In the physical sciences, weight is a measurement of the gravitational force acting on an object. A spring scale is a Weighing scale used to measure Force, such as the force of Gravity, exerted on a Mass or the force of a person's grip Physical science is an encompassing term for the branches of Natural science and Science that study non-living systems in contrast to the biological sciences Measurement is the process of estimating the magnitude of some attribute of an object such as its length or weight relative to some standard ( unit of measurement) such as In Physics, a force is whatever can cause an object with Mass to Accelerate. ^[1] Near the surface of the Earth, the acceleration due to gravity is approximately constant; this means that an object's weight is roughly proportional to its mass. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 Earth's gravity, denoted by g, refers to the Gravitational attraction that the Earth exerts on objects on or near its surface Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object

In commerce and in many other applications, weight means the same as mass as that term is used in physics. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object ^[1][2]

Contents 1 Weight and mass 2 Units of weight 2.1 SI units 2.2 The pound and other non-SI units 2.3 Conversion between weight (force) and mass 3 Sensation of weight 4 Measuring weight 5 Relative weights on the Earth, other planets and the Moon 6 References 7 See also

Weight and mass

Main article: Mass versus weight

In modern scientific usage, weight and mass are fundamentally different quantities: mass is an intrinsic property of matter, whereas weight is a force that results from the action of gravity on matter: it measures how strongly gravity pulls on that matter. In the physical sciences, Mass and Weight are different properties Matter is commonly defined as being anything that has mass and that takes up space. Gravitation is a natural Phenomenon by which objects with Mass attract one another

However, the recognition of this difference is, historically, a relatively recent development and in many everyday situations the word "weight" continues to be used when "mass" is meant. For example, we say that an object "weighs one kilogram", even though the kilogram is a unit of mass.

The distinction between mass and weight is unimportant for many practical purposes because the strength of gravity is very simliar everywhere on the surface of the Earth. In such a constant gravitational field, the gravitational force exerted on an object (its weight) is directly proportional to its mass. This article is about proportionality the mathematical relation So, if object A weighs, say, 10 times as much as object B, then object A's mass is 10 times that of object B. This means that an object's mass can be measured indirectly by its weight (for conversion formulas see below). For example, when we buy a bag of sugar we can measure its weight (how hard it presses down on the scales) and be sure that this will give a good indication of the quantity that we are actually interested in, which is the mass of sugar in the bag. Nevertheless, slight variations in the Earth's gravitational field do exist (see Earth's gravity). Earth's gravity, denoted by g, refers to the Gravitational attraction that the Earth exerts on objects on or near its surface These alter the relationship between weight and mass, and must be taken into account in high precision weight measurements that are intended to indirectly measure mass.

The use of "weight" for "mass" also persists in some scientific terminology – for example, in the chemical terms "atomic weight", "molecular weight", and "formula weight", rather than the preferred "atomic mass" etc. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties The atomic mass (ma is the Mass of an atom most often expressed in unified atomic mass units The atomic mass may be considered to be the total mass

The difference between mass and force becomes obvious when:

• objects are compared in different gravitational fields, such as away from the Earth's surface. For example, on the surface of the Moon, gravity is only about one-sixth as strong as on the surface of the Earth. A one-kilogram mass is still a one-kilogram mass (as mass is an intrinsic property of the object) but the downward force due to gravity is only one-sixth of what the object would experience on Earth.

• masses are considered in the context of a lever, such as a cantilever structure or a weighing balance. A cantilever is a beam supported on only one end The beam carries the load to the support where it is resisted by moment and Shear stress. A weighing scale (usually just "scale" in common usage except in Australian English where "scales" is more common is a Measuring instrument for

• locating the center of gravity of an object (although if the gravitation field is uniform, the center of gravity will coincide with the center of mass).

• an object is submersed in a fluid (for instance, a brick weighs less when placed in water, and helium balloon in the atmosphere appears to have negative weight).

Units of weight

Systems of units of weight (force) and mass have a tangled history, partly because the distinction was not properly understood when many of the units first came into use.

Three approaches to mass and force units

System	Gravitational		Engineering		Absolute
Force (F)	F = m·a		F = m·a/gc = w·a/g		F = m·a
Weight (w)	w = m·g		w = m·g/gc ≈ m		w = m·g
Units	English	Metric	English	Metric	English	Metric
Acceleration (a)	ft/s2	m/s2	ft/s2	m/s2	ft/s2	m/s2
Mass (m)	slug	hyl	pound-mass	kilogram	pound	kilogram
Force (F)	pound	kilopond	pound-force	kilopond	poundal	newton

SI units

In most modern scientific work, physical quantities are measured in SI units. Newton's laws of motion are three Physical laws which provide relationships between the Forces acting on a body and the motion of the The slug is an English unit of Mass. It is a mass that accelerates by 1 ft/s² when a force of one Pound-force (lbf is exerted on it In the gravitational metric system(s the base unit of force is not normalised to one mass unit ( Gram or Kilogram) times one length unit ( Metre or centimetre The pound or pound-mass (abbreviation lb, lbm, or sometimes in the United States #) is a unit of Mass The unit kilogram-force ( kgf, often incorrectly just kg) or kilopond ( kp) is defined as the Force exerted by Earth's gravity This article deals with the unit of force For the unit of mass see Pound (mass. The poundal is a non- SI unit of Force. It is a part of the Foot-pound-second system of units a coherent subsystem of English units introduced The newton (symbol N) is the SI derived unit of Force, named after Isaac Newton in recognition of his work on Classical The SI unit of mass (and hence weight in some everyday senses)^[3] is the kilogram. The SI unit of force (and hence weight in the mechanics sense) is the newton (N) – which can also be expressed in SI base units as kg·m/s² (kilograms times metres per second squared). Mechanics ( Greek) is the branch of Physics concerned with the behaviour of physical bodies when subjected to Forces or displacements The newton (symbol N) is the SI derived unit of Force, named after Isaac Newton in recognition of his work on Classical The International System of Units (SI defines seven dimensionally independent SI base units.

The gravitational force exerted on an object is proportional to the mass of the object, so it is reasonable to think of the strength of gravity as measured in terms of force per unit mass, that is, newtons per kilogram (N/kg). However, the unit N/kg resolves to m/s²; (metres per second per second), which is the SI unit of acceleration, and in practice gravitational strength is usually quoted as an acceleration.

The pound and other non-SI units

In United States customary units, the pound can be either a unit of force or a unit of mass. US customary units, also known in the United States as English units or Imperial units (in reference to the British Empire) (but see English Related units used in some distinct, separate subsystems of units include the poundal and the slug. The poundal is a non- SI unit of Force. It is a part of the Foot-pound-second system of units a coherent subsystem of English units introduced The slug is an English unit of Mass. It is a mass that accelerates by 1 ft/s² when a force of one Pound-force (lbf is exerted on it The poundal is defined as the force necessary to accelerate a one-pound object at 1 ft/s², and is equivalent to about 1/32 of a pound (force). The slug is defined as the amount of mass that accelerates at 1 ft/s² when a pound of force is exerted on it, and is equivalent to about 32 pounds (mass).

The kilogram-force is a non-SI unit of force, defined as the force exerted by a one-kilogram mass in standard Earth gravity (equal to 9. The unit kilogram-force ( kgf, often incorrectly just kg) or kilopond ( kp) is defined as the Force exerted by Earth's gravity 80665 newtons exactly). The dyne is the cgs unit of force and is not a part of SI, while weights measured in the cgs unit of mass, the gram, remain a part of SI. The centimetre-gram-second system ( CGS) is a system of physical units.

Conversion between weight (force) and mass

To convert between weight (force) and mass we use Newton's second law, F = ma (force = mass × acceleration). Here, F is the force (weight) due to gravity, m is the mass of the object in question, and a is the acceleration due to gravity, on Earth approximately 9. 8 m/s² or 32. 2 ft/s². In this context the same equation is often written as W = mg, with W standing for weight, and g for the acceleration due to gravity.

Sensation of weight

See also: apparent weight

The weight force that we actually sense is not the downward force of gravity, but the normal force (an upward contact force) exerted by the surface we stand on, which opposes gravity and prevents us falling to the center of the Earth. In Physics, the normal force F_n\ (or in some books N) is the component perpendicular to the surface of contact of the Contact force In Physics, a contact force is a force between two objects (or an object and a surface that are in contact with each other This normal force, called the apparent weight, is the one that is measured by a spring scale.

For a body supported in a stationary position, the normal force balances the earth's gravitational force, and so apparent weight has the same magnitude as actual weight. (Technically, things are slightly more complicated. For example, an object immersed in water weighs less, according to a spring scale, than the same object in air; this is due to buoyancy, which opposes the weight force and therefore generates a smaller normal. In Physics, buoyancy ( BrE IPA: /ˈbɔɪənsi/ is the upward Force on an object produced by the surrounding liquid or gas in which it is These and other factors are explained further under apparent weight. )

If there is no contact with any surface to provide such an opposing force then there is no sensation of weight (no apparent weight). This happens in free-fall, as experienced by sky-divers (until they approach terminal velocity) and astronauts in orbit, who feel "weightless" even though their bodies are still subject to the force of gravity: they're just no longer resisting it. Free fall is motion with no Acceleration other than that provided by Gravity. A free falling object achieves its terminal velocity when the downward force of gravity ( Fg)equals the upward force of drag ( Fd) Weightless is the debut album by rap group The Skinny Boys. It was released in 1986 for Warlock Records and was produced by Mark Bush and Chuck The experience of having no apparent weight is also known as microgravity.

A degree of reduction of apparent weight occurs, for example, in elevators. In an elevator, a spring scale will register a decrease in a person's (apparent) weight as the elevator starts to accelerate downwards. This is because the opposing force of the elevator's floor decreases as it accelerates away underneath one's feet.

Measuring weight

Main article: Weighing scale

Weight is commonly measured using one of two methods. A weighing scale (usually just "scale" in common usage except in Australian English where "scales" is more common is a Measuring instrument for A spring scale or hydraulic or pneumatic scale measures weight force (strictly apparent weight force) directly. A weighing scale (usually just "scale" in common usage except in Australian English where "scales" is more common is a Measuring instrument for A weighing scale (usually just "scale" in common usage except in Australian English where "scales" is more common is a Measuring instrument for If the intention is to measure mass rather than weight, then this force must be converted to mass. As explained above, this calculation depends on the strength of gravity. Household and other low precision scales that are calibrated in units of mass (such as kilograms) assume roughly that standard gravity will apply. Standard gravity, usually denoted by g 0 or g n is the nominal acceleration due to gravity at the Earth's surface at sea level However, although nearly constant, the apparent or actual strength of gravity does in fact vary very slightly in different places on the earth (see standard gravity, physical geodesy, gravity anomaly and gravity). Standard gravity, usually denoted by g 0 or g n is the nominal acceleration due to gravity at the Earth's surface at sea level Physical geodesy is the study of the physical properties of the Gravity field of the Earth the Geopotential, with a view to their application in Geodesy A gravity anomaly is the difference between the observed Gravity and a value predicted from a model Gravitation is a natural Phenomenon by which objects with Mass attract one another This means that same object (the same mass) will exert a slightly different weight force in different places. High precision spring scales intended to measure mass must therefore be calibrated specifically according their location on earth.

Mass may also be measured with a balance, which compares the item in question to others of known mass. A weighing scale (usually just "scale" in common usage except in Australian English where "scales" is more common is a Measuring instrument for This comparison remains valid whatever the local strength of gravity. If weight force, rather than mass, is required, then this can be calculated by multiplying mass by the acceleration due to gravity – either standard gravity (for everyday work) or the precise local gravity (for precision work).

Gross weight is a term that generally is found in commerce or trade applications, and refers to the gross or total weight of a product and its packaging. Conversely, net weight refers to the intrinsic weight of the product itself, discounting the weight of packaging or other materials.

Relative weights on the Earth, other planets and the Moon

Main article: Earth's gravity

The table below shows comparative gravitational accelerations at the surface of the Sun, the Earth's moon, each of the planets in the solar system, and Pluto. Earth's gravity, denoted by g, refers to the Gravitational attraction that the Earth exerts on objects on or near its surface The “surface” is taken to mean the cloud tops of the gas giants (Jupiter, Saturn, Uranus and Neptune). A gas giant (sometimes also known as a Jovian planet after the planet Jupiter, or giant planet) is a large Planet that is not primarily For the Sun, the surface is taken to mean the photosphere. The values in the table have not been de-rated for the centrifugal effect of planet rotation (and cloud-top wind speeds for the gas giants) and therefore, generally speaking, are similar to the actual gravity that would be experienced near the poles.

Body	Multiple of Earth gravity	m/s²
Sun	27. The Sun (Sol is the Star at the center of the Solar System. 90	274. 1
Mercury	0. 3770	3. 703
Venus	0. The VENUS ( V ictoria E xperimental N etwork U nder the S ea project is a cabled sea floor observatory operated by the University 9032	8. 872
Earth	1 (by definition)	9. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 8226[4]
Moon	0. 1655	1. 625
Mars	0. 3895	3. 728
Jupiter	2. 640	25. 93
Saturn	1. 139	11. 19
Uranus	0. 917	9. 01
Neptune	1. Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. 148	11. 28
Pluto	0. 0621	0. 610

References

[edit] See also

• Weights and measures
• Ancient weights and measures
• Medieval weights and measures
• Atomic weight
• Human weight
• Body Mass Index
• Curb weight

In the Physical sciences weight is a Measurement of the gravitational Force acting on an object A system of measurment is a set of units which can be used to specify anything which can be measured and were historically important regulated and defined because of Trade and A system of measurment is a set of units which can be used to specify anything which can be measured and were historically important regulated and defined because of Trade and The atomic mass (ma is the Mass of an atom most often expressed in unified atomic mass units The atomic mass may be considered to be the total mass The body mass index ( BMI) or Quetelet index, is a statistical measurement which compares a person's weight and height Curb weight is the total Weight of a Vehicle with standard equipment all necessary operating Consumables (e

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