# Weight vs. Density

By Jaxson ## Main Difference

The main difference between Weight and Density is that the Weight is a force on the object due to gravity and Density is a mass per unit volume

• Weight

In science and engineering, the weight of an object is related to the amount of force acting on the object, either due to gravity or to a reaction force that holds it in place.

Some standard textbooks define weight as a vector quantity, the gravitational force acting on the object. Others define weight as a scalar quantity, the magnitude of the gravitational force. Others define it as the magnitude of the reaction force exerted on a body by mechanisms that keep it in place: the weight is the quantity that is measured by, for example, a spring scale. Thus, in a state of free fall, the weight would be zero. In this sense of weight, terrestrial objects can be weightless: ignoring air resistance, the famous apple falling from the tree, on its way to meet the ground near Isaac Newton, would be weightless.

The unit of measurement for weight is that of force, which in the International System of Units (SI) is the newton. For example, an object with a mass of one kilogram has a weight of about 9.8 newtons on the surface of the Earth, and about one-sixth as much on the Moon. Although weight and mass are scientifically distinct quantities, the terms are often confused with each other in everyday use (i.e. comparing and converting force weight in pounds to mass in kilograms and vice versa).

Further complications in elucidating the various concepts of weight have to do with the theory of relativity according to which gravity is modelled as a consequence of the curvature of spacetime. In the teaching community, a considerable debate has existed for over half a century on how to define weight for their students. The current situation is that a multiple set of concepts co-exist and find use in their various contexts.

• Density

The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ (the lower case Greek letter rho), although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume:

ρ

=

m

V

{displaystyle rho ={frac {m}{V}}}

where ρ is the density, m is the mass, and V is the volume. In some cases (for instance, in the United States oil and gas industry), density is loosely defined as its weight per unit volume, although this is scientifically inaccurate – this quantity is more specifically called specific weight.

For a pure substance the density has the same numerical value as its mass concentration.

Different materials usually have different densities, and density may be relevant to buoyancy, purity and packaging. Osmium and iridium are the densest known elements at standard conditions for temperature and pressure but certain chemical compounds may be denser.

To simplify comparisons of density across different systems of units, it is sometimes replaced by the dimensionless quantity “relative density” or “specific gravity”, i.e. the ratio of the density of the material to that of a standard material, usually water. Thus a relative density less than one means that the substance floats in water.

The density of a material varies with temperature and pressure. This variation is typically small for solids and liquids but much greater for gases. Increasing the pressure on an object decreases the volume of the object and thus increases its density. Increasing the temperature of a substance (with a few exceptions) decreases its density by increasing its volume. In most materials, heating the bottom of a fluid results in convection of the heat from the bottom to the top, due to the decrease in the density of the heated fluid. This causes it to rise relative to more dense unheated material.

The reciprocal of the density of a substance is occasionally called its specific volume, a term sometimes used in thermodynamics. Density is an intensive property in that increasing the amount of a substance does not increase its density; rather it increases its mass.

Wikipedia
• Weight (noun)

The force on an object due to the gravitational attraction between it and the Earth (or whatever astronomical object it is primarily influenced by).

• Weight (noun)

An object used to make something heavier.

• Weight (noun)

A standardized block of metal used in a balance to measure the mass of another object.

• Weight (noun)

Importance or influence.

• Weight (noun)

A disc of iron, dumbbell, or barbell used for training the muscles.

“He’s working out with weights.”

• Weight (noun)

Mass (net weight, atomic weight, molecular weight, troy weight, carat weight, etc.).

• Weight (noun)

A variable which multiplies a value for ease of statistical manipulation.

• Weight (noun)

The smallest cardinality of a base.

• Weight (noun)

The boldness of a font; the relative thickness of its strokes.

• Weight (noun)

The relative thickness of a drawn rule or painted brushstroke, line weight.

• Weight (noun)

The illusion of mass.

• Weight (noun)

The thickness and opacity of paint.

• Weight (noun)

Pressure; burden.

“the weight of care or business”

• Weight (noun)

The resistance against which a machine acts, as opposed to the power which moves it.

• Weight (noun)

Shipments of (often illegal) drugs.

“He was pushing weight.”

• Weight (verb)

To add weight to something; to make something heavier.

• Weight (verb)

To load, burden or oppress someone.

• Weight (verb)

To assign weights to individual statistics.

• Weight (verb)

To bias something; to slant.

• Weight (verb)

To handicap a horse with a specified weight.

• Weight (verb)

To give a certain amount of force to a throw, kick, hit, etc.

• Density (noun)

A measure of the mass of matter contained by a unit volume.

• Density (noun)

The ratio of one quantity to another quantity.

“The number of particles per unit volume of a specified volume can be considered to be the particle density for the specified volume.”

• Density (noun)

The probability that an event will occur, as a function of some observed variable.

Wiktionary