Gravity

If a pen is dropped on a moon, will it:

A) Float away

B) Float where it is

C) Fall to the surface of the moon

So a bunch of us TA's got together and gave our physics classes quizzes asking this question. Out of 168 people taking the quiz, 48 missed the question. The responses are below. Some people didn't write comments. The spelling and grammar were not changed, however, clarifying comments are enclosed in []'s.

Physics 324 - Modern Physics for Engineers

"A body is at rest tends to stay at rest, plus there's no gravity"

"The gravity of the moon can be said to be negligible, and also the moon's a vacuum, there is no external force on the pen. Therefore it will float where it is."

"The pen will float away because the gravitational pull of the moon, being approximately 1/6 that of the earth, will not be enough to cause the pen to fall nor remain stationary where it is. The gravatational pull of other objects would influence the pen"

Physics 222 - Second Semester Calculus-based Introductory Physics

"Because moon has gravitation 1/6 of the gravitation of earth the force will be small toward the moon [so it will float away]"

Physics 221 - First Semester Calculus-based Introductory Physics

"It will fall to the earth by force of gravity and by the attraction between the earth and the moon"

"Because the gravitational pull of the moon is much weaker than that of the earth. And object such as a pen is so lite that it will float"

"Because there are no external forces if you let go [it will float where it is]

"External forces that are present on the moon will attract the pen. There isn't gravity on the moon as there is on earth so the pen won't drop."

"Since there is no gravity it will float and fall slowly. It will not fall like in the ground quickly because there is no gravity"

"The force of gravity on the moon is a fraction of the gravity on the earth, so the moon would not be able to attract the pen to inself. Rather, it would only be able to suspend the pen"

"It will eventually fall to the surface of the moon because of the slight gravitational field plus the moment of inertia about the moon. Also with angular momentum being conserved, it must fall. I=MR^2" [We were studying conservation of angular momentum when I gave this quiz]

"The pen will fall to the surface of the moon. As we let go we will introduce some initial enerty into the pen thus putting it in a forward downward motion. Since on the moon there is no force of resistance the pen will fall very slowly towards the surface"

"If you are standing on the moon holding a pen and you let go, it will float where it is. It will not fall to the surface of the moon because a gravitational force strong enough to cause this does not exist. In addition, the pen does not have a lot of external force on it, so it will not be likely to move"

"The pen will fall to the surface of the moon because the moon generates a gravitational field by rotating and the pen must act under this force".

Physics 111 - First semester Non-calculus Physics

"It will float where it is because there is no gravity force on the moon. Also, if you just let go there isno acceleration so it should just float where it is."

"There is no gravitational force on the moon, the pen therefore has no weight so its mass has no effect on 'where it goes'. Plus, you know, there is no wind to blow the pen up there! =)"

Astronomy 150 - Physics for humanities majors

"[It will float where it is] Because there isn't a real strong gravity force on the moon. Actually it is like having none at all. If I remember right, it is only like 2.9m/s (force of gravity)"

"It will float away because the gravity of the moon won't pull it down to the surface, but it won't stay where it is because there is always some force acting on mass - (even though the gravity of the moon isn't strong enough)"

"The gravity of the earth will pull it more than that of the moon, so it will float toward earth"

"It'll float away because your body is not able to stay completely still. So it would float in the direction your hand was shaking"

"There is not much gravitational pull on the moon to have it fall to the surface. The pen is so small and light, it probably would not be affected by the gravitation of the moon so it would float away."

"There is no gravity in space so if you just let it go, it will just gently float away."

"It will float away because the gravitational force is less than here on the Earth where it would fall. I think it will float away because of what I have seen of the space rooms NASA uses to get astronauts ready for flight."

"Theoretically, it should float away because it has no mass, gravity does not pull the pen towards the surface at a great enough rate to make it fall, however it does have enough force to keep it floating and ultimately it will drift away."

"Because there is no gravity on the moon. Therefore it would float away because there is nothing to hold it there or to pull it to the surface of the moon"

"[It will float away] Because there would be no gravitational force to hold it there or make it fall to the surface of the moon"

"There is no gravitational pull on the moon to cause pen to come back towards surface. The pen would float away probably toward the gravitational pull of the earth."

"[It will float where it is] Because there is no gravitational pull. It will neither fall towards the moon because there is no gravity to pull it there nor is there any other gravitational force that will pull it away from the moon."

"Float where it is and will not move because there is no gravitational pull, it will not float away unless it is pushed."

"The gravity on the moon is such that it won't be pulled to the surface, and since the pen won't make any movement it should float where it is."

"It will float where it is until a force acts upon it. There is no gravity to act upon it."

Astronomy 120 - Physics for brain-dead

"[It will float away because there is] no gravity to hold it and no atmosphere"

"[It will float away] because the gravity on the moon is not as great as it is on the earth"

"Because the earth is a greater mass and the pen will be pulled toward the greater body because of gravity. The moon doesn't have that great of a gravitational pull"

"No gravitatational pull so it won't fall and no force pulling it away so it will float where it is"

"Lack of gravity on moon allows pen to float in space"

"Because there is no gravitational pull on the moon, there is no pull towards the moon or away from."

"The moon doesn't have gravity like the earth which would bring the pen down to the surface instead the moon's atmosphere would cause it to float above the moon's surface."

"Gravity will not pull it down, because there is less of it. It shouldn't float away just because I've never seen it happen. There's a balance between gravity and the opposite force."

"It would float where it is because gravity would not let it fall to the surface (there is no gravity) on the moon. It would not float away because it has no mass."

-- +---------------------------------------------------------------------------+ |Jonathan Partee |partee@iastate.edu | I can't spell. I know it.| |Department of *******|partee@sun2.jpl.nasa.gov | You know it. Don't hassle| |Iowa State University| | me about it. |

Here is a similar story about gravity and heavy boots on the moon.