Energy [addendum] | Research & Encyclopedia Articles

Energy [addendum]

Force is among the most fundamental concepts in Newtonian physics. Energy became an important unifying concept in nineteenth-century physics. Energy and force take on somewhat different roles in relativity and quantum mechanics.

Force in Classical Physics

In classical physics, force is a vector quantity. Isaac Newton's second law of motion (F = ma) relates the net force (F) on a body to its mass (m) and acceleration (a) in an inertial reference frame. Newton's third law says that the force exerted by body A on body B is equal and opposite to the force that B exerts on A. To apply Newton's laws of motion in a non-inertial frame, correction factors with the dimensions of force ("pseudoforces") must be introduced, such as the Coriolis and centrifugal forces.

The constituents of a system of bodies (such as a macroscopic object) exert "internal forces" upon one another, whereas "external forces" are imposed on the system from without. By Newton's third law, the internal forces cancel. Newton's second law then applies to the system as a whole: The net external force on the system equals the product of the system's total mass (the sum of its constituents' masses) with the acceleration of its center of mass.

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