Kepler’s Laws & Newtonian Gravitation

Vocabulary flashcards covering Kepler’s three laws, Newton’s Law of Universal Gravitation, related terms, and classroom gravity demonstrations.

Kepler’s First Law (Law of Ellipses)

Planets move in elliptical orbits with the Sun located at one focus.

Kepler’s Second Law (Law of Equal Areas)

A line connecting a planet to the Sun sweeps out equal areas in equal time intervals.

Kepler’s Third Law (Harmonic Law)

Describes the relationship between a planet’s orbital period and its average distance from the Sun (T² ∝ r³).

Orbital Period

The time a planet takes to complete one full orbit around the Sun.

Newton’s Law of Universal Gravitation

Every object attracts every other object with a force proportional to the product of their masses and inversely proportional to the square of the distance between their centers.

Gravitational Constant (G)

The proportionality constant in Newton’s law; equal to 6.674 × 10⁻¹¹ N·m²/kg².

Gravitational Force (F)

The attractive force between two masses, calculated using F = G(m₁m₂)/r².

Mass and Gravity

Greater mass produces a stronger gravitational pull, as shown when a “more massive planet” increases rubber-band resistance in the class demo.

Distance and Gravity

Gravitational force decreases rapidly as distance between two objects increases (inverse-square relationship).

Weight

The gravitational force acting on an object’s mass, often measured on Earth’s surface.

Elliptical Orbit

The oval-shaped path a planet follows around the Sun, defined by its major and minor axes.

Equal Areas in Equal Times

Consequence of Kepler’s Second Law: planets move faster when closer to the Sun and slower when farther away.

Gravity Tug-of-War

Classroom activity using a rubber band to visualize how gravity varies with distance and mass.

Inverse-Square Law

A physical principle stating that a specified physical quantity is inversely proportional to the square of the distance from the source.

Gravitational Field

A region of space surrounding a mass where another mass experiences a gravitational force; weaker farther from Earth and stronger near massive objects like black holes.