The Laws of Planetary Motion
The German mathematician Johannes Kepler (1571-1630) was the first person to show that the planets move around the Sun in elliptical orbits. He was originally an assistant to Tycho Brahe and his work was based on Tycho's observations. Kepler devised three important laws of planetary motion that are still in use today:
1. The motion of a planet around the Sun describes an ellipse, with the Sun at one of the foci (i.e. centers).
2. A line joining the center of the Sun with the center of a planet sweeps out equal areas in equal times.
3. The square of a planet's orbital period is proportional to the cube of its mean distance from the Sun.
Newton's Laws of Motion
Isaac Newton (1642-1727)
1. A body will remain at rest or travelling in a straight line at constant speed unless it is acted upon by an external force.
2. The resultant force exerted on a body is directly proportional to the acceleration produced by the force.
3. To every action there is an equal and opposite reaction.
The Laws of Thermodynamics
Thermodynamics is the study of the relationship between heat and mechanical energy and the conversion of one into the other.
1. The Law of the Conservation of Energy
Energy cannot be created or destroyed. It can only change, or be converted from one form to another.
2. The Law of Entropy
Entropy cannot lesson. Heat cannot flow from a cold source to a hot source, but always dissipates from a hot source, so certain processes can only occur in one direction: from order to disorder. In other words, the universe must be progressing towards greater entropy and disorder rather than the reverse or, at least the entropy of the universe does not decrease.