That is an unfair characterisation, I think. The article does indeed reproduce heavyboots in its 725 words entirety (according to pages's word count for what that one's worth), but tacks a further 930 words afterwards. And these 930 are interesting indeed as they're further explorations of the phenomenon and discussion on its underlying reasons.
Fair enough - I've changed the wording a bit. Personally, though, I thought that the follow-on discussion didn't add much beyond what was mentioned in the original heavyboots article.
This was a pretty entertaining read. First I thought I would sense a smug sense of superiority of natural science over the humanities, but then I realized he performed the same test on his physics students.
I always sucked in tests. In the first question, I would have hesitated between b) and d).
The reason for choosing b) would have been that the moon's gravity being weak, the earth's gravity nullified the moon's thus having a floating pen.
The reason for choosing d) would be because Moon's gravity is stronger than Earth's.
This is why I think tests are stupids. If I had chosen b) instead of d) I would have gotten a wrong answer. Even though my thought process would be correct. Just missing the right information (which could have been easily found outside a test environment).
The relative strength of gravity mostly does not matter. If the Earth pulled on you harder than the moon, you'd still fall towards the moon, because the moon is just as strongly affected by that gravity as you are (momentarily ignoring tides).
So no, I'm pretty sure your thought process wasn't remotely correct.
His thought process is correct, but his "pen on the Moon" model is missing vital element (that Moon is in free fall/orbiting Earth).
If Moon was hanging on a stick connected to Earth (instead of orbiting Earth) and Earth gravity forces on a pen were stronger than Moon's gravity forces, then pen would fall in Earth.
Of course you and I know that there are no such strong materials for that Earth-Moon stick, but that's yet another level of complexity that most people don't have to know about.
>If Moon was hanging on a stick connected to Earth (instead of orbiting Earth) and Earth gravity forces on a pen were stronger than Moon's gravity forces, then pen would fall in Earth.
Technically that's true, but it would require a completely different scenario. Earth's gravity is miniscule at that altitude. For the moon to have a weaker force it would have to be so small that it would likely not even qualify as a moon any more.
Well, you are ignoring tides, I'm not. I say that theoretically, you could be at the Roche Limit, and then the pen would stay still. Hypothetical, yet real. So thank you very much but yeah, the thought process stand correct.
Tides are purely about relative differences in gravity between positions, though, not about differences in pull between two bodies. You can still be at a point where the Earth's gravity is greater than the Moon's while on the surface of the Moon without anything floating away and while comfortably outside the Roche limit. In fact, such a situation must necessarily exist outside the Roche limit for any body.
I'd be comfortable marking you wrong, unless you had a reason to think the two forces would be almost exactly the same on the moon's surface. It's not a matter of being confused as to which is stronger when you say 'neither'.
Thanks for posting that. Not one to complain about blogspam, but that's one of the all-time great "internet motherfucker" posts. Neither Sciencegeekgirl.com (lol, brand yourself harder) nor anyone else can do much to add to it.
Actually, Sciencegeekgirl.com adds VERY MUCH to the article, namely a highly interesting discussion of WHY students give these wrong answers. No, it's not because they're stupid or ignorant.
Obviously, anyone who answers a question incorrectly is ignorant of the correct answer, but the point is that in many cases the wrong answer seems to be logically based on a wrong mental model of how gravity works. Just like Aristotelian physics. And Newtonian physics as well. Would you call Aristotle and Newton ignorant?
The interesting part is the discussion of what these wrong mental models look like and how you can teach a correct one.
Absolutely. There was much they did not know, as is true of anyone. "Ignorant" is not an insult, it simply means you do not know something. Would you say Aristotle and Newton knew everything about everything? If not, then they would be, by definition, ignorant of the things they did not know.
The problem is that they may know that the Moon has gravity, but they don't understand what that concretely means when it comes to questions like this.
I would dispute the validity of calling that state of mind "knowing that the moon has gravity". I would instead call it "memorized a couple of correlated keywords".
On its own yes, but if combined with the previous statement that a pen would float away, it just exhibits a piecemeal and inconsistent understanding of physics.
Oh god. Feathers and dust don't float away because they're weightless.
They float away because air currents exert forces on them that are greater than their weight. Eventually, in a still-air environment, the feather and the dust will settle to the ground. You can verify this by going to your nearest attic.
A significant part of the article is a reposting of http://www.phys.ufl.edu/~det/phy2060/heavyboots.html
Edit: Changed wording re how much of article is repost