In the physical sciences, mass and weight are different properties. Mass is an inertial property; that is, the tendency of an object to remain at constant velocity unless acted upon by an external force. Weight is the force created when a mass is acted upon by a gravitational field. A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... For other uses, see Mass (disambiguation). ... For other uses, see Weight (disambiguation). ... This article is about inertia as it applies to local motion. ... For other uses, see Force (disambiguation). ... Gravity redirects here. ...

While the weight of matter is entirely dependent upon the strength of local gravity, the mass of matter is constant (assuming it is not traveling at a relativistic speed with respect to an observer). Accordingly, for astronauts in microgravity, no effort is required to hold objects off the cabin floor since such objects naturally hover; they are “weightless.” However, since objects in microgravity still retain their mass, an astronaut must exert one hundred times more force to accelerate a 100-kilogram object at the same rate as a 1-kilogram object. For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... Kg redirects here. ...

Overview

Matter’s mass strongly influences many familiar kinetic properties.

Mass is an inertial property. Inertia is sensed when a bowling ball is pushed horizontally on a level, smooth surface. This is quite distinct from “weight,” which is the downwards gravitational force of the bowling ball that one must counter when holding it off the floor. Unless relativistic effects apply, mass is an unchanging, universal property of matter that is unaffected by gravity. Weight on the other hand, is a property of matter that is entirely dependent upon the local strength of gravity. For instance, an astronaut’s weight on the Moon is one-sixth of that on the Earth, whereas his mass has changed little during the trip. Consequently, wherever the physics of recoil kinetics (mass, velocity, inertia, inelastic and elastic collisions) dominate and the influence of gravity is a negligible factor, the behavior of objects remains consistent even where gravity is relatively weak. For instance, billiard balls on a billiards table would scatter and recoil with the same speeds and energies after a break shot on the Moon as on Earth; they would however, drop into the pockets much more slowly. Image File history File linksMetadata Size of this preview: 800 × 533 pixelsFull resolution (2310 × 1540 pixel, file size: 1. ... Image File history File linksMetadata Size of this preview: 800 × 533 pixelsFull resolution (2310 × 1540 pixel, file size: 1. ... This article is about inertia as it applies to local motion. ... A ten-pin bowling ball and two pins A bowling ball is a round ball made from rubber, urethane, plastic, reactive resin (solid, particle, or pearl) or a combination of these materials which is used in the sport of bowling. ... An inelastic collision is a collision in which some of the kinetic energy of the colliding bodies is converted into internal energy in at least one body such that kinetic energy is not conserved. ... As long as black-body radiation (not shown) doesn’t escape a system, atoms in thermal agitation undergo essentially elastic collisions. ...

In the physical sciences, the terms “mass” and “weight” are rigidly defined as separate measures in order to enforce clarity and precision. In everyday use, given that all masses on Earth have weight and this relationship is usually highly proportional,^[1] “weight” often serves to describe both properties, its meaning being dependent upon context. For example, in commerce, the “net weight” of retail products actually refers to mass and is properly expressed in pounds (U.S.) or kilograms (see also Pound: Use in commerce). Conversely, the “load index” rating on automobile tires, which specifies the maximum structural load for a tire in kilograms, refers to weight; that is, the force due to gravity. The pound or pound-mass (abbreviations: lb, , lbm, or sometimes in the United States: #) is a unit of mass (sometimes called weight in everyday parlance) in a number of different systems, including the imperial and US and older English systems. ... Automobile tires are described by an alphanumeric code which is generally molded into the side-wall of the tire. ... This article or section does not adequately cite its references or sources. ...

Because mass and weight are separate quantities, they have different units of measure. In the International System of Units (SI), the kilogram is the unit of mass, and the newton is the unit of force. The non-SI kilogram-force is also a unit of force typically used in the measure of weight. Similarly, the avoirdupois pound, used in both the Imperial system and U.S. customary units, is a unit of mass and its related unit of force is the pound-force. An object with a mass of one kilogram will accelerate at one meter per second squared (about one-tenth the acceleration due to Earth’s gravity) when acted upon by a force of one newton. “SI” redirects here. ... Kg redirects here. ... For other uses, see Newton (disambiguation). ... The unit kilogram-force (kgf, often just kg) or kilopond (kp) is defined as the force exerted by one kilogram of mass in standard Earth gravity. ... The avoirdupois (IPA: ; French IPA: ) system is a system of weights (or, properly, mass) based on a pound of sixteen ounces. ... The pound or pound-mass (abbreviations: lb, , lbm, or sometimes in the United States: #) is a unit of mass (sometimes called weight in everyday parlance) in a number of different systems, including the imperial and US and older English systems. ... This article is about post-1824 Imperial units, please see also English unit, U.S. customary unit or Avoirdupois. ... U.S. customary units, also known in the United States as English units[1] (but see English unit) or standard units, are units of measurement that are currently used in the USA, in some cases alongside units from SI (the International System of Units — the modern metric system). ... The pound-force is a non-SI unit of force or weight (properly abbreviated lbf or lbf). The pound-force is equal to a mass of one pound multiplied by the standard acceleration due to gravity on Earth (which is defined as exactly 9. ... Acceleration is the time rate of change of velocity and/or direction, and at any point on a velocity-time graph, it is given by the slope of the tangent to the curve at that point. ... The metre (or meter) per second squared is the SI derived unit of acceleration. ...

Converting units of mass to equivalent forces on Earth

Gravity anomalies covering the Southern Ocean are shown here in false-color relief. This image has been normalized to remove variation due to differences in latitude.

When an object’s weight (its gravitational force) is expressed in kilograms, the unit of measure is not a true kilogram; it is the kilogram-force (kgf or kg-f), also known as the kilopond (kp), which is a non-SI unit of force. All objects on Earth are subject to a gravitational acceleration of approximately 9.8 m/s². The CGPM (also known as the “General Conference on Weights and Measures”) fixed the value of standard gravity at precisely 9.80665 m/s² so that disciplines such as metrology would have a standard value for converting units of defined mass into defined forces and pressures. In fact, the kilogram-force is defined as precisely 9.80665 newtons. As a practical matter, gravitational acceleration (symbol: g) varies slightly with latitude, elevation and subsurface density; these variations are typically only a few tenths of a percent. See also Gravimetry. Image File history File links Download high-resolution version (1155x806, 1211 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Gravitation ... Image File history File links Download high-resolution version (1155x806, 1211 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Gravitation ... The unit kilogram-force (kgf, often just kg) or kilopond (kp) is defined as the force exerted by one kilogram of mass in standard Earth gravity. ... The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures (CGPM, never GCWM). ... g (also gee, g-force or g-load) is a non-SI unit of acceleration defined as exactly 9. ... Metrology (from Greek metron (measure), and -logy) is the science of measurement. ... This article is about pressure in the physical sciences. ... This article is about the geographical term. ... Elevation histogram of the surface of the Earth – approximately 71% of the Earths surface is covered with water. ... Gravimetry is the measurement of a gravitational field. ...

Professionals in engineering and scientific disciplines involving accelerations and kinetic energies rigorously maintain the distinctions between mass, force, and weight, as well as their respective units of measure. Engineers in disciplines involving weight loading (force on a structure due to gravity), such as structural engineering, first convert loads due to objects like concrete and automobiles—which are always tallied in kilograms—to newtons before continuing with their calculations. Primarily, this is because material properties like elastic modulus are measured and published in terms of the newton and pascal (a unit of pressure derived from the newton). For all practical engineering purposes on Earth, mass in kilograms is converted to weight in newtons by multiplying by 9.80665 (standard gravity). The cars of a roller coaster reach their maximum kinetic energy when at the bottom of their path. ... For other uses, see Weight (disambiguation). ... This article or section does not adequately cite its references or sources. ... Taipei 101, the worlds tallest building as of 2004. ... An elastic modulus, or modulus of elasticity, is the mathematical description of an object or substances tendency to be deformed when a force is applied to it. ... For other uses, see Pascal. ...

Buoyancy and “conventional mass”

Regardless of the fluid in which an object is immersed (gas or liquid), the buoyancy of an object is proportional to the mass of the fluid it displaces.

The masses of objects are relatively invariant whereas their weights vary slightly with changes in barometric pressure, such as with changes in weather and altitude. This is because objects have volume and therefore have a buoyant effect in air. Buoyancy—a force that opposes gravity—reduces the weight of all objects immersed in fluids. This means that objects with precisely the same mass but with different densities displace different volumes and therefore have different buoyancies and weights. Image File history File links Submerged-and-Displacing. ... Image File history File links Submerged-and-Displacing. ... For other uses, see Volume (disambiguation). ... In physics, buoyancy is the upward force on an object produced by the surrounding fluid (i. ... A fluid is defined as a substance that continually deforms (flows) under an applied shear stress regardless of the magnitude of the applied stress. ... For other uses, see Density (disambiguation). ...

Normally, the effect of air buoyancy is too small to be of any consequence in normal day-to-day activities. For instance, buoyancy’s diminishing effect upon one’s body weight (a relatively low-density object) is 1/860 that of gravity and variations in barometric pressure rarely affect one’s weight more than ±1 part in 30,000.^[2] In metrology however, mass standards are calibrated with extreme accuracy, so air density must be taken into account to allow for buoyancy effects. Metrology (from Greek metron (measure), and -logy) is the science of measurement. ...

Given the extremely high cost of platinum-iridium mass standards like the International Prototype Kilogram (IPK), high-quality “working” standards are made of special stainless steel alloys that occupy greater volume than those made of platinum-iridium, which have a density of about 21,550 kg/m³. For convenience, a standard value of buoyancy relative to stainless steel was developed for metrology work and this results in the term “conventional mass.”^[3] Conventional mass is defined as follows: “For a mass at 20 °C, ‘conventional mass’ is the mass of a reference standard of density 8000 kg/m³ which it balances in air with a density of 1.2 kg/m³.” The effect is a small one, 150 ppm for stainless steel mass standards, but the appropriate corrections are made during the calibration of all precision mass standards so that they have the true mass indicated on them. In routine laboratory use however, the reading on a precision scale when a stainless steel standard is placed upon it is actually its conventional mass; that is, its true mass minus buoyancy. Also, any object compared to a stainless steel mass standard has its conventional mass measured; that is, its true mass minus some (usually unknown) degree of buoyancy. General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Standard atomic weight 195. ... This article is about the chemical element. ... Kg redirects here. ... The 630 foot (192 m) high, stainless-clad (type 304) Gateway Arch defines St. ... The parts-per notations are used to denote low concentrations of chemical elements. ...

Types of scales and what they measure

A balance-type weighing scale: Unaffected by the strength of gravity

Load-cell based bathroom scale: Affected by the strength of gravity

Technically, whenever someone stands on a balance-beam-type scale at a doctor’s office, they are truly having their mass measured. This is because balances (“dual-pan” mass comparators) compare the weight of the mass on the platform with that of the sliding counterweights on the beams; gravity serves only as the force-generating mechanism that allows the needle to diverge from the “balanced” (null) point. Balances can be used on the Moon with no change in the reading. Conversely, whenever someone steps onto spring-based or digital load cell-based scales (single-pan devices), they are technically having their weight (force due to strength of gravity) measured. On force-measuring instruments such as these, variations in the strength of gravity affect the reading. As a practical matter, when force-measuring scales are used in commerce or hospitals, they are calibrated on-site and certified on that basis so the measure is mass, expressed in kilograms, to the desired level of accuracy.^[4] Image File history File links Size of this preview: 800 × 574 pixel Image in higher resolution (1932 × 1387 pixel, file size: 198 KB, MIME type: image/jpeg) Photo of a four-beam mechanical balance scale. ... Image File history File links Size of this preview: 800 × 574 pixel Image in higher resolution (1932 × 1387 pixel, file size: 198 KB, MIME type: image/jpeg) Photo of a four-beam mechanical balance scale. ... Image File history File linksMetadata No higher resolution available. ... Image File history File linksMetadata No higher resolution available. ... Digital kitchen scales. ... Digital kitchen scales. ... A single-point load cell A load cell is typically an electronic device (transducer) that is used to convert a force into an electrical signal. ...

See also

An objects weight, henceforth called actual weight, is the downward force exerted upon it by the earths gravity. ... Gravimetry is the measurement of a gravitational field. ... This article is about inertia as it applies to local motion. ... “SI” redirects here. ... Kg redirects here. ... The unit kilogram-force (kgf, often just kg) or kilopond (kp) is defined as the force exerted by one kilogram of mass in standard Earth gravity. ... For other uses, see Mass (disambiguation). ... For other uses, see Newton (disambiguation). ... The pound or pound-mass (abbreviations: lb, , lbm, or sometimes in the United States: #) is a unit of mass (sometimes called weight in everyday parlance) in a number of different systems, including the imperial and US and older English systems. ... The pound-force is a non-SI unit of force or weight (properly abbreviated lbf or lbf). The pound-force is equal to a mass of one pound multiplied by the standard acceleration due to gravity on Earth (which is defined as exactly 9. ... g (also gee, g-force or g-load) is a non-SI unit of acceleration defined as exactly 9. ... For other uses, see Weight (disambiguation). ...

Notes

1. ^ On Earth, masses with densities less than that of air float and have negative weight; that is, they are buoyant. Such masses have positive weight in a vacuum.
2. ^ Assumptions: An air density of 1160 g/m³, an average density of a human body (with collapsed lungs) equal to that of water, and variations in barometric pressure rarely exceeding ±22 torr. Assumptions primary variables: An altitude of 194 meters above mean sea level (the worldwide median altitude of human habitation), an indoor temperature of 23 °C, a dewpoint of 9 °C, and 760 mmHg sea level–corrected barometric pressure.
3. ^ International Recommendation OIML R33, International Organization of Legal Metrology.
4. ^ National General Conference on Weights and Measures, Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices, NIST Handbook 44

In physics, buoyancy is the upward force on an object produced by the surrounding fluid (i. ... The International Organization of Legal Metrology or Organization Internationale de Métrologie Légale (OIML) is an intergovernmental treaty organization. ...

External links

• NPL: What are the differences between mass, weight, force and load?