An Etymological Dictionary of Astronomy and Astrophysics
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The forces of jets from a comet's nucleus that can cause a rocket-like effect and alter a comet's direction of motion slightly.

→ non-; → gravitational; → force.

The force of → attraction between molecules of different substances; for example, the force between the molecules of a solid and a liquid. When water is poured on clean glass, it tends to spread, forming a thin, uniform film over the surface. This is because the adhesive forces between water and glass are strong enough to pull the water molecules out of their spherical formation and hold them against the surface of the glass, thus avoiding the repulsion between like molecules.

→ adhesive; → force.

The force exerted by a gaseous fluid upon a body completely immersed in it caused by their relative motion. The components of aerodynamic force are: → lift and → drag.

→ aerodynamic; → force.

A physical force (→ gravitational, → electric, → magnetic, etc.) by which a body attracts another.

→ attractive; → force.

The force that causes immersed bodies to float or rise to the surface of a liquid or upward in a gas. Buoyant force is produced by → gravity and density differences. Same as → buoyancy.

From buoy (current meaning) "a float moored in water to mark a location," from M.E. boye, from O.Fr. buie or M.Du. boeye, from L. boia "fetter, chain" + suffix -ant; → force.

A → force that is always directed toward a fixed point and whose → magnitude depends only on the distance from that point. Mathematically, F is a central force if and only if: F = f(r)r₁ = f(r)r/r, where r₁ = r/r is a unit → vector in the direction of r. If f(r) < 0 the force is said to be → attractive toward the source. If f(r) > 0 the force is said to be → repulsive from the source. In other words, a central force is one whose → potential, V(r), depends only on the → distance from the source. → Gravitational force and → electrostatic force are central, with V(r)∝ 1/r.

→ central; → force.

A force in a rotating reference frame directed outward from the axis of rotation.

→ centrifugal; → force.

The force exerted on an object in → circular motion which is directed toward the center and keeps the body in motion. Centripetal force produces → centripetal acceleration, according to → Newton's second law: F_c = ma_c. Its direction is always inward along the → radius vector, and its magnitude is given by: F_c= ma_c = mv_t²/r = mω²r.

→ centripetal; → force.

The strength of an external → magnetic field that brings to zero the → magnetic flux density of a magnetic material when that field is caused to operate in the opposite direction from the orientation of the → magnetization of the material. Also called coercivity. Coercive force is a measure of the magnetization of a → ferromagnetic material. It is usually measured in the units of → oersted or ampere/m.

→ coercive; → force.

The force of → attraction between the molecules of the same substance.

→ cohesive; → force.

A system of two or more forces that lie along the same → line of action.

→ collinear; → force.

A system of forces applied to a → rigid body in such manner that their lines of action intersect at a single point. A system of concurrent forces acting on a rigid body can be replaced by an equivalent force applied at the same point. → line of action.

→ concurrent; → force.

A system of forces acting on a body that all are in the same plane.

→ com- + planar adj. from → plane.

An apparent, rather than real, force exerted on a body when it moves in a rotating → reference frame. Same as the → Coriolis effect.

→ Coriolis effect; → force.

An attractive or repulsive → electrostatic force between objects bearing electric charge, as described by → Coulomb's law. If the charges are of opposite sign, then the force is attractive; if thy are of the same sign, the force is repulsive.

→ Coulomb; → force.

The fundamental force that is associated with electric and magnetic fields. One of the four fundamental forces of nature, it is carried by photons.

→ electromagnetic; → force.

The force, analogous to a pressure, which maintains a flow of electricity through a closed circuit. It is the algebraic sum of the → potential differences acting in the circuit. The unit of electromotive force is the → volt.

From → electro- + motive, from M.E., from M.Fr., from O.Fr. motif, from M.L. motivus "moving, impelling," from L. motus, p.p. of movere "to move," → motion; → force.

Niru, → force; barqrân, literally "driving electricity," from barq, → electro- + rân present stem of rândan, → drive.

The force that takes part in an → electroweak interaction.

→ electroweak; → force.

The force that governs the exchange of particles in the interaction between bodies. → exchange particle.

→ exchange, → force.

The region of → space surrounding a body, such as a mass of → matter, a → charged particle, or a → magnet, within which it can exert a → force on another similar body not in contact with it.

→ field; → force.