Order from Force: A natural history of the vacuum by Jeffrey H Williams

Author:Jeffrey H Williams
Language: eng
Format: epub
ISBN: 9781681742410
Publisher: IOP Publishing
Published: 2015-11-06T00:00:00+00:00

8.2 Some early history

The study of the forces of nature began in the classical world, when philosophers used the concept of force in their investigations of stationary and moving objects. Analysis of the characteristics of forces culminated in the work of Archimedes who formulated a theory of the forces inherent in fluids (that result in buoyancy) and astonished spectators when he single-handedly launched a large ship using appropriately sized and placed pulleys and levers. As he supposedly said, ‘Give me a place to stand, and I shall move the Earth’.

Aristotle provided a philosophical framework for the concept of a force as an integral part of Aristotelian cosmology. Aristotle held that the natural world was made of four elements (air, earth, fire and water) that existed in ‘natural states’. He believed that it was the natural state of objects with mass, such as the elements water and earth, to be motionless on the ground and that they tended towards that state if left alone. He distinguished between the innate tendency of objects to find their natural place, for example, for heavy bodies to fall, which led to natural motion, and unnatural or forced motion, which required continued application of a force. This theory, based on observations of how objects move, such as the constant application of a force needed to keep a cart moving, was however incapable of accounting for the behaviour of projectiles, such as the flight of an arrow.

The shortcomings of Aristotelian physics would not be fully corrected until the 17th century, when Galileo Galilei was influenced by the late-medieval idea that objects in forced motion carry an innate force or impetus. Galileo devised and constructed an experiment in which various sized stones and cannonballs were rolled down a smooth incline to disprove the Aristotelian theory of motion. He showed that the bodies were accelerated by gravity to an extent that was independent of their mass and argued that objects retain their velocity unless acted on by another force, for example friction (a manifestation of electromagnetism).

Sir Isaac Newton attempted to describe the motion of all objects using the concepts of inertia (the resistance of any object to a change in its state of motion or rest) and force, and in so doing he discovered that all the objects he investigated obeyed certain conservation laws. In 1687 Newton published his influential Philosophiae Naturalis Principia Mathematica, where he set out his three laws of motion, which have remained the way forces are described in physics.

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