6.) "The Attractive Universe"

My wife and I went to the library Wednesday night and got two books. The first is a good primer on gravitation: The Attractive Universe: Gravity and the Shape of Space by E.G. Valens. It's an excellent book filled with a broad range of information presented in a brief, interesting and simple format. It's a perfect starting point.

Gravity:

• Gravity is a natural phenomenon, (occurs naturally, not produced by humans), by which objects with mass attract one another.
• Mass, (inertial mass, we'll see later that there are other kinds), is the amount of matter an object contains. It's a measure of inertia, (an object's resistance to a change in its state of motion). It's not weight.
• Weight is a measure of the gravitational attraction for a given mass. I would weigh much less on the moon, though my mass wouldn't change, because the force of gravity on the moon is weaker.
• Inertia is an objects tendency to maintain its current velocity unless acted upon by a new force. It is an object's resistance to a change in its state of motion. Inertia is represented numerically by an object's mass.
• Gravity is an attractive Force. Forces accelerate objects.
• Acceleration: To change the movement of something: start it moving, speed it up, change it's direction, slow it down, or stop it. To overcome its inertia and change its velocity.
• Velocity: Speed in a particular direction. It is a vector quantity, like Five meters per second, west. It has magnitude and direction, as opposed to a scalar quantity, which has no direction, like five meters per second.
• Gravity is a Centripetal Force. It pulls toward the Earth's center. It's the opposite of a Centrifugal Force, which pushes outward from the center.

Calculating Average Acceleration

(A) = Average Acceleration, (V) = Change in Velocity, (T) = Time interval over which velocity changes: (A) = (V) / (T)

Calculating Average Velocity

(V) = Average Velocity, (D) = Displacement, (T) = Time:
(V) = (D) / (T)

We say "average velocity" because as an object accelerates, its velocity changes. Notice, (image at left), that the displacement of an object is not the same as the distance it may have traveled.

• Displacement is the shortest distance between where the object started and where it ended up. (Image from "Displacement (vector)" at Wikipedia: http://en.wikipedia.org/wiki/Displacement_%28vector%29)

More Research Needed: Algebra, Geometry, Physics, Mechanics: Classical and Quantum, Astrophysics, Astronomy, Logic, Statistics

My next blog entry: "Galileo Galilei".