Gravity - Gravity is most commonly thought of as the agency that gives objects weight.
Applied Concept: Gravity is a natural phenomenon and one of those fundamental forces by which all objects with mass attract each other. It is responsible for keeping the earth and other planets in orbit around the sun and for keeping people on the earth.

Weight - Weight is the heaviness of an object.
Applied Concept: Weight can be defined as either the actual (physical) or apparent (visual) heaviness of an object or shape. Apparent weight is the illusion of weight – or heaviness – created by a shape or object.

Mass - Mass can be defined as the quantity of matter that an object contains. Mass refers to the degree of volume and density of a material.
Applied Concept: Steel, for example, has more mass than and equal volume of Styrofoam – steel is a dense material and Styrofoam is mostly air. Typically, the more mass something has, the heavier it is.

Balance - Balance is the stability produced by the even distribution of weight.
Applied Concept: Balance may either be true physical equilibrium – where the physical forces (like gravity) acting on an object are stable – or it can be an applied visual principle. Visual balance refers to the way elements of a design or object are arranged to create a feeling of stability.