In
science and
engineering, the
weight of an object is usually taken to be the
force on the object due to
gravity. Weight is a
vector whose magnitude (a
scalar quantity), often denoted by an italic letter
W, is the product of the
mass m of the object and the magnitude of the local
gravitational acceleration g; thus: . 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. In this sense of weight, a body can be weightless only if it is far away (in principle infinitely far away) from any other mass. Although weight and mass are scientifically distinct quantities, the terms are often confused with each other in everyday use.