How did Kepler develop his second law of motion

Answer 1

Johannes Kepler developed his second law of motion, also known as the law of equal areas, by observing and analyzing the motion of planets in our solar system.

Kepler started his observations with Mars, as it was the most challenging planet to track due to its complex motion. He first gathered a large amount of data on Mars' position in the sky over a long period of time.

Kepler then noticed that the speed of Mars in its orbit around the Sun was not constant. Sometimes it moved faster, and other times it moved slower. This contradicted the prevailing belief at the time that the planets moved at a uniform speed in circular orbits.

To make sense of this, Kepler investigated whether there was a relationship between the distance of the planet from the Sun and the speed at which it moved. He concluded that there was indeed a connection.

Through his calculations, Kepler realized that a planet moves faster when it is closer to the Sun in its orbit and slower when it is farther away. In other words, the area swept out by the planet as it travels in its orbit is always the same in equal time intervals.

Kepler formulated this as his second law of planetary motion: "A line joining a planet and the Sun sweeps out equal areas in equal times."

This law not only described the varying speeds of the planets but also provided a more accurate model of their orbits. Instead of moving in perfect circles, as previously believed, Kepler's second law showed that planets move in elliptical orbits, with the Sun at one of the foci.

Kepler's second law was published in his work "Astronomia Nova" in 1609, which also included his first law of planetary motion, describing the shape of planetary orbits. The combined three laws formed the foundation for Isaac Newton's later work on the laws of motion and universal gravitation.