# Aim: How can we explain Newton’s Universal Law of Gravitation? Do Now: Why does the moon orbit the Earth? You will know by the end of the lesson.

## Presentation on theme: "Aim: How can we explain Newton’s Universal Law of Gravitation? Do Now: Why does the moon orbit the Earth? You will know by the end of the lesson."— Presentation transcript:

Aim: How can we explain Newton’s Universal Law of Gravitation? Do Now: Why does the moon orbit the Earth? You will know by the end of the lesson

Gravity Gravity is a universal law. Gravity is a universal law. Should behave the same where ever you are in the universe. Should behave the same where ever you are in the universe. It's a force of attraction that exists between any two objects that have mass. It's a force of attraction that exists between any two objects that have mass.

Gravity: similar to another force of attraction Love… aww

The greater the mass, the more force of attraction The greater the mass, the more force of attraction The closer the objects, the greater the force of attraction The closer the objects, the greater the force of attraction

m 1 & m 2 = masses of 2 objects r = distance between the centers of the 2 objects What about G?

G is the Gravitational Constant What does G equal and where can we find it?

How does G compare to g? For an object on the Earth: = 9.8 m/s 2 Hence, F g = mg

Problems What is the force of attraction between two football players (m 1 = 80 kg and m 2 = 100 kg) that are standing 1 m apart? F g = 5.4 x 10 -7 N Not much attraction!

What is the force of attraction between the Earth and the Moon? F g = 2.0 x 10 20 N Now that’s a big attraction! So why doesn’t the Moon fall to the Earth?

It is falling! It also has a velocity vector tangent to the Earth What is the resultant? An orbit!

Why Doesn’t the Moon Fall Down

How is F g proportional to m 1 and m 2 ? They are directly proportional If one goes up, the other goes up

What happens to the force if: massforce double m 1 triple m 2 double m 1 and m 2 triple m 1 and m 2 ½ m 1 ½ m 1 and m 2 2F 3F 4F 9F ½ F ¼ F The trick: Start with easy numbers Manipulate Solve

How is F g proportional to r? They are indirectly proportional If one goes up, the other goes down

What happens to the force if: distanceforce double r triple r ½ r 1/3 r ¼ F 1/9 F 4F 9F

The gravitational force of attraction between two objects is 100 N. What will be the new force if you double m 1, quadruple m 2, and triple r? The force will be 8/9 F F g = (8/9)(100 N) F g = 88.9 N

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