# Mass versus weight

**weightdistinctionhistorical conflation of mass and weightmass and weightmass or weightsingle-pan**

In common usage, the mass of an object is often referred to as its weight, though these are in fact different concepts and quantities.wikipedia

59 Related Articles

### Mass

**inertial massgravitational massweight**

In common usage, the mass of an object is often referred to as its weight, though these are in fact different concepts and quantities.

But because of slight differences in the strength of the Earth's gravitational field at different places, the distinction becomes important for measurements with a precision better than a few percent, and for places far from the surface of the Earth, such as in space or on other planets.

### Pound (mass)

**lbpoundspound**

For example, in retail commerce, the "net weight" of products actually refers to mass, and is expressed in mass units such as grams or ounces (see also Pound: Use in commerce). 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.

Usage of the unqualified term pound reflects the historical conflation of mass and weight.

### Kilogram

**kgmgmilligram**

In other words, an object with a mass of 1.0 kilogram will weigh approximately 9.81 newtons on the surface of the Earth (its mass multiplied by the gravitational field strength), since the newton is a unit of force, while the kilogram is a unit of mass. The object's weight will be less on Mars (where gravity is weaker), more on Saturn, and negligible in space when far from any significant source of gravity, but it will always have the same mass. Under Sir Isaac Newton's 332-year-old laws of motion and an important formula that sprang from his work, F = ma, an object with a mass, m, of one kilogram will accelerate, a, at one meter per second per second (about one-tenth the acceleration due to earth’s gravity) when acted upon by a force, F, of one newton.

The Kibble balance (known as a "watt balance" before 2016) is essentially a single-pan weighing scale that measures the electric power necessary to oppose the weight of a kilogram test mass as it is pulled by Earth's gravity.

### Imperial units

**imperialimperial systemimperial unit**

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.

The distinction between mass and weight is not always clearly drawn.

### Weighing scale

**scalesscalebalance**

When one stands on a balance-beam-type scale at a doctor’s office, they are having their mass measured directly.

Mass versus weight

### Pound (force)

**lbflb f pounds-force**

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.

Mass versus weight for the difference between the two physical properties

### Weight

**gross weightweighingweigh**

In common usage, the mass of an object is often referred to as its weight, though these are in fact different concepts and quantities.

### Matter

**corporealsubstancematerial**

In scientific contexts, mass is the amount of "matter" in an object (though "matter" may be difficult to define), whereas weight is the force exerted on an object by gravity.

### Force

**forcesattractiveforce vector**

In scientific contexts, mass is the amount of "matter" in an object (though "matter" may be difficult to define), whereas weight is the force exerted on an object by gravity.

### Earth

**terrestrialworldGlobal**

In other words, an object with a mass of 1.0 kilogram will weigh approximately 9.81 newtons on the surface of the Earth (its mass multiplied by the gravitational field strength), since the newton is a unit of force, while the kilogram is a unit of mass. The object's weight will be less on Mars (where gravity is weaker), more on Saturn, and negligible in space when far from any significant source of gravity, but it will always have the same mass.

### Gravity

**gravitationgravitationalgravitational force**

In other words, an object with a mass of 1.0 kilogram will weigh approximately 9.81 newtons on the surface of the Earth (its mass multiplied by the gravitational field strength), since the newton is a unit of force, while the kilogram is a unit of mass. The object's weight will be less on Mars (where gravity is weaker), more on Saturn, and negligible in space when far from any significant source of gravity, but it will always have the same mass. In scientific contexts, mass is the amount of "matter" in an object (though "matter" may be difficult to define), whereas weight is the force exerted on an object by gravity.

### Newton (unit)

**kNnewtonN**

In other words, an object with a mass of 1.0 kilogram will weigh approximately 9.81 newtons on the surface of the Earth (its mass multiplied by the gravitational field strength), since the newton is a unit of force, while the kilogram is a unit of mass. The object's weight will be less on Mars (where gravity is weaker), more on Saturn, and negligible in space when far from any significant source of gravity, but it will always have the same mass. Under Sir Isaac Newton's 332-year-old laws of motion and an important formula that sprang from his work, F = ma, an object with a mass, m, of one kilogram will accelerate, a, at one meter per second per second (about one-tenth the acceleration due to earth’s gravity) when acted upon by a force, F, of one newton.

### Mars

**Martianplanet MarsRed Planet**

In other words, an object with a mass of 1.0 kilogram will weigh approximately 9.81 newtons on the surface of the Earth (its mass multiplied by the gravitational field strength), since the newton is a unit of force, while the kilogram is a unit of mass. The object's weight will be less on Mars (where gravity is weaker), more on Saturn, and negligible in space when far from any significant source of gravity, but it will always have the same mass.

### Saturn

**Saturn's atmosphereExploration of Saturnhome planet**

In other words, an object with a mass of 1.0 kilogram will weigh approximately 9.81 newtons on the surface of the Earth (its mass multiplied by the gravitational field strength), since the newton is a unit of force, while the kilogram is a unit of mass. The object's weight will be less on Mars (where gravity is weaker), more on Saturn, and negligible in space when far from any significant source of gravity, but it will always have the same mass.

### Buoyancy

**buoyantbuoyant forcefloat**

Similarly, a balloon has mass but may appear to have no weight or even negative weight, due to buoyancy in air.

### Inertia

**inertialinertia forceinertial forces**

A better scientific definition of mass is its description as being composed of inertia, which is the resistance of an object being accelerated when acted on by an external force.

### Theory of relativity

**relativityrelativisticrelativity theory**

While the weight of an object varies in proportion to the strength of the gravitational field, its mass is constant (ignoring relativistic effects) as long as no energy or matter is added to the object.

### Isaac Newton

**NewtonSir Isaac NewtonNewtonian**

Under Sir Isaac Newton's 332-year-old laws of motion and an important formula that sprang from his work, F = ma, an object with a mass, m, of one kilogram will accelerate, a, at one meter per second per second (about one-tenth the acceleration due to earth’s gravity) when acted upon by a force, F, of one newton.

### Newton's laws of motion

**laws of motionNewton's second lawNewton's second law of motion**

Under Sir Isaac Newton's 332-year-old laws of motion and an important formula that sprang from his work, F = ma, an object with a mass, m, of one kilogram will accelerate, a, at one meter per second per second (about one-tenth the acceleration due to earth’s gravity) when acted upon by a force, F, of one newton.

### Acceleration

**decelerationacceleratem/s 2**

Under Sir Isaac Newton's 332-year-old laws of motion and an important formula that sprang from his work, F = ma, an object with a mass, m, of one kilogram will accelerate, a, at one meter per second per second (about one-tenth the acceleration due to earth’s gravity) when acted upon by a force, F, of one newton.

### Metre per second squared

**m/s 2 meters per second squaredm/s²**

### Gravity of Earth

**ggravityEarth's gravity**

### Bowling ball

**bowling ballsballbowling ball coverstock**

Inertia is seen when a bowling ball is pushed horizontally on a level, smooth surface, and continues in horizontal motion.

### Inelastic collision

**inelasticinelastic collisionsinelastic events**

Consequently, whenever 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.

### Elastic collision

**elasticbouncescollision**

Consequently, whenever 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.