1. Orbits Tides

2. Announcement Next week is a short week – Fall Break! There is no school on Thursday or Friday next week We do have class on Monday and Wednesday, but no lab next week

3. Bound and unbound orbits: But Newton;s Laws also “extend” Kepler’s Laws… Newton’s Law of Gravity and Laws of Motion lead to a variety of possible orbital shapes “Conic Sections” Newton’s laws lead directly to, or “explain”, ALL of Kepler’s Laws of Planetary Motion In math these are known as “conic sections”

4. Is it possible for a large man to teeter-totter with a small child? A) No. They have to have the same weight to balance. B) Yes, but only if they are the same distance from the balance point. C) Yes, but only if the child is closer to the balance point. D) Yes, but only if the man is closer to the balance point. E) No. Newton’s laws make it clear that they can’t possibly balance.

5. Is it possible for a large man to teeter-totter with a small child? A) No. They must have the same weight to balance. B) Yes, but only if they are the same distance from the balance point. C) Yes, but only if the child is closer to the balance point. D) Yes, but only if the man is closer to the balance point. E) No. Newton’s laws make it clear that they can’t possibly balance.

6. Newton’s Laws make it clear that objects orbit their common center of mass Two stars of equal mass A large star and a small star A star and a large planet

7. Center of Mass The Earth and Moon both move in circles around their common center of mass. The official term is “barycenter”

8. Objects orbit their common center of mass Newton derived a version of Kepler’s 3 rd Law that involves the masses of the two bodies. This will allow us to determine the masses of planets, stars, black holes, etc., by observing objects orbiting them! Newton’s version of Kepler’s 3 rd Law

9. It’s used to calculate the total mass of two orbiting bodies… Newton’s version of Kepler’s 3 rd Law a is the average distance between the bodies  in meters p is the period of the orbit  in seconds

10. a is the average distance between the bodies  in meters p is the period of the orbit  in seconds Example: Use the orbit of Mercury to calculate the mass of the Sun.

11. Orbital Energy Low kinetic energy High potential energy High kinetic energy Low potential energy Total energy remains the same throughout the orbit

12. Orbital Energy Higher orbits have higher total energy To change orbits, the energy of the satellite must be changed Adding energy raises the satellite to a higher orbit

13. Is it possible to add enough energy to a satellite that it will never come back? A) Yes B) No, gravity will ultimately pull all objects back to Earth. C) It depends on the mass of the satellite.

14. Orbital Energy Escape speed or Escape “Velocity” You CAN add so much energy that the satellite never comes back!

15. Example: What is the escape speed from the surface of the Earth? (Yes, we’re ignoring air resistance.)

16. Example: What is the escape velocity for Earth, starting from the orbital distance of the Moon?

17. Tides

18. The gravity of the Moon causes “tidal bulges” on Earth. Both the solid Earth and the oceans bulge, but the ocean bulge is most obvious. The ocean bulge, along with the rotation of the Earth, cause two high tides every day.

19. The Sun also creates tidal bulges on Earth, though not as extreme. Spring tides Sun and Moon align, so their tidal bulges add, creating more extreme tides New Moon and Full Moon Neap tides Sun and Moon are at right angles, so their tidal bulges cancel each other a bit, creating less extreme tides 1 st and 3 rd quarters

20. The tidal bulge is actually a little east of the Moon, due to drag and the Earth’s rotation.

21. The Moon’s gravity acts on the “Center of Gravity” of the Earth. This is a “backwards” pull, slowing the Earth’s rotation. The Earth pulls forward on the Moon (Newton’s 3 rd Law), speeding it up, and causing it to drift away from Earth a few centimeters each year. Center of gravity Moon’s pull on Earth’s Center of gravity

22. How many low tides does a coastal city experience every day? A) 1 B) 2 C) 3 D) 4

23. Astro-Cash Cab! Alex Adams Tabitha Richardson Miranda Glowczewski Marc Ramirez Alejandro Torres

24. 1) Compared to a smaller planet, a LARGER planet of the SAME mass would have an escape speed that is… A.The same. B.Higher. C.Lower. D.It depends on what the planet is made of.

25. 2) True or False ? The Earth actually wobbles once per month as it and the Moon orbit their barycenter.

26. 3) What is the name for the more extreme tides that occur when the Sun’s and Moon’s gravity work together?

27. 4) At which of the following Moon phases do neap tides occur? New Moon 1st quarter Waning gibbous Full Moon Waxing crescent