# Is there gravity on the moon?

1. Jul 6, 2009

### Pupil

2. Jul 6, 2009

Clearly that TA never took a physics course. Of course there is gravity on the moon. All objects exert their own gravitational force by virtue of the fact that they are comprised of matter.

3. Jul 6, 2009

### negitron

Yes, I believe there really are people that stupid.

4. Jul 6, 2009

### BobG

He forgot to ask the follow-up question.

If you spin a bicycle tire (on Earth) and suspend one end of the axle from a rope loop, so the tire's spin moves same direction as your curled fingers as your thumb points from the suspended end of the axle to the free side of the axle, which direction will the tire move?

a) the free end of the axle will rotate downward until the tire falls out of the rope loop.
b) the free end of the axle will rotate upward until the tire falls out of the rope loop.
c) the axle will rotate counter-clockwise around the rope loop (as you look down toward the tire)
d) the axle will rotate clockwise around the loop (as you look down toward the tire)

5. Jul 6, 2009

### arunma

Wow...clearly I haven't been hanging out with enough non-physics people.

6. Jul 6, 2009

7. Jul 6, 2009

### cristo

Staff Emeritus

8. Jul 6, 2009

### Pupil

No, I was wondering if the TA was right about the heavy boots.

9. Jul 6, 2009

### TheStatutoryApe

Since the gravitational force on the moon is weaker than on earth they may well have used weighted boots to maintain a more natural gait. Obviously this doesn't mean they would have floated away otherwise. I am also unsure if such a thing was actually done.

10. Jul 6, 2009

### AUMathTutor

...

I wonder, though, if there aren't similar misconceptions we all have about certain scientific things. I would hope that they wouldn't be this bad.

What basic, fundamental scientific knowledge should every educated person have? Can we try making posts that contain nuggets of wisdom which, once compiled, people can study in order to avoid gaffes like this? I'll go first.

11. Jul 6, 2009

### AUMathTutor

Every object with mass exerts a gravitational force on every other object with mass in the universe.

12. Jul 6, 2009

### jobyts

We had a lecturer who was very well known for her lack of knowledge on the subject. Once she was mentioning some angle between two objects is x degrees. One student wanted to make fun on her and asked a question - is it degree celsius or Fahrenheit? She got very confused and told she needs to refer and get back later.

Your TA is a genius compared to her :)

13. Jul 6, 2009

### Pupil

An objects horizontal velocity has no effect on its vertical velocity. For example, a ball dropped and a bullet fired horizontally from a gun will hit the ground at the same time (if both objects are at the same height)

14. Jul 6, 2009

### DaveC426913

No, he meant even an 8th grader should know the correct answer.

15. Jul 6, 2009

### Jimmy Snyder

Hammer, feather, moon.

16. Jul 6, 2009

### Tibarn

Not necessarily. If the gun was powerful enough, the bullet would travel far enough for the ground to curve away from it, so that the ball would actually hit the ground first.

17. Jul 6, 2009

### Proton Soup

no surprise there. the sad thing is that this may be a person planning to pursue a law degree.

18. Jul 6, 2009

### Pupil

Who said anything about a curved ground? I'm firing my gun in Flatland, where the ground is flat. If I said anything about the specifics of the planet Earth, I would have used the word tangential, not horizontal.

19. Jul 6, 2009

### Tibarn

Are you referring to the Flatland from the eponymous book, which as I recall is two-dimensional? Or perhaps Either way, if you're on a flat torus, the bullet might never hit the ground. There's also the question of whether the gravitational field is uniform. If you won't do things on Earth, at least be more specific.

20. Jul 6, 2009

### rootX

Does it matter whether objects falls or floats away on the moon surface?

But they shouldn't use things as facts for which they are ignorant IMO.

(I remember once getting into arguments with one arts teacher for something similar. I gave up :p)

21. Jul 6, 2009

### mgb_phys

Does it matter what a philosophy student thinks?

22. Jul 6, 2009

### rootX

No because they don't think anything useful.

23. Jul 6, 2009

### Staff: Mentor

I think you misunderstood what I was getting at: I realize the issue was posed to college students. I pulled the "8th grader" thing out of the air, but it is based on 8th grade being where one gets their first exposure to the concept of how gravity works. Once you know a couple of facts (gravity comes from mass, the moon has less mass than the earth), the issue becomes ridiculously simple.

I know the people polled were college students: they should be more than qualified to answer this question. Editorially, it is unfortunate, but mandatory science education in the US basically ends after 9th grade, iirc. Kids looking toward a scientific background take science classes in high school, but they aren't required. So a week or two about Newtonian physics in 8th grade might be all an American student ever sees.

I'm not sure where the disconnect lies exactly, but this issue is so simple (see the two facts required, above) that a philosophy class - where someone theoretically learns logic - should be sufficient for figuring this out.

24. Jul 6, 2009

### Proton Soup

it matters to the moon. and to the earth, too. were it to drift away a grain at a time, we would soon have no tides, no nightlight, and no signal that many species depend on for breeding.

25. Jul 6, 2009

### rootX

Restating the question for further clarification:
Does it matter "everyone knowing" whether objects falls or floats away on the moon surface?