Particle: A particle is a body of negligible dimensions.

Scalar quantities : These are the quantities characterized by only magnitude, such as mass, temperature.

Vector quantities : These are the quantities characterized by magnitude and direction, such as velocity, force. We will indicate vector quantities by boldfaced letters.

Free vector : It is a vector, whose action is not confined to or associated with a unique line in space. Only, the direction and magnitude of the vector remains fixed.

Sliding vector : It is a vector, which may be moved along the lines of action without change of meaning. For example, in towing a cart, we may apply the force anywhere along the rope.

Bound vector : It is a vector, which must be applied at definite point. For example, if we are interested in the deformation of body, we must be concerned with the point of application of forces.

Concurrent forces: Two or more forces are said to be concurrent at a point if their lines of action intersect at that point. shows 3 concurrent forces.