1. Satellites and Gravitational Fields Physics 12

2. Clip of the day:  $1 000 000!  http://www.youtube.com/watch?v=- zexOIGlrFo http://www.youtube.com/watch?v=- zexOIGlrFo

3. Review questions: 1. Two balls have their centres 2.0m apart. One has a mass of 8.0kg. The other has a mass of 6.0kg. What is the gravitational attraction between them? 2. What is the speed of the moon if its mean orbital radius is 3.84x10 5 km and the mass of the Earth is 5.98x10 24 kg?  Hint: look for a convenient formula on your formula sheet!

4. Answers: 1. 8.0x10 -10 N 2. 1.02x10 3 m/s

5. Satellites

6. Alice and Bob in Wonderland  http://www.q2cfestival.com/play.php?lec ture_id=8249&talk=alice http://www.q2cfestival.com/play.php?lec ture_id=8249&talk=alice

7. Geostationary Satellite  A geostationary (or geosynchronous) satellite, will always be above the same spot on Earth  What is the orbital radius, altitude and speed of a geostationary satellite? 1. Use Newton’s Version of Kepler’s Law to solve for orbital radius  Subtract Earth’s radius from orbital radius to determine altitude 2. Set gravitational force equal to centripetal force and solve for orbital speed (or use the formula from formula sheet to solve for v!)

8. Weightlessness:  The International Space Station orbits at an altitude of 226km; determine the force of gravity on an astronaut (65.kg) at this altitude and compare this to their weight on the surface of the Earth  594N at the ISS  638N on Earth  Is the astronaut “weightless?”  NO!

9. So the what is weightlessness:  Weightlessness occurs because objects are all falling towards the surface of the Earth at the same rate  NASA simulates this on the “Vomit Comet” a high altitude aircraft that plunges toward Earth

10. Try it :  Page 591  15-17  Note: for #17 mass of sun =1.99x10 30 kg  Page 597  30-31

11. Gravitational Fields

12. Gravitational Field:  The strength of a gravitational field can be determined using a test mass  The mass should be very small compared to the mass creating the field  A gravitational field will be measured in the units of N/kg

13. Gravitational Field – One Mass:  Arrows point toward the mass showing the direction of force experienced by a mass at that point  Circles represent equal potential (i.e. where the force experienced by a mass would be equivalent

14. Gravitational Field – Two Masses:  Note that earth’s field is much larger than the moon’s  Small changes in the field as you approach the moon

15. Zero Field Intensity:  There exists a point between the earth and moon where the field intensity is zero  Determine where this position is located

17. Try it :  Page 649  15-19  Page 649  15-19