Gravitational Fields and Potentials - Vocabulary Flashcards

Vocabulary flashcards covering gravitational fields, Newton's law, circular orbits, geostationary orbits, and gravitational potential energy.

Gravitational Field

A region of space where a mass experiences a force due to the gravitational attraction of another mass.

Gravitational Field Strength (g)

The force per unit mass at a point in a gravitational field; g = F/m; units N kg^-1.

Weight

The gravitational force on a mass, W = mg.

Gravitational Constant (G)

The universal constant in Newton's law of gravitation that relates force to masses and distance: F = G m1 m2 / r^2.

Newton's Law of Gravitation

The gravitational force between two masses is proportional to the product of their masses and inversely proportional to the square of their separation.

Inverse Square Law

Gravitational force decreases with the square of the distance between masses.

Point Mass Approximation

For a body outside a uniform sphere, treat its mass as located at its centre when calculating gravitational effects.

Uniform Sphere

A sphere with mass distributed evenly; outside, its gravitational field is identical to that of a point mass at the centre.

Gravitational Field Lines

A visual representation of a gravitational field; lines show direction of the field, directed toward the attracting mass.

Radial Field

A non-uniform gravitational field where field strength varies with distance; field lines are directed toward the centre.

Uniform Field

A gravitational field with constant strength throughout, represented by parallel, equally spaced field lines.

Circular Orbit

An orbit of constant radius where gravity provides the centripetal force: F_g = m v^2 / r.

Centripetal Force

The inward force required to keep an object in circular motion; in gravity, provided by gravity.

Kepler's Third Law

For planets/satellites in circular orbits about the same central body, T^2 ∝ r^3.

Angular Speed (ω)

The rate of rotation, ω = v / r; for circular orbits ω^2 = GM / r^3.

Orbital Period (T)

Time to complete one orbit; T = 2π sqrt(r^3 / (GM)).

Geostationary Orbit

A circular orbit with T = 24 h directly above the equator; appears fixed from Earth and is used for communications.

Speed in Circular Orbit (v)

Linear speed in a circular orbit; v = sqrt(GM / r).

Gravitational Field Strength Equation

g = GM / r^2; shows how g falls off with distance as an inverse square.

Distance from Centre (r)

The distance from the centre of the mass producing the field to the point where g or φ is calculated.

Gravitational Potential (φ)

The gravitational potential energy per unit mass at a point; φ = - GM / r; φ → 0 as r → ∞.

Gravitational Potential Energy (GPE)

Energy of a mass in a gravitational field; U = m φ = - GM m / r.

Change in Gravitational Potential Energy (ΔGPE)

The difference in GPE between two positions; ΔGPE = m Δφ (or ΔGPE = φ(r2)m − φ(r1)m).