Gravity - Inryoku

The force that attracts two objects to each other is called gravity, and the force that repels two objects to each other is called repulsion. Also, since the force of gravity acting between objects is always gravitational, gravity is sometimes simply called gravity. The word gravitation refers to gravity.

The idea of ​​considering the action acting between spatially separated objects as "force" was established by Newtonian mechanics, and the "force" recognized at that time was the gravitational force between the Earth and an object, the Earth and the Moon, and the Sun and a planet. Due to this historical background, the concept of force itself is sometimes seen as the same as gravitational force. However, this concept of force can also be applied to electrical and magnetic forces, which have both attractive and repulsive forces, and even to the nuclear force acting between the protons and neutrons that make up atomic nuclei. The interactions between elementary particles are accurately described by quantum field theory, and the concepts of attraction and repulsion are no longer valid at this level. However, forces can be approximately constructed using quantum field theory, and the intuitively easy-to-understand concepts of attraction and repulsion are still useful in physics today.

[Fumitake Sato]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

互いに引き合う力を引力といい、互いに反発する力を斥力(せきりょく)という。また物質間に働く重力はつねに引力であるため、重力のことを単に引力とよぶ場合もある。万有引力ということばは重力をさす。

　空間的に離れた物質の間に働く作用を「力」としてとらえるのは、ニュートン力学により確立した考え方で、このときに認識されていた「力」は、地球と物体、地球と月、太陽と惑星の間の引力である。こうした歴史的経過のため、力の概念そのものと引力とが同一にみられる場合がある。しかし、引力と斥力がある電気、磁気の力にも、さらには原子核を構成する陽子、中性子間に働く核力にも、この力の概念は適用できる。素粒子間の相互作用は正確には場の量子論により記述され、この次元では引力、斥力という概念はもはや有効でない。しかし、場の量子論を用いて力を近似的に構成することはでき、直観的にわかりやすい引力、斥力の概念は現在でも物理学で有用である。

［佐藤文隆］

出典　小学館　日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について　情報 | 凡例