Universal Laws

When you think about it, everything has rules, from the smallest atoms to the universe itself. Some of the main rules that govern our very existence (whether or not they are evident in our daily life) are gravity, Newton’s Laws of Motion, and Kepler’s Laws of Planetary Motion.

A force is defined as any push or pull on an object, and gravity is perhaps the supreme force: anything that has mass exerts a gravitational pull. Gravity was the guiding hand behind the formation of our solar system, according to solar nebula theory. This hypothesis states that, after the star of whose guts we are made exploded, gaseous clouds coalesced around a central mass that was to become our sun. The sun’s gravity caused it and the surrounding protoplanets to spin, and our earth’s orbit has continued to this day.

The iconic image of Sir Isaac Newton catnapping against a tree shortly before an apple fell on his head and sparked his “discovery” of gravity may not be entirely accurate, but he did an excellent job of summarizing this unseen, mysterious force. Newton’s first law, the Law of Inertia, states that “An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.” This is easily demonstrated: take an stationary object--a soccer ball, perhaps. When placed on a field, the ball does not move: gravity pulls down on the ball, but the ground pushes back with equal force. The second law says that “The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object,” which is often transcribed, more comprehensibly, as a=Fnet / m, or Fnet=m×a. This is clear in that the same amount of force applied to two objects, one large and one small, will produce a greater  acceleration in the smaller object. Newton’s third law says that “For every action, there is an equal and opposite reaction.” Picture two people leaning on one another. The forces each of them is exerting on the other are balanced. Now (in your mind) replace one of the people with a brick wall. Although it may not be obvious, the forces are still in balance, and the force the person exerts on the wall is equalled in the wall’s resistance to it.

In close relation to Newton’s Laws are Kepler’s Laws, which deal with motion on a somewhat larger (but more fixed) scale: the scale at which the planets in our solar system revolve. Kepler’s first law is the Law of Ellipses, which explains that planets orbit the sun on a path in the shape of an ellipsis, a special figure formed that the sum of the distance from any one point to two foci is the same. In simpler terms, the planets’ orbits are oval-shaped. The second law is the Law of Equal Areas, stating that, though a planet’s speed fluctuates depending on its distance from the sun, if imaginary lines are drawn from the planet to the sun at regularly spaced intervals in time, the figures formed will have the same area. Kepler’s last law is more numerical in nature. His Law of Harmonies, a comparison between the orbit period and orbital radius of a planet, shows that the ratio of the squares of the periods to the cubes of their average distances from the sun is the same for every one of the planets.