Sponge - Write Kepler’s three laws of planetary motion in your own words.

The Limits of Kepler’s

Laws

Kepler’s laws allowed the relative size of the solar system to be calculated, but not the actual size.

This could not be calculated until the invention of radar, which could be used to find the distance to Venus.

Adding these two distances, the astronomical unit is defined as 1.5 x 108 km.

Kepler’s laws told how the planets move, but not why.

Isaac Newton (1642-1727) was born in Lincolnshire, England on Christmas Day in 1642, the year Galileo died.

Newton studied at Cambridge, but the arrival of the bubonic plague forced him home for two years. He went to live on his uncle’s farm.

It was there he made one of his most famous discoveries, the Law of Gravity.

For some reason he didn’t tell anyone for 20 years, until he offhandedly mentioned it to Edmund Halley in 1684. Halley encouraged Newton to publish his work, and he did so in a work known as Newton’s Principia.

Newton’s three Laws of Motion, the Law of Gravity, and the calculus are adequate to explain all motion we see here on Earth and throughout the universe.

Newton’s First Law of Motion - objects resist acceleration. (Inertia)

Newton’s Second Law of Motion F = ma

Newton’s Third Law of Motion - To every action there is an equal and opposite reaction.

The Law of Universal Gravitation - Every particle of matter in the universe attracts every other particle with a force that is directly proportional to the product of the masses and inversely proportional to the square of the distance between them.

Galileo realized the concept of inertia (which conflicted with Aristotle’s belief that the natural state of an object was to remain at rest) long before Newton came up with his first law.

Newton’s laws show that Kepler’s First Law should be: The orbit of a planet is an ellipse, with the common center of mass of the Sun and the planet at one focus.

Escape velocity - speed required to escape our Earth’s gravitational field. This is an unbound orbit.