1. Gravitation Created by Craig Smiley (Harrison HS, West Lafayette, IN)
Supported by grant PHY
from the National Science Foundation
and by Purdue University

2. Gravitation
If you used a rocket pack to fly to a height equal to Mars’ radius above the surface of Mars, what would happen to your weight? (ignore the weight of the rocket pack)
Decrease to a 1/4 of your weight
Decrease to a 1/2 of your weight
Stay the same
Increase by 2x your weight
Increase by 4x your weight
You would be weightless

3. Orbits
What would need to happen to maintain Earth’s circular orbit around the Sun if the Earth’s mass suddenly increased?
Increase Earth’s radius
Increase Earth’s orbiting speed
Increase Sun’s mass
Decrease the distance between Earth and Sun
Nothing would have to change

4. Orbits
What would need to happen to the Earth to maintain a circular orbit if Sun’s mass decreased?
Distance from Sun ↑ or Earth’s speed ↑
Distance from Sun ↑ or Earth’s speed ↓
Distance from Sun ↓ or Earth’s speed ↑
Distance from Sun ↓ or Earth’s speed ↓
None of these

5. Orbits
Assuming all the planets have circular orbits around the Sun, what happens to the planets’ period of revolution (time around the Sun) as you get farther away from the sun
Get shorter
Get longer
Stay the same
Can’t be determined without the mass of the planet

6. Orbits
Assuming all the planets have circular orbits around the Sun, what happens to the planets’ period of revolution (time around the Sun) as you get farther away from the sun
Get shorter
Get longer
Stay the same
Can’t be determined without the mass of the planet

7. Circular Orbits
What would need to happen to maintain Earth’s circular orbit around the Sun if the Earth’s mass suddenly increased?
Increase Earth’s radius
Increase Earth’s orbiting speed
Increase Sun’s mass
Decrease the distance between Earth and Sun
Nothing would have to change

8. Circular Orbits
The Sun’s mass doubled. What would need to happen to the Earth’s distance from the center of the Sun to maintain a circular orbit moving at its original speed?
4r D. r 2
2r E. r 2
2r F. r 4

9. Circular Orbits
The Sun’s mass is halved. What would need to happen to the Earth’s speed to maintain a circular orbit moving at its original distance from the center of the Sun ?
4v D. v 2
2v E. v 2
2v F. v 4

10. Suppose the Sun were to collapse into a black hole (shrinks radius, but maintains the same mass). What effect would this have on the Earth’s orbit?
A. The size of the orbit would decrease and the orbital period would decrease.
B. The size of the orbit would increase and the orbital period would increase.
C. The size of the orbit and the orbital period would remain unchanged.
D. none of these
Answer: C

11. Circular Orbits
Assuming all the planets have circular orbits around the Sun, what happens to the planets’ period of revolution (time around the Sun) as you get farther away from the sun
Get shorter
Get longer
Stay the same
Can’t be determined without the mass of the planet

12. The planet Saturn has 100 times the mass of the Earth and is 10 times more distant from the Sun than the Earth is (assume it also has a circular orbit).
Compared to the Earth’s acceleration as it orbits the Sun, the acceleration of Saturn as it orbits the Sun is
A. 100 times greater.
B. 10 times greater.
C. the same.
D. 1/10 as great.
E. 1/100 as great.
Answer: E

13. Apparent Weight
While the space-shuttle orbits the Earth the astronauts appear to be weightless:
There is no gravity above the atmosphere
The force of gravity is much weaker when they are that far away from the Earth
They are constantly “falling” around the Earth
None of these

14. Apparent Weight
Show Vomit Comet Video
Why were they floating inside the plane?
They went high enough so there was very little gravity acting on them.
The plane was accelerating downward at 9.8m/s2 so they were “falling” while inside the plane.
They had powerful magnets in the plane, but in order for them to work they needed to be off the ground.
None of these.

15. An astronaut is floating around in the
space shuttle's cabin. What is her
acceleration, as measured from the
earth's surface?
zero - she's floating
very small, directed towards the center of the earth
very small, directed along the line of travel of the shuttle
quite large, nearly g, directed towards the center of the earth
quite large, nearly g, directed along the line of travel of the shuttle

16. Gravitational Potential Energy

17. A. does positive work on the satellite.
A satellite is moving around the Earth in a circular orbit. Over the course of an orbit, the Earth’s gravitational force
A. does positive work on the satellite.
B. does negative work on the satellite.
C. does positive work on the satellite during part of the orbit and negative work on the satellite during the other part.
D. does zero work on the satellite at all points in the orbit.
Answer: D

18. Dropping a rock from r = ∞
If there was nothing else in the universe except the Earth and a rock, and the rock was taken to r = ∞ away and released from rest, how fast would it be going by the time it fell that far before hitting the Earth?
Infinitely fast
Speed of light, b/c nothing that go faster than the speed of light
A little slower than the speed of light because it has mass
Significantly slower than the speed of light

19. Gravitational Equipotential Lines
What happens to gravitational potential energy if you move an object with mass from a lower value equipotential line to a higher value equipotential line?
increases
decreases
stays the same
60m
50m
40m
30m
20m
10m 0m
600 J/kg
500 J/kg
400 J/kg
300 J/kg
200 J/kg
100 J/kg
0 J/kg
height (m) above ground zero
gravitational potential
(g = 10m/s2)

20. Gravitational Equipotential Lines
What is the sign for Work done by gravity if you move an object with mass from a lower value equipotential line to a higher value equipotential line? + –
60m
50m
40m
30m
20m
10m 0m
600 J/kg
500 J/kg
400 J/kg
300 J/kg
200 J/kg
100 J/kg
0 J/kg
height (m) above ground zero
gravitational potential
(g = 10m/s2)

21. Gravitational Equipotential Lines
What is the sign for Work done by gravity if you move an object with mass from a lower value equipotential line to a higher value equipotential line and then back to the initial lower value equipotential line? + –
60m
50m
40m
30m
20m
10m 0m
600 J/kg
500 J/kg
400 J/kg
300 J/kg
200 J/kg
100 J/kg
0 J/kg
height (m) above ground zero
gravitational potential
(g = 10m/s2)

22. Gravitational Equipotential Lines
What is the sign for Work done by gravity if you move an object with mass around an equipotential line? + –

23. Gravitational Equipotential Lines
What happens to gravitational potential energy if you move an object with mass from a lower value equipotential line to a higher value equipotential line?
increases
decreases
stays the same

24. Gravitational Equipotential Lines
What is the sign for Work done by gravity if you move an object with mass from a lower value equipotential line to a higher value equipotential line? + –

25. Gravitational Equipotential Lines
What is the sign for Work done by gravity if you move an object with mass from a lower value equipotential line to a higher value equipotential line and then back to the initial lower value equipotential line? + –