The formulation of physical laws from the generalization of the phenomena: physical laws are the way nature usually behaves based on what has been observed in the past.

Three basic laws of planetary motion:

1. The orbit of a planet is an ellipse, with the sun at one focus.
2. The line joining the position of a planet in its orbit to the sun (the radius vector) sweeps out equal areas in equal times.
3. The squares of the orbital periods of the planets are proportional to the cube of their mean distances from the sun.

Sir Isaac Newton (1642-1727) is given credit for determining how the forces of gravity controls the movement of the planets.

Newton's three laws which explain how forces make everything move

1. Newton's first law, "an object that isn't being pushed or pulled by a force either stays still or keeps moving in a straight line at a constant speed."

It is usually not obvious that a moving object will keep moving because objects are almost always being hindered by forces; such as, friction and gravity. When a car loses traction on a wet or icy road; friction is much weaker and the car will glide along in a straight line, thus showing Newton's first law at work.

2. Newton's second law, "forces make things accelerate and the bigger the force, and the lighter the object, the greater the acceleration."

   "Acceleration" means going faster, but to a scientist it can mean three things: speeding up, slowing down (negative acceleration), or changing direction. This means that lighweight things need less force to move than heavy things and that is why small sports cars have better acceleration than big trucks.

3. Newton's third law, "every action has an equal and opposite reaction."

   "Actions" or forces always come in opposite pairs; so, the third law explains how rocket engines work: engines push burning gases out backward with a powerful force and an equal and opposite force pushes the rocket-car forward.