Physics: Gravitation and Planetary Motion

A set of vocabulary flashcards covering the concepts of orbital mechanics, Kepler's laws, and Newton's Universal Law of Gravitation based on the provided lecture notes.

Centre of mass

The point inside or outside an object at which the total mass of the object can be assumed to be concentrated.

Geometrical centre

The location of the centre of mass for a spherical object having uniform density.

Centroid

The location of the centre of mass for any object having uniform density.

Centripetal force

A force acting on an object moving in a circle that is directed towards the centre of the circle, expressed as $F = \frac{m v^2}{r}$.

Kepler's first law

The orbit of a planet is an ellipse with the Sun at one of the foci.

Kepler's second law

The line joining the planet and the Sun sweeps equal areas in equal intervals of time.

Kepler's third law

The square of the period of revolution of a planet around the Sun is directly proportional to the cube of the mean distance of the planet from the Sun, such that $\frac{T^2}{r^3} = K$.

Ellipse

A curve obtained when a cone is cut by an inclined plane; it has two focal points where the sum of the distances from every point on the curve to these points is constant.

Newton's universal law of gravitation

Every object in the Universe attracts every other object with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them: $F = G \frac{m_1 m_2}{d^2}$.

Universal gravitational constant (G)

The constant of proportionality in Newton's law of gravitation; in SI units, its value is $6.673 \times 10^{-11} N m^2 kg^{-2}$.

Henry Cavendish

The scientist who first experimentally measured the value of the Universal gravitational constant ($G$).

Johannes Kepler

A German astronomer and mathematician (1571-1630) who used the observations of Tycho Brahe to discover the three laws of planetary motion.

Sir Isaac Newton

The English scientist (1642-1727) who formulated the laws of motion, the theory of gravity in his book Principia, invented calculus, and constructed the first reflecting telescope.

Calculus

A new branch of mathematics invented by Newton with wide ranging applications in physics and mathematics.

Centripetal (meaning)

A term meaning 'centre seeking,' indicating that an object moving in a circle tries to go towards the centre of the circle because of this force.