We all have an intuitive notion of force in our experience force is needed to push carry or throw objects deform or break them. We also experience the impact of forces on us,like when a moving objects hits us or were in a merry -go- round going from this intuitive notion to the proper scientific concepts of force is not a trivial matter.Early thinkers like Aristotle had wrong ideas about it .the correct notion of forces was arrived at by Isaac Newton in famous laws of motion. He also gave an explicit form for the force of gravitational attraction between two bodies we shall learn theses matters in substitutes or subsequently chapters.
In the macroscopic world ,besides the gravitational force we counter several kinds of forces (muscular forces contact forces ) between bodies ,friction the forces are exerted by compressed or elongated springs and taut springs and ropes the forces of buoyancy and viscous force when solids are in contact with forces due to present of pressure of fluid the force due to surface tension of a liquid and so on .There are also forces involving charged and magnetic bodies.In microscopic domain again.We have electric and magnetic forces, nuclear forces involving protons and neutrons inter atomic and inter molecular forces.
A great insight of the twentieth century physics is that these different forces occurring in different contexts actually arise from only a small number of fundamental forces in nature to the attraction /repulsion between the neighbouring atoms of spring when the spring is elongated \compressed this net attraction\repulsion can be traced to the sum of electric forces between the charged constituents of the atoms.
In principle this means that the laws for "derived "forces (such as spring force friction ) are not independent of the laws of fundamental forces in nature .The origin of these derived forces is however very complex.At the present stage of our understanding we know of four fundamental forces in nature which are described in brief.
