In physical science, mass refers to the degree of acceleration a body acquires when subject to a force: bodies with
greater mass are accelerated less by the same force. One says the body of greater mass has greater inertia. The
mass of an amount of matter in a chemical substance is determined in part by the number and type of atoms or
molecules it contains, and in part by the energy involved in binding it together. According to special relativity, energy
also has mass according to the principle of mass–energy equivalence as exemplified in the process of nuclear
fusion and the bending of light.
In everyday usage, mass is commonly confused with weight. But, in physics and engineering, weight means the
strength of the gravitational pull on the object; that is, how heavy it is, measured in units of newtons. In everyday
situations, the weight of an object is proportional to its mass, which usually makes it unproblematic to use the
same word for both concepts. However, the distinction between mass and weight becomes important for
measurements with a precision better than a few percent (due to slight differences in the strength of the Earth's
gravitational field at different places), and for places far from the surface of the Earth, such as in space or on other
The volume of any solid, fluid, plasma, vacuum or theoretical object is how much three-dimensional space it
occupies, often quantified numerically. One-dimensional figures (such as lines) and two-dimensional shapes
(such as squares) are assigned zero volume in the three-dimensional space. Volume is presented as mL or cm3
(milliliters or cubic centimeters).
Volumes of straight-edged and circular shapes are calculated using arithmetic formulas. Volumes of other curved
shapes are calculated using integral calculus, by approximating the given body with a large number of small cubes
or concentric cylindrical shells, and adding the individual volumes of those shapes. The volume of irregularly
shaped objects can be determined by displacement. If an irregularly shaped object is less dense than the fluid, you
will need a weight to attach to the floating object. A sufficient weight will cause the object to sink. The final volume of
the unknown object can be found by subtracting the volume of the attached heavy object and the total fluid volume
In differential geometry, volume is expressed by means of the volume form, and is an important global Riemannian
Volume and capacity are sometimes distinguished, with capacity being used for how much a container can hold
(with contents measured commonly in liters or its derived units), and volume being how much space an object
displaces (commonly measured in cubic meters or its derived units). The volume of a dispersed gas is the
capacity of its container. If more gas is added to a closed container, the container expands (as in a balloon), the
pressure inside the container increases, or both.
Volume and capacity are also distinguished in a capacity management setting, where capacity is defined as
volume over a specified time period.
Volume is a fundamental parameter in thermodynamics and it is conjugate to pressure.
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