mechanics

In mechanics, the resolution of forces is the division of a single force into two parts that act at right angles to each other. In the diagram, the weight W of an object on a slope, tilted at an angle θ, can be resolved into two parts or components: one acting at a right angle to the slope, equal to W cos θ, and one acting parallel to and down the slope, equal to W sin θ.

Branch of physics dealing with the motions of bodies and the forces causing these motions, and also with the forces acting on bodies in equilibrium. It is usually divided into dynamics and statics.

Quantum mechanics is the system based on quantum theory, which has superseded Newtonian mechanics in the interpretation of physical phenomena on the atomic scale.

Machines As well as dealing with the direct action of forces on bodies, mechanics studies the nature and action of forces when they act on bodies by the agency of machinery. This gives the origin of the word ‘mechanics’: in its early stages it was the science of making machines. A machine in mechanics means any contrivance in which a force applied at one point is made to raise weight or overcome a resisting force acting at another point. All machines can be resolved into three primary machines: the lever, the inclined plane, and the wheel and axle.

History Mechanics is of the utmost importance in structural engineering and is essentially experimental. Its laws are based on intuitive deductions from experimental observations. The Greek mathematician Archimedes, by his investigations of the principle of the lever and the property of the centre of gravity, established mechanics as a science. After Archimedes little progress was made until the time of Stevinus (1548–1620), who investigated the principle of the inclined plane. Aristotle had taught that the speed with which a body falls is directly proportional to its weight, but in the 16th century Galileo proved this to be false, and he subsequently deduced the solution to the problems of falling bodies, re-examining the previous knowledge of mechanics. Isaac Newton took up the subject after Galileo, and his three laws remain the fundamental laws of nonrelativistic mechanics today. His theory of universal gravitation enabled him to account for the motions of the members of the Solar System as well as the motion of bodies on the Earth. The French mathematicians Joseph Lagrange and Pierre Laplace developed the subject in the 18th century. The formulation of the theory of relativity by Albert Einstein led to a complete revision of the fundamentals of mechanics. When the bodies considered in a problem in mechanics have velocities (relative to a frame which is moving with a uniform or zero velocity with respect to the fixed stars) which are small compared with that of light, the old Newtonian or nonrelativistic mechanics still holds. But for larger velocities, important differences are predicted by relativity theory, and many have been confirmed by experiment.