# Define mass, volume, time and temperature The inertial mass of a body is its physical property that indicates the amount of its inertia (`F = m_i*a)` . The gravitational mass of a body is its physical property that bends (warps) the 4 dimensional space around it (`Gamma = G*m_g/R^2` ). It has been show that the inertial mass is equal to the gravitational mass (`m_i =m_g`) .

The volume of a body is the amount of 3 dimensional space filled by its mass (or the amount of space required by its mass to exist).

By definition time is a dimension of the 4 dimensional space. It is proportional to the amount of total entropy (disorder) that exists in the Universe. Time axis has only one absolute direction (from the past to the future - the way in which total entropy is increasing) in contrast with other 3 spatial dimensions which can take two absolute directions (towards positive and negative values)

Temperature is the physical property of a body that is proportional to the amount of internal energy of the body. The internal energy of the body is the sum of the energies of all the body constituents (molecules or atoms). Therefore temperature is the physical property that generally speaking is proportional to the kinetic energy of the molecules of a body.

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