An Etymological Dictionary of Astronomy and Astrophysics
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The attractive force which acts between nucleons when they are extremely close together (closer than 10^-13 cm).

→ nuclear; → force.

A force resulting from → pressure gradient that is directed from high to low pressure.

→ pressure; → gradient; → force.

The force by which bodies repel one another. → repulsion.

Repulsive, adj. of → repulse; → force.

Finding the → components of a → force which act in specified → directions.

→ resolution; → force.

A force that comes into play after a system is perturbed away from the equilibrium, tending to bring the system back the equilibrium position. For example, when a pendulum is displaced from its equilibrium position, it is subject to a restoring force due to gravity that will accelerate it back toward the equilibrium position. The restoring force combined with the pendulum's mass causes it to oscillate about the equilibrium position.

→ restore; → force.

A single force which has the same effect as all other applied forces collectively.

→ resultant; → force.

The force responsible for holding quarks and gluons together to form protons, neutrons and other particles. It is the strongest of the four fundamental forces. Same as → strong interaction.

→ strong; → force.

The force tending to stretch (or produce tension in) an object

→ tensile; → force.

The → gravitational force exerted on an extended body as a result of the difference in the strength of gravity between near and far parts of the body. The ocean tides on Earth result from the varying gravitational force of the Moon exerted on the Earth's oceans closest and farthest from the Moon. Tidal force, which is the → gradient of the gravitational force, varies as 1/r³. More specifically, F_tidal = dF/dr = (2GMm)/r³, where M is mass of the → primary body, m is mass of the → secondary body, r is distance between objects, and G the → gravitational constant. The total tidal force experienced across a body is equal to the tidal force (force per unit distance) multiplied by the diameter of that body: F_tt = F_tidal x 2R (provided that radius R is much smaller than r). It is obvious that the tidal force experienced by Earth at Moon's → perigee is larger than that at the → apogee. If the tidal force is stronger than a body's cohesiveness, the body will be disrupted. The minimum distance that a secondary comes to a primary before it is shattered by tidal force is called its → Roche limit. Tidal forces create → tidal heating.

→ tidal; → force.

A weak attractive force between neutral atoms and molecules arising from polarization induced in each particle by the presence of other particles. All molecules contain electrically charged particles, and even though the molecule as a whole is electrically neutral there do exist between molecules van der Waals attractive forces of electric origin.

Named after Dutch physicist Johannes Diderik van der Waals (1837-1923), Nobel Prize in Physics 1910; → force.

The force per unit volume or per unit mass arising from the action of tangential stresses in a moving → viscous fluid.

→ viscous; → force.

Same as → weak interaction.

→ weak; → force.

Same as → weak interaction.

→ weak; → nuclear; → force.