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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. 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. Gravity: similar to another force of attraction Love… aww The greater the mass, the more force of attraction The closer the objects, the greater the force of attraction m1 & m2 = 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/s2 Hence, Fg = mg Problems What is the force of attraction between two football players (m1 = 80 kg and m2 = 100 kg) that are standing 1 m apart? Fg = 5.4 x 10-7 N Not much attraction! What is the force of attraction between the Earth and the Moon? Fg = 2.0 x 1020 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 Fg proportional to m1 and m2? They are directly proportional If one goes up, the other goes up What happens to the force if: mass force double m1 2F triple m2 3F double m1 and m2 4F triple m1 and m2 9F ½ m1 ½F ½ m1 and m2 ¼F The trick: •Start with easy numbers •Manipulate •Solve How is Fg proportional to r? They are indirectly proportional If one goes up, the other goes down What happens to the force if: distance force double r ¼F triple r 1/9 F ½r 4F 1/3 r 9F The gravitational force of attraction between two objects is 100 N. What will be the new force if you double m1, quadruple m2, and triple r? The force will be 8/9 F Fg = (8/9)(100 N) Fg = 88.9 N