Basic Definitions in Physics

Density

The density is the mass of a substance per unit volume.

Pressure

The pressure is the force acting normally on unit area of a surface.

Stress

Stress is the force per unit area of cross section.

Strain

Strain is the extension per unit length.

Young Modulus

The young modulus is the ratio of stress applied to a body to strain produced.

Specific Heat Capacity

The Specific Heat Capacity is the heat energy required to increase the temperature of 1 kg by 1 K.

Molar heat capacity

The molar heat capacity is the ratio of heat supplied to unit amount of a substance to its consequent rise in temperature.

Specific latent heat

The specific latent heat of fusion or vaporization is the heat energy required to change the state of 1 kg of material from solid to liquid or liquid to vapor without change of temperature.

Activity

The activity is the number of disintegrations per second.

Decay constant

The decay constant is the probability of each atom of a source decaying in one second (s ^-1).

Half Life

The half life is the time taken for the number of atoms of that isotope to decrease to half the initial number.