Hacker Newsnew | past | comments | ask | show | jobs | submitlogin

One explanation for the wrong answers is how people use the phrase 'pen floats', and how people are imprecise about using words.

The gravitational constant is 1/6 of the Earth's. This means that I can jump on the Moon 6 times higher than here and the pen will tale 6 times longer to fall down.

It will take 6 times longer for gravity to 'kick-in' and cause the perceivable movement, as we got used to here on Earth - where on Earth the pen moved already 6 cm on the Moon the movement is still 1 cm.

It looks as if the things are moving slower. I can catch a falling egg before it reaches the ground, my reactions are like of a fly on Earth.

So I can say that the things are floating on Moon, because they are not accelerating and falling fast enough, in common terms. In interstellar space the pen will fall onto the neighbor galaxy, but will do this so slow, that I will perceive as if it is floating. If the pen will move alongside with an object much smaller than the Moon (a rock), the pen will fall onto the rock with much slower acceleration. For time perception of humans it will float in space.

Another explanation for wrong answers is that if you feed people with stupid questions, you will get stupid answers. Have you asked me to answer these questions I will surely answer wrongly 'pen floats' and 'heavy boots' on purpose only to prove the point. These answers seem to be serious enough to mislead you.



No, it does not take the pen 6 times longer to fall down on the Moon compared to Earth. Not even close. That's not how acceleration works. [I can give the equation, but I think it's more instructive if people think about it themselves :-) ]

Also, actually try dropping a pen, like right now. Gravity "kicks in" immediately - there's no perceptible delay. (Unless your perception is way different from mine.)


I suspected that time difference between falls would be not linear, but I was not sure about actual ratio.

Playing with freefall distance equations showed that time to fall difference is square root of 6. Here we are:

  Height = gEarth*timeOnEarth^2/2 = gMoon*timeOnMoon^2/2
  gEarth = gMoon * 6
  6 * gMoon * timeOnEarth^2/2 = gMoon * timeOnMoon^2/2
  6 * timeOnEarth^2 = timeOnMoon^2
  timeOnMoon = sqrt(6 * timeOnEarth^2)
  timeOnMoon = sqrt(6) * timeOnEarth = 2.45 * timeOnEarth


The gravitational constant is constant DUH! It's worth the same 6.67384 × 10-11 m3 kg-1 s-2 on the Moon than on Earth than in the other corner of the Universe! (AFAWCK for the other corner of the Universe, from the kind of stellar light we get from there).


Thanks, you caught me in my incompetency. The standard gravity on Moon it supposed to be.




Guidelines | FAQ | Lists | API | Security | Legal | Apply to YC | Contact

Search: