### This Center(primarily titled 'Lessons On Life And The Like, After Mr. Delfin Angeles')

1. Notes on Distance and Displacement
"I took the one less traveled by." - Robert Frost
distance - length of a travelled path; without direction
displacement - how far an object is from its starting point; a quantity with definite direction

scalar quantity - has magnitude only
vector quantity - has both magnitude and direction

2. Law of Interaction

- There is no single force;
- forces act in pairs;
- 2 forces are equal in magnitude, but opposite in direction;
- they don't act on the same body.

3. Law of Momentum

In any collision, the sum of all the momenta before collision is equal to the sum of all the momenta after collision.

4. Notes on Universal Gravitation

- Any two masses in the universe attract each other with force.
- The force of gravitation between any two masses is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.

5. Notes on Relative Motion

Every thing moves. Even things at rest are moving relative to something else--the sun and the stars. For example, a book that is at rest relative to the table it rests upon moves at about 30 km/s relative to the sun and it moves even faster relative to the center of our galaxy.

GRASS
Carl Sandburg

Pile the bodies high at Austerlitz and Waterloo.
Shovel them under and let me work--
I am the grass; I cover all.

And pile them high at Gettysburg
And pile them high at Ypres and Verdun.
Shovel them under and let me work.
Two years, ten years, and the passengers ask the conductor:
What place is this?
Where are we now?

I am the grass.
Let me work.
When we discuss the motion of things, we describe motion relative to some reference point. For example, when we say a train travels at 200 km/h, we mean relative to the track. Unless stated otherwise, an object's speed is taken to be relative to the surface of the earth.

All this is theory.

(After Delfin Angeles and his notes.)