OBJECTIVE:  

1) I will be able to use Newton's formula for universal gravitational attraction to evaluate gravity between two objects after today's class.

WORDS/FORMULAE FOR TODAY:

• "G" vs "g"
• F_g = Gm₁m₂/r₂

WORK O' THE DAY: 

There are four universal forces in nature:

1. The "strong" nuclear force that binds quarks together to form protons & neutrons and also binds protons and neutrons together

2. The "weak" nuclear force force that is responsible for specific types of radioactive decay

3. The "electromagnetic" force that is characterized by the interaction between protons and electrons

4. And... GRAVITY

Gravity is a what we call an "inverse square" sorta thing...

That is to say that the strength of the force goes down by the square of the distance between two objects.

Gravity is far and away the WEAKEST of the four main forces, yet at the same time it exerts profound influences on the Universe.

• Black Holes are a region of space/time where gravity is so strong that the 'regular' laws of space and time completely break down passed a certain region (called the Event Horizon)

• The gravitational attraction between neighboring galaxies (each containing hundreds of billions of stars) tells us that most of the matter that makes up the Universe is NOT visible (hence the term Dark Energy)

• The Universe is actually accelerating outwards. By simply applying Newton's First there MUST be some sort of force accelerating the Universe OUTWARDs working against the combined gravitational attraction of all the parts. We haven't a clue what that is so we give it the clever term DARK ENERGY

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Take a look at example 13.1

Take a quick skim through section 13.2

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HOMEWORK:

 Problems #2,3,6, and 11