1. AP Physics and Orbits

2. When you leave here today
You will be able to relate GRAVITATION to ENERGY now.
You can understand how orbits work and relate to energy.

3. HW
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6. What fraction of the Force does the front block have for each?
What about the back block?
How does the force of the front block on the string compare to the back block on the string?

12. Gravitational Potential Energy
Ug = mobjectgh for on a planet with gravity g
But what if we were far away, so g is different?

13. Ug = mobjectgh
Ug = mobject G∗Mplanet 𝑟 2 h where r and h are both the distance
Ug = mobject G∗Mplanet 𝑟 2 r
Ug = mobject G∗Mplanet 𝑟 but we make a change

14. Ug = mobject G∗Mplanet 𝑟
Ug = GMm 𝑟 but as height from Earth increases…U should increase
Ug = −GMm 𝑟

15. Summary of the Energy
Remember height is arbitrary… so lets call super far away ZERO energy.

23. Can you use the potential energy to figure out the velocity it is going at?
Student A: No, knowing the potential does not let you find the KE unless you know the mechanical energy at a point.
Student B: Wrong, you can set the potential energy equal to the KE since at max potential the KE is zero.

24. How fast would the satellite be going if it started from rest at that altitude and hit Earth?

25. Now to Orbits:
Look here
Idea: At slow speeds, the ball will simply fall back and hit Earth.
Idea: At the ORBITAL VELOCITY at that height, the ball will have a CIRCULAR orbit
Idea: At a velocity HIGHER than the ORBITAL VELOCITY but less than the ESCAPE VELOCITY, the ball has an ELLIPTICAL orbit
Idea: At higher velocities, it escapes Earths ‘Gravity Well’

27. Here a satellite is orbiting in an ellipse and is measured from the Earth’s center.
We want to find the velocity at the ? in terms of the variables given AND the earths mass Me.

28. Please create a table of values at R1 and R2

29. Is the work here + - or 0

30. What is the work done on the satellite here 0, + or -