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Chapter 13

Chapter 13. Gravity. The Universal Gravity. The gravitational attraction of two objects of m 1 and m 2 is given by (magnitude only):. Example. Find the gravitational force between two people of mass m=70kg, r =0.5m away from each other. Example.

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Chapter 13

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  1. Chapter 13 Gravity

  2. The Universal Gravity The gravitational attraction of two objects of m1 and m2 is given by (magnitude only):

  3. Example Find the gravitational force between two people of mass m=70kg, r =0.5m away from each other.

  4. Example What is the gravitational force on a 1kg mass on the surface of the Earth?

  5. Weight = Fgravity

  6. Weight on the Moon Find the weight of a 1kg mass on the moon.

  7. g changes with distance

  8. Example If your weight on Earth is WE. What will your weight on the surface of a mysterious Planet X given RX = 20 REand MX = 300 ME.

  9. Orbital Motion

  10. rEM RE Calculate the Period of the Moon

  11. Satellite Find the period and tangential velocity of a satellite of mass m at distance r from the center of the Earth.

  12. Alternative Method (using v)

  13. Alternative Method (Continued)

  14. Conservation of (Total) Energy Total energy is always conserved. We will be dealing with only two kinds of energy, kinetic energy and potential energy.

  15. Gravitational Potential Energy What about PEG = mgh? PEG = mgh is only true near the planet’s surface. Far away the gravitational field gets weak and PEG = mgh is no longer true.

  16. How to derive mgh

  17. Alternatively

  18. Conservation of energy A rocket is launched vertically upward at v0= 2.1km/s. How high can it go? What is the initial KE and PE? If it reaches radial distance r, what is the final KE and PE?

  19. Conservation of energy

  20. Shoot high How fast must the launch speed be for the rocket to reach a height above the earth equal to RE.

  21. Escape Velocity What must v0 be to launch it to infinity?

  22. What you have learned • Universal gravity • Gravitation potential energy • Orbital motion • Escape velocity

  23. Physics jokes • A seminar on time travel will be given two weeks ago. • Entropy isn't what it used to be. • - Two atoms were walking across a road when one of them said, "I think I lost an electron!" "Really!" the other replied, "Are you sure?" "Yes, I 'm absolutely positive."

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