be produced by
3255-439: Is the acceleration it experiences relative to freefall and is the acceleration felt by people and objects. Put another way, at any point in spacetime the equivalence principle guarantees the existence of a local inertial frame , and an accelerometer measures the acceleration relative to that frame. Such accelerations are popularly denoted g-force ; i.e., in comparison to standard gravity . An accelerometer at rest relative to
3348-462: Is the acceleration relative to free-fall, not the "standard" acceleration that is relative to a coordinate system. In open channel hydraulics , specific force ( F s {\displaystyle F_{s}} ) has a different meaning: where Q is the discharge, g is the acceleration due to gravity, A is the cross-sectional area of flow, and z is the depth of the centroid of flow area A. This classical mechanics –related article
3441-543: Is the standard symbol for the gravitational constant . This notation is commonly used in aviation, especially in aerobatic or combat military aviation, to describe the increased forces that must be overcome by pilots in order to remain conscious and not g-LOC ( g -induced loss of consciousness). Measurement of g-force is typically achieved using an accelerometer (see discussion below in section #Measurement using an accelerometer ). In certain cases, g-forces may be measured using suitably calibrated scales. The term g-"force"
3534-531: Is vertical, it will read +1 g upwards even though stationary. In that situation, the accelerometer is subject to two forces: the gravitational force and the ground reaction force of the surface it is resting on. Only the latter force can be measured by the accelerometer, due to mechanical interaction between the accelerometer and the ground. The reading is the acceleration the instrument would have if it were exclusively subject to that force. A three-axis accelerometer will output zero‑g on all three axes if it
3627-527: Is zero for freely-falling objects, since gravity acting alone does not produce g-forces or specific forces. Accelerometers on the surface of the Earth measure a constant 9.8 m/s^2 even when they are not accelerating (that is, when they do not undergo coordinate acceleration). This is because accelerometers measure the proper acceleration produced by the g-force exerted by the ground (gravity acting alone never produces g-force or specific force). Accelerometers measure specific force (proper acceleration), which
3720-781: The Nintendo 3DS system. Sleep phase alarm clocks use accelerometric sensors to detect movement of a sleeper, so that it can wake the person when he/she is not in REM phase, in order to awaken the person more easily. A microphone or eardrum is a membrane that responds to oscillations in air pressure. These oscillations cause acceleration, so accelerometers can be used to record sound. A 2012 study found that voices can be detected by smartphone accelerometers in 93% of typical daily situations. Conversely, carefully designed sounds can cause accelerometers to report false data. One study tested 20 models of (MEMS) smartphone accelerometers and found that
3813-483: The nematodes Panagrolaimus superbus and Caenorhabditis elegans were shown to be able to tolerate 400,000 × g for 1 hour. The research has implications on the feasibility of panspermia . An accelerometer , in its simplest form, is a damped mass on the end of a spring, with some way of measuring how far the mass has moved on the spring in a particular direction, called an 'axis'. Accelerometers are often calibrated to measure g-force along one or more axes. If
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3906-422: The resonant frequency of organs or connective tissues. To some degree, g-tolerance can be trainable, and there is also considerable variation in innate ability between individuals. In addition, some illnesses, particularly cardiovascular problems, reduce g-tolerance. Aircraft pilots (in particular) sustain g-forces along the axis aligned with the spine. This causes significant variation in blood pressure along
3999-448: The weight of an object is equal to the magnitude of the gravity force acting on it. The g-force is an instance of specific force measured in units of the standard gravity ( g ) instead of m/s², i.e., in multiples of g (e.g., "3 g "). The (mass-)specific force is not a coordinate acceleration , but rather a proper acceleration , which is the acceleration relative to free-fall. Forces, specific forces, and proper accelerations are
4092-431: The 1.0 g upward proper acceleration on the pilot, even though this velocity in the upward direction does not change (this is similar to the situation of a person standing on the ground, where the ground provides this force and this g-force). If the pilot were suddenly to pull back on the stick and make his plane accelerate upwards at 9.8 m/s, the total g‑force on his body is 2 g , half of which comes from
4185-688: The 4th generation. Along with orientation view adjustment, accelerometers in mobile devices can also be used as pedometers , in conjunction with specialized applications . Automatic Collision Notification (ACN) systems also use accelerometers in a system to call for help in event of a vehicle crash. Prominent ACN systems include OnStar AACN service, Ford Link's 911 Assist , Toyota's Safety Connect , Lexus Link , or BMW Assist . Many accelerometer-equipped smartphones also have ACN software available for download. ACN systems are activated by detecting crash-strength accelerations. Accelerometers are used in vehicle Electronic stability control systems to measure
4278-439: The Earth's center (in vacuum), or (to good approximation) inside a spacecraft in Earth orbit . These are examples of coordinate acceleration (a change in velocity) without a sensation of weight. In the absence of gravitational fields, or in directions at right angles to them, proper and coordinate accelerations are the same, and any coordinate acceleration must be produced by a corresponding g-force acceleration. An example of this
4371-556: The Earth's surface and is the standard gravity (symbol: g n ), defined as 9.806 65 metres per second squared , or equivalently 9.806 65 newtons of force per kilogram of mass. The unit definition does not vary with location—the g-force when standing on the Moon is almost exactly 1 ⁄ 6 that on Earth. The unit g is not one of the SI units, which uses "g" for gram. Also, " g " should not be confused with " G ", which
4464-410: The Earth's surface is caused by the mechanical force exerted in the upward direction by the ground , keeping the object from going into free fall. The upward contact force from the ground ensures that an object at rest on the Earth's surface is accelerating relative to the free-fall condition. (Free fall is the path that the object would follow when falling freely toward the Earth's center). Stress inside
4557-435: The Earth's surface will indicate approximately 1 g upwards because the Earth's surface exerts a normal force upwards relative to the local inertial frame (the frame of a freely falling object near the surface). To obtain the acceleration due to motion with respect to the Earth, this "gravity offset" must be subtracted and corrections made for effects caused by the Earth's rotation relative to the inertial frame. The reason for
4650-565: The acceleration of gravity, and more than 25 g 0 for 1.1 seconds, proving that the human body is capable of this. Stapp lived another 45 years to age 89 without any ill effects. The highest recorded g-force experienced by a human who survived was during the 2003 IndyCar Series finale at Texas Motor Speedway on 12 October 2003, in the 2003 Chevy 500 when the car driven by Kenny Bräck made wheel-to-wheel contact with Tomas Scheckter 's car. This immediately resulted in Bräck's car impacting
4743-439: The acceleration of objects with respect to the Earth, such as for use in an inertial navigation system , a knowledge of local gravity is required. This can be obtained either by calibrating the device at rest, or from a known model of gravity at the approximate current position. A basic mechanical accelerometer is a damped proof mass on a spring . When the accelerometer experiences an acceleration, Newton's third law causes
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#17327879839024836-522: The appearance of a gravitational offset is Einstein's equivalence principle , which states that the effects of gravity on an object are indistinguishable from acceleration. When held fixed in a gravitational field by, for example, applying a ground reaction force or an equivalent upward thrust, the reference frame for an accelerometer (its own casing) accelerates upwards with respect to a free-falling reference frame. The effects of this acceleration are indistinguishable from any other acceleration experienced by
4929-412: The area, is again the related mechanical force, which is the product of the g-force and the mass hanging below the point of mechanical support. The mechanical resistive force spreads from points of contact with the floor or supporting structure, and gradually decreases toward zero at the unsupported ends (the top in the case of support from below, such as a seat or the floor, the bottom for a hanging part of
5022-438: The automotive industry has pushed their cost down dramatically. Another automotive application is the monitoring of noise, vibration, and harshness (NVH), conditions that cause discomfort for drivers and passengers and may also be indicators of mechanical faults. Tilting trains use accelerometers and gyroscopes to calculate the required tilt. Modern electronic accelerometers are used in remote sensing devices intended for
5115-403: The body or object). With compressive force counted as negative tensile force, the rate of change of the tensile force in the direction of the g-force, per unit mass (the change between parts of the object such that the slice of the object between them has unit mass), is equal to the g-force plus the non-gravitational external forces on the slice, if any (counted positive in the direction opposite to
5208-410: The case of an increase in speed from 0 to v with constant acceleration within a distance of s this acceleration is v /(2 s ). Preparing an object for g-tolerance (not getting damaged when subjected to a high g-force) is called g-hardening. This may apply to, e.g., instruments in a projectile shot by a gun. Human tolerances depend on the magnitude of the gravitational force, the length of time it
5301-440: The catch fence that would record a peak of 214 g 0 . Impact and mechanical shock are usually used to describe a high- kinetic-energy , short-term excitation. A shock pulse is often measured by its peak acceleration in ɡ 0 ·s and the pulse duration. Vibration is a periodic oscillation which can also be measured in ɡ 0 ·s as well as frequency. The dynamics of these phenomena are what distinguish them from
5394-732: The circuit's electronic behavior can be carefully designed, and the proof mass does not move far, these designs can be very stable (i.e. they do not oscillate ), very linear with a controlled frequency response. (This is called servo mode design.) In mechanical accelerometers, measurement is often electrical, piezoelectric , piezoresistive or capacitive . Piezoelectric accelerometers use piezoceramic sensors (e.g. lead zirconate titanate ) or single crystals (e.g. quartz , tourmaline ). They are unmatched in high frequency measurements, low packaged weight, and resistance to high temperatures. Piezoresistive accelerometers resist shock (very high accelerations) better. Capacitive accelerometers typically use
5487-409: The damping causes accelerometers to have a frequency response . Many animals have sensory organs to detect acceleration, especially gravity. In these, the proof mass is usually one or more crystals of calcium carbonate otoliths (Latin for "ear stone") or statoconia , acting against a bed of hairs connected to neurons. The hairs form the springs, with the neurons as sensors. The damping is usually by
5580-409: The feet and away from the head); this causes problems with the eyes and brain in particular. As positive vertical g-force is progressively increased (such as in a centrifuge ) the following symptoms may be experienced: Resistance to "negative" or "downward" g, which drives blood to the head, is much lower. This limit is typically in the −2 to −3 g 0 (−20 to −29 m/s) range. This condition
5673-429: The floor of an elevator to a standing person, most of the body experiences compressive stress which at any height, if multiplied by the area, is the related mechanical force, which is the product of the g-force and the supported mass (the mass above the level of support, including arms hanging down from above that level). At the same time, the arms themselves experience a tensile stress, which at any height, if multiplied by
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#17327879839025766-436: The g-force). For a given g-force the stresses are the same, regardless of whether this g-force is caused by mechanical resistance to gravity, or by a coordinate-acceleration (change in velocity) caused by a mechanical force, or by a combination of these. Hence, for people all mechanical forces feels exactly the same whether they cause coordinate acceleration or not. For objects likewise, the question of whether they can withstand
5859-445: The g-forces caused by a relatively longer-term accelerations. After a free fall from a height h {\displaystyle h} followed by deceleration over a distance d {\displaystyle d} during an impact, the shock on an object is ( h / d ) {\displaystyle (h/d)} · ɡ 0 . For example, a stiff and compact object dropped from 1 m that impacts over
5952-408: The hand holding the rock, the pilot as the rock. When flying straight and level at 1 g , the pilot is acted upon by the force of gravity. His weight (a downward force) is 725 newtons (163 lb f ). In accordance with Newton's third law, the plane and the seat underneath the pilot provides an equal and opposite force pushing upwards with a force of 725 N. This mechanical force provides
6045-445: The heated bubble. The measured temperature changes. The temperature measurement is interpreted as acceleration. The fluid provides the damping. Gravity acting on the fluid provides the spring. Since the proof mass is very lightweight gas, and not held by a beam or lever, thermal accelerometers can survive high shocks . Another variation uses a wire to both heat the gas and detect the change in temperature. The change of temperature changes
6138-428: The impact of head collisions. Accelerometers have been used to calculate gait parameters , such as stance and swing phase. This kind of sensor can be used to measure or monitor people. An inertial navigation system is a navigation aid that uses a computer and motion sensors (accelerometers) to continuously calculate via dead reckoning the position, orientation, and velocity (direction and speed of movement) of
6231-471: The influence of gravity. Applications for accelerometers that measure gravity, wherein an accelerometer is specifically configured for use in gravimetry , are called gravimeters . Accelerometers are also increasingly used in the biological sciences. High frequency recordings of bi-axial or tri-axial acceleration allows the discrimination of behavioral patterns while animals are out of sight. Furthermore, recordings of acceleration allow researchers to quantify
6324-420: The instrument so that an accelerometer cannot detect the difference between sitting in a rocket on the launch pad, and being in the same rocket in deep space while it uses its engines to accelerate at 1 g. For similar reasons, an accelerometer will read zero during any type of free fall . This includes use in a coasting spaceship in deep space far from any mass, a spaceship orbiting the Earth, an airplane in
6417-543: The last several years, several companies have produced and marketed sports watches for runners that include footpods , containing accelerometers to help determine the speed and distance for the runner wearing the unit. In Belgium, accelerometer-based step counters are promoted by the government to encourage people to walk a few thousand steps each day. Herman Digital Trainer uses accelerometers to measure strike force in physical training. It has been suggested to build football helmets with accelerometers in order to measure
6510-425: The law of reciprocal actions, states that all forces occur in pairs, and these two forces are equal in magnitude and opposite in direction. Newton's third law of motion means that not only does gravity behave as a force acting downwards on, say, a rock held in your hand but also that the rock exerts a force on the Earth, equal in magnitude and opposite in direction. In an airplane, the pilot's seat can be thought of as
6603-471: The length of the subject's body, which limits the maximum g-forces that can be tolerated. Positive, or "upward" g-force, drives blood downward to the feet of a seated or standing person (more naturally, the feet and body may be seen as being driven by the upward force of the floor and seat, upward around the blood). Resistance to positive g-force varies. A typical person can handle about 5 g 0 (49 m/s) (meaning some people might pass out when riding
6696-399: The mechanical g-force without damage is the same for any type of g-force. For example, upward acceleration (e.g., increase of speed when going up or decrease of speed when going down) on Earth feels the same as being stationary on a celestial body with a higher surface gravity . Gravitation acting alone does not produce any g-force; g-force is only produced from mechanical pushes and pulls. For
6789-399: The monitoring of active volcanoes to detect the motion of magma . Accelerometers are increasingly being incorporated into personal electronic devices to detect the orientation of the device, for example, a display screen. A free-fall sensor (FFS) is an accelerometer used to detect if a system has been dropped and is falling. It can then apply safety measures such as parking the head of
6882-498: The number of steps taken and distance traveled than a mechanical sensor can provide. Nintendo's Wii video game console uses a controller called a Wii Remote that contains a three-axis accelerometer and was designed primarily for motion input. Users also have the option of buying an additional motion-sensitive attachment, the Nunchuk , so that motion input could be recorded from both of the user's hands independently. Is also used on
6975-480: The object is ensured from the fact that the ground contact forces are transmitted only from the point of contact with the ground. Objects allowed to free-fall in an inertial trajectory , under the influence of gravitation only, feel no g-force – a condition known as weightlessness . Being in free fall in an inertial trajectory is colloquially called "zero- g ", which is short for "zero g-force". Zero g-force conditions would occur inside an elevator falling freely toward
7068-430: The operational sensation of weight, but the equation carries a sign change due to the definition of positive weight in the direction downward, so the direction of weight-force is opposite to the direction of g-force acceleration: The reason for the minus sign is that the actual force (i.e., measured weight) on an object produced by a g-force is in the opposite direction to the sign of the g-force, since in physics, weight
7161-416: The package. Some smartphones , digital audio players and personal digital assistants contain accelerometers for user interface control; often the accelerometer is used to present landscape or portrait views of the device's screen, based on the way the device is being held. Apple has included an accelerometer in every generation of iPhone , iPad , and iPod touch , as well as in every iPod nano since
7254-487: The presence of a gravitational gradient, the calibration and data reduction process is numerically unstable. Accelerometers are used to detect apogee in both professional and in amateur rocketry. Accelerometers are also being used in Intelligent Compaction rollers. Accelerometers are used alongside gyroscopes in inertial navigation systems. One of the most common uses for MEMS accelerometers
7347-803: The rate at which an animal is expending energy in the wild, by either determination of limb-stroke frequency or measures such as overall dynamic body acceleration Such approaches have mostly been adopted by marine scientists due to an inability to study animals in the wild using visual observations, however an increasing number of terrestrial biologists are adopting similar approaches. For example, accelerometers have been used to study flight energy expenditure of Harris's Hawk ( Parabuteo unicinctus ). Researchers are also using smartphone accelerometers to collect and extract mechano-biological descriptors of resistance exercise. Increasingly, researchers are deploying accelerometers with additional technology, such as cameras or microphones, to better understand animal behaviour in
7440-465: The resistance of the wire. A two dimensional accelerometer can be economically constructed with one dome, one bubble and two measurement devices. Most micromechanical accelerometers operate in-plane , that is, they are designed to be sensitive only to a direction in the plane of the die . By integrating two devices perpendicularly on a single die a two-axis accelerometer can be made. By adding another out-of-plane device, three axes can be measured. Such
7533-496: The safety and viability of a structure. This type of monitoring is called Health Monitoring, which usually involves other types of instruments, such as displacement sensors -Potentiometers, LVDTs, etc.- deformation sensors -Strain Gauges, Extensometers-, load sensors -Load Cells, Piezo-Electric Sensors- among others. Zoll's AED Plus uses CPR-D•padz which contain an accelerometer to measure the depth of CPR chest compressions. Within
7626-434: The same in all reference frames, but coordinate accelerations are frame-dependent. For free bodies, the specific force is the cause of, and a measure of, the body's proper acceleration. The acceleration of an object free falling towards the earth depends on the reference frame (it disappears in the free-fall frame, also called the inertial frame), but any g-force "acceleration" will be present in all frames. This specific force
7719-468: The same reason a skydiver , upon reaching terminal velocity, does not feel as though he or she were in "free-fall", but rather experiences a feeling similar to being supported (at 1 g) on a "bed" of uprushing air. Acceleration is quantified in the SI unit metres per second per second (m/s ), in the cgs unit gal (Gal), or popularly in terms of standard gravity ( g ). For the practical purpose of finding
7812-438: The same way, a negative-g force is an acceleration vector downward (the negative direction on the y axis), and this acceleration downward produces a weight-force in a direction upward (thus pulling a pilot upward out of the seat, and forcing blood toward the head of a normally oriented pilot). If a g-force (acceleration) is vertically upward and is applied by the ground (which is accelerating through space-time) or applied by
7905-538: The seat pushing the pilot to resist gravity, and half from the seat pushing the pilot to cause his upward acceleration—a change in velocity which also is a proper acceleration because it also differs from a free fall trajectory. Considered in the frame of reference of the plane his body is now generating a force of 1,450 N (330 lb f ) downwards into his seat and the seat is simultaneously pushing upwards with an equal force of 1450 N. Unopposed acceleration due to mechanical forces, and consequentially g-force,
7998-399: The spine. In general when the acceleration is forwards (subject essentially lying on their back, colloquially known as "eyeballs in"), a much higher tolerance is shown than when the acceleration is backwards (lying on their front, "eyeballs out") since blood vessels in the retina appear more sensitive in the latter direction. Early experiments showed that untrained humans were able to tolerate
8091-457: The spring's compression to adjust to exert an equivalent force on the mass to counteract the acceleration. Since the spring's force scales linearly with amount of compression (according to Hooke's law ) and because the spring constant and mass are known constants, a measurement of the spring's compression is also a measurement of acceleration. The system is damped to prevent oscillations of the mass and spring interfering with measurements. However,
8184-445: The springs to detect spring deformation, and thus deflection, is a good alternative, although a few more process steps are needed during the fabrication sequence. For very high sensitivities quantum tunnelling is also used; this requires a dedicated process making it very expensive. Optical measurement has been demonstrated in laboratory devices. Another MEMS-based accelerometer is a thermal (or convective ) accelerometer. It contains
8277-408: The user to monitor machines and detect these faults before the rotating equipment fails completely. Accelerometers are used to measure the motion and vibration of a structure that is exposed to dynamic loads. Dynamic loads originate from a variety of sources including: Under structural applications, measuring and recording how a structure dynamically responds to these inputs is critical for assessing
8370-439: The vehicle's actual movement. A computer compares the vehicle's actual movement to the driver's steering and throttle input. The stability control computer can selectively brake individual wheels and/or reduce engine power to minimize the difference between driver input and the vehicle's actual movement. This can help prevent the vehicle from spinning or rolling over. Some pedometers use an accelerometer to more accurately measure
8463-399: The wild (for example, hunting behaviour of Canada lynx ). Accelerometers are also used for machinery health monitoring to report the vibration and its changes in time of shafts at the bearings of rotating equipment such as turbines, pumps , fans, rollers, compressors , or bearing fault which, if not attended to promptly, can lead to costly repairs. Accelerometer vibration data allows
8556-411: Was one of the bacteria that displayed not only survival but also robust cellular growth under these conditions of hyperacceleration, which are usually only to be found in cosmic environments, such as on very massive stars or in the shock waves of supernovas . Analysis showed that the small size of prokaryotic cells is essential for successful growth under hypergravity . Notably, two multicellular species,
8649-424: Was quite subjective, with only the most motivated non-pilots capable of completing tests. The record for peak experimental horizontal g-force tolerance is held by acceleration pioneer John Stapp , in a series of rocket sled deceleration experiments culminating in a late 1954 test in which he was clocked in a little over a second from a land speed of Mach 0.9. He survived a peak "eyeballs-out" acceleration of 46.2 times
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