Gravity Concept Inventory
Please answer the following questions about Newtonian gravity to the best of your ability. This questionnaire is for research purposes only, so your performance will NOT affect your grade in any way, and your participation is optional. Your student ID number will be used for matching your responses to other data, but your information will be destroyed after the study is over.
SELECT THE SINGLE “BEST” CHOICE
1. Besides gravity, what other factors, if any, hold us to the Earth’s surface?
a. Air pressure from the Earth’s atmosphere.
b. Forces from the Earth’s spinning motion.
c. Magnetism from the Earth’s magnetic field.
d. No other factors; gravity is the only one.
2. How would the gravitational force between the Earth and Moon differ if the Moon were twice as far
as it is now?
a. Would be the same.
b. Would decrease by less than two times.
c. Would decrease by exactly two times.
d. Would decrease by more than two times.
e. Would increase.
3. Two astronauts are floating in space far away from any planets or stars. What is the direction of the
gravitational force that they experience, if any?
a. Toward each other, because there is a gravitational force between them.
b. Away from each other because they are pulled by distant planets and stars.
c. They experience a gravitational force, but its direction cannot be determined.
d. They do not experience a gravitational force because there is no large object nearby.
4. Astronauts appear weightless in their Earth-orbiting spacecraft because…
a. They have escaped Earth’s gravity.
b. There is no air in the spacecraft.
c. They are moving at the same rate as their spacecraft.
d. The spacecraft’s rocket engines counteract gravity.
i5. The factor(s) that most affect the gravitational force between two objects are:
a. size and distance
b. mass and size
c. density and distance
d. mass and distance
e. density and size
6. Planets A, B and C are identical. A and C have a giant moon orbiting them, while B has a
lightweight artificial satellite orbiting it, as shown in the diagram. Which planet has the strongest
gravitational interaction with its satellite?
a. Planet A, because its moon is heavy and close to it.
b. Planet B, because only a lightweight object can orbit without falling down.
c. Planet C, because it can interact with a heavy object that is far away.
d. All have the same gravitational attraction, because the planets are all the same mass.
e. Not enough information to determine.
7. Why doesn’t the gravitational pull between the Sun and the planets cause the planets to fall into the
a. The background stars pull back on the planets.
b. The Sun’s magnetic fields are pushing out.
c. The speed of the planets flings them out.
d. The Sun’s rotation pushes the planets out.
8. Satellites B is three times more massive than A, but orbiting the planet at three times the distance.
Compare the force of gravity between each satellite and the planet. The diagram is not to scale.
a. A experiences a stronger force than B, because
differences in distance are more influential than
differences in mass.
b. B experiences a stronger force than A, because
differences in mass are more influential than
differences in distance.
c. A and B experience the same force, because differences
in distance are exactly compensated
by differences in mass.
d. A and B experience no force, because they are in space.
9. Assuming the Earth is perfectly round and each person is the same
mass, which person standing on Earth’s surface experiences a
stronger force of gravity?
a. Both A and D, they are near a stronger magnetic field.
b. B, he is affected by both the magnetic field and the rotation.
c. C, he is at the fastest spinning part of Earth.
d. D, he is at the bottom of Earth and could fall off.
e. All the same, they are the same distance from Earth’s center.
10. Why does the Earth exert a gravitational force on objects on its surface?
a. It has an atmosphere
b. It is so dense.
c. It has a magnetic field.
d. It has mass.
e. It rotates.
11. Suppose the Sun shrank in size but its mass remained the same so that it was compacted much ii more densely. What would happen to the size of the Earth’s orbit around the Sun?
a. Earth's orbit would shrink in size.
b. Earth's orbit would expand in size.
c. Earth would fly out of the solar system.
d. Earth's orbit would be unaffected.
12. Is there a relationship between a planet’s gravity and its atmosphere?
a. Yes, atmosphere represents a boundary where objects can experience a gravitational force.
b. Yes, atmosphere causes objects on the surface to experience a stronger gravitational force.
c. Yes, the gravitational force holds the particles in the atmosphere close to the planet.
d. No, there is no relationship between gravity and atmosphere.
13. Each planet below has the same mass M and an identical rocket orbiting at a distance D. The
darker the planet, the denser the material. Which rocket experiences a stronger force of gravity?
a. A, higher density means stronger gravity when distance to center of the planet is the
b. B, smaller distance to the surface of the planet means stronger gravity when mass of
the planet is the same.
c. Both the same, the stronger gravity from denser planets is compensated by the rocket’s
smaller distance to the surface of the planet.
d. Both the same, each planet has the same mass and the rocket is at the same distance
from the center of the planet.
e. There is not enough information given to determine.
iii14. The gravitational force between two objects is zero …
a. when another object lies in-between the two original objects.
b. when the distance between them becomes extremely large.
c. at a location halfway between the two objects.
d. when they are balanced in a stable orbit around one another.
e. when the two objects are not moving.
The following diagram shows two smaller planets of mass m and one larger planet of mass 4m, aligned
and separated by distance d between each planet. Use the diagram to answer the next 2 questions.
15. Planet A experiences a gravitational force by Planet C that is ______ that by Planet B.
a. less than
b. equal to
c. greater than
d. cannot be determined with the given information.
16. Which one of the following gravitational forces is strongest?
a. The force by Planet A on Planet B.
b. The force by Planet A on Planet C.
c. The force by Planet B on Planet C.
d. The force by Planet C on Planet A.
17. Assume that planets X and Y have the same mass, but planet X is made of a denser material, yet
planet Y is bigger. Where would a rocket that is launched from planet X begin to experience a
gravitational force from planet X that is equal to that from planet Y? The black dot shows the
halfway point for reference.
a. At point A, because planet Y is bigger.
b. At point B, because planets X and Y have the same mass.
c. At point C, because planet X is more dense.
d. The rocket does not experience a gravitational force with X or Y, because it is in space.
18. Consider an irregular-shaped asteroid of constant density shown below. Which arrow best
represents the direction of the gravitational force on the ball?
a. A, because it points to the center of mass of the asteroid.
b. B, because it points to the geometric center of the asteroid.
c. C, because it points straight down to directly below the ball.
d. D, because it points to the edge nearest the ball.
19. An astronaut standing on the Moon’s surface has a pen in his hand and releases it. What happens to
a. It falls to the surface of the Moon, but slower than on Earth.
b. It falls to the surface of the Moon, but faster than on Earth.
c. It doesn’t fall, but floats where it is.
d. It doesn’t fall, but slowly drifts away.
20. Theoretically, how far away from the Earth do you have to go to feel zero gravitational force from
a. Outside the atmosphere
b. The orbit of the Moon
c. The orbit of Mars
d. Outside the solar system
e. An infinite distance
21. Satellite B is three times more massive than Satellite A. Which satellite experiences a stronger
gravitational attraction with the Earth?
a. Neither, since they are in space.
b. Neither, they are at the same distance.
c. A, since it is easier to move.
d. B, since it has more mass.
e. Cannot be determined with the given information.
iv22. Which of the following would make you weigh half as much as you do right now?
a. Take away half of the Earth’s atmosphere.
b. Take away half of the Earth’s mass.
c. Take away half of the Earth’s magnetic field.
d. Make the Earth spin half as fast.
23. Imagine a thin tunnel that reaches to the center of the Earth. At which point (if any) would the
gravitational force between you and Earth be strongest?
a. Point A, because the gravity from the outer layers is pushing you.
b. Point B, because the gravity from the iron core is pulling you.
c. Point C, because gravity from the whole planet is pulling you.
d. The same for all points, because you have not left the planet.
24. The reason why your weight at the surface of Saturn is similar to that on Earth is that:
a. Saturn has the same mass as Earth, and your weight depends only on the planet’s mass.
b. Saturn’s large size would cause you to weigh, but the rings counter the effect.
c. Saturn is much more massive, but on its surface you are further from its center.
d. You would weigh the same on all planets in our solar system, regardless of their size.
25. Which graph best represents the gravitational force F that a rocket experiences as it travels a
distance D away from the surface of the Earth? Note that R represents the edge of the atmosphere. A
26. Which of the following is NOT primarily determined by gravity?
a. The shapes of asteroids and planets.
b. The fact that less massive objects tend to orbit more massive objects.
c. The speed at which we launch rockets from the Earth
d. The number of sunspots on the Sun.
e. The number of meteors that hit an object.
27. A person on Pluto’s surface would experience a(n) _____ gravitational force compared to on Earth.
a. Weaker, because Pluto is further from the Sun.
b. Weaker, because Pluto has less mass.
c. Equal, because both planets orbit the Sun.
d. Stronger, because Pluto’s surface is closer to its core.
28. Which one of the following statements about gravity and magnetism is true?
a. Gravity cannot exist without magnetism.
b. Gravity is not affected by magnetism.
c. Magnetism increases a planet’s gravity.
d. Magnetism cancels out a planet’s gravity.
29. Toward which part of Earth are objects on its surface pulled most?
a. The atmosphere.
b. The center point.
c. The iron core.
d. The surface.
30. A person is living on a planet where a huge hole has been carved out. Which arrow best represents
the direction of the gravitational force he experiences?
a. A, because it points along the surface with the most mass.
b. B, because it points directly to the center of mass.
c. C, because it points straight down to the center.
d. D, because it points to the hole and he would fall in.
31. In the diagram below, at which point would a spacecraft traveling from the Earth to the Moon
experience a gravitational force from the Earth that is equal to that from the Moon? Note that B is v at the halfway point.
a. A, the spacecraft is closer to Earth and Earth is more massive.
b. B, the spacecraft is exactly halfway between Earth and the Moon.
c. C, the spacecraft is further from Earth and Earth is more massive.
d. All points are the same, since the spacecraft is in space.
32. Of the objects listed at right, which experiences a gravitational force with the Earth? Sun
a. Person only Moon b. Moon and Person
c. Moon, Person, and Sun Person d. All of them
Mars e. None of them
33. Does an Earth-orbiting satellite or the Moon experience a greater force of gravity from the Earth?
a. The satellite, because it is much closer to Earth.
b. The moon, because it is much more massive.
c. They experience the same force, because they both orbit.
d. Neither experiences a force, because they are in space.
e. Not enough information given to determine.
34. How many astronomy and/or physics courses have you taken before this one?
d. more than 2
35. What is your gender?
i Adapted from E.E. Prather’s assessment. ii Adapted from a question by Philip Blanco. iii Adapted from E.E. Prather’s assessment. iv Adapted from the TOAST. v Adapted from Hudgins, D.W. & Prather, E.E. 2007, Astronomy Education Review, 5(1).