Kepler's Laws of Planetary Motion

This page delves into the three laws of planetary motion discovered by Johannes Kepler, which are fundamental to understanding the Mouvement dans un champ de gravitation.

Definition: Kepler's First Law (Law of Ellipses): In a heliocentric reference frame, planets orbit the Sun in elliptical paths with the Sun at one focus of the ellipse.

A diagram illustrates the elliptical orbit, showing the semi-major axis (a) and semi-minor axis (b).

Definition: Kepler's Second Law (Law of Equal Areas): The line segment joining a planet to the Sun sweeps out equal areas in equal time intervals.

This law implies that planets move faster when they are closer to the Sun in their orbit.

Definition: Kepler's Third Law (Law of Periods): The ratio of the square of a planet's orbital period to the cube of its semi-major axis is constant for all planets in the solar system.

The mathematical formulation of the third law is given as:

Formula: T² / a³ = constant (in units of s²/m³)

For nearly circular orbits, the radius r can be approximated as the semi-major axis a. The document then derives the period for a circular orbit:

Example: T = 2πr / v = 2π √(r³ / GM)

This leads to the more general form of Kepler's Third Law:

Formula: 4π² / (GM) = T² / r³ = constant

These laws are essential for solving problems in Exercices corrigés loi de Kepler PDF and understanding the Mouvement des satellites et des planètes Terminale S exercices.