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Starter. The moon’s rotation & orbit around the Earth is 27.322 days. What is it’s period (seconds)? What does this mean to us? *hint, it has something to do with what side of the moon we see…. Announcements. Homework due tomorrow! 8 Exam next Friday, 2/7

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  1. Starter The moon’s rotation & orbit around the Earth is 27.322 days. What is it’s period (seconds)? What does this mean to us? *hint, it has something to do with what side of the moon we see….
  2. Announcements Homework due tomorrow! 8 Exam next Friday, 2/7 Toothpick Bridge, 2 weeks, 2/13 End of 4th six weeks, 2/21 I will be available: 2nd lunch today After school today (ASD room) 1st lunch tomorrow, Friday After school tomorrow * Corrections MUST be taken care of by Friday after school!

  3. Law of Universal Gravitation

  4. The “Discovery” of Gravity We’ve all heard the story… an apple fell on Newton’s head and he discovered gravity. He wondered if the force that pulled the apple down also affected the Moon.
  5. Remember Newton’s 1st Law Newton already explained how a force must be applied for an object to move in a circle. (Centripetal Force) Johannes Kepler had shown that planets and moons moved in an ellipse. Newton’s breakthrough was to explain how the same rules apply to little things like apples and big things like the moon.
  6. Gravitational Force Gravitational Force is the mutual forceof attraction between particles of matter. This force always exists betweentwo masses, regardless of what separates them. It is not just between large masses, like the sun and the Earth. It is between all objects. Not only are you pulled to the earth, but the earth is pulled to you!
  7. 1 force & 2 very different results Objects on Earth will accelerate at about 9.8 m/s2downward (we use 10 m/s2). (apple) The moon accelerates toward the Earth at 0.00272 m/s2. g moon g apple 0.00272 m/s21 = = 10 m/s2 3600 The moon is 60 times further from the center of the earth than an apple on the surface of the earth. *602 = 3600
  8. Force of Gravity Fgrav = Force of gravity ~ Proportional to…. d = distance between the 2 objects centers Fgrav ~ 1/d2
  9. Force of Gravity Fgrav= G * m1* m2 {G =6.67 * 10-11 N-m2/kg2} d2 Distance has a large effect on gravitational force The further apart, the less the force Mass of both objectsalso has an effect on the gravitational force The greater the mass, the greater the force
  10. Example #1 Find the force of gravity between a 30 kg girl and her 10 kg cat if they are 2 meters apart.
  11. Example #1 Find the force of gravity between a 30 kg girl and her 10 kg cat if they are 2 meters apart.
  12. Example #2 Find the distance between a 0.300 kg billiard ball(A) and a 0.400 kg billiard ball(B) if the magnitude of the gravitational force is 8.92 x 10-11 N.
  13. Example #2 Find the distance between a 0.300 kg billiard ball(A) and a 0.400 kg billiard ball(B) if the magnitude of the gravitational force is 8.92 x 10-11 N.
  14. What is the force of attraction between two students if the mass of one student is 40 kg, the mass of the other student is 45 kg, and the students are sitting 2.4 meters apart? What is the gravitational force of attraction between a 70kg boy and a 50kg girl if they are 0.50 meters apart? If two 4000 kg cars have a gravitational force of 1.067x10-5 N towards each other, how far apart are they? An 80.0 kg person stands 2.00 m from a 50.0 kg person sitting on a bench nearby. What is the magnitude of the gravitational force between them? What is the force of attraction between two students if the mass of one student is 48 kg, the mass of the other student is 35 kg, and the students are sitting 2.4 meters apart? SHOW WTF & CIRCLE FINAL ANSWER
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