Copernican Model of the Solar System

Prior to Copernicus, the Earth-centered Universe of Aristotle and Ptolemy held sway on Western thinking for almost 2000 years.  In 1543, the year of his death, the Polish astronomer Nicolaus Copernicus published his book On the Revolutions of the Celestial Spheres.  In it he proposed the modern model of the solar system in which the sun was placed at the center and the Earth and other planets orbit around it.  He also proposed that the Earth, spinning on its axis, makes one rotation per day and one revolution around the sun per year.

Newton's Laws of Motion

Newton's 3 Laws of Motion

1. Every body continues in its state of rest, or of uniform motion in a [straight] line, unless it is compelled to change that state by forces impressed upon it.  (link to NASA's page on the first law)

2. Force (F) is equal to the change in momentum (m) per change in time.  For a constant mass, force equals mass times acceleration F = ma   (link to NASA's page on the second law)

3. For every action there is an equal and opposite reaction.

Here is a link to NASA's most excellent website which does a great job of explaining the 3 laws to the layperson.