3 ms·

> the nail would reach escape velocity and never come back down to earth See https://en.wikipedia.org/wiki/Impact_depth https://en.wikipedia.org/wiki/Impact_de

by bloak 5y ago

> the nail would reach escape velocity and never come back down to earth See https://en.wikipedia.org/wiki/Impact_depth https://en.wikipedia.org/wiki/Impact_depth I am not a physicist, but iron is about 6500 times denser than air so that suggests that a 5 cm nail would reach a height of very roughly about 300 metres, assuming you fired it upwards with sufficient speed, it remained parallel to the direction of flight, and it didn't melt or burn. You should definitely allow more space that that if you're thinking about filming the experiment from a helicopter over your magnet lab, but I would guess that even Nine Inch Nails wouldn't be hitting any satellites. EDIT: OK, that impact depth formula is only applicable to projectiles travelling faster than the speed of sound in the medium, which is about 300 m/s. But without air resistance an object fired upwards at 300 m/s reaches a height of about 4500 metres! There's a big gap between those two rough approximations, so if someone wants a more accurate answer I suppose they will just have to look up the actual formulae for actual air resistance.

bananabreakfast 5y ago
Interesting point. Although, a 5cm nail is tiny, that's like what you'd use to hang a picture on the wall. A real carpenter's nail is what I was picturing and that's more like 10-15cm which 2-3x's your impact depth (which is still only ~1km). So I think if anything, your point is basically proof that a nail or any traditional gauss gun projectile would absolutely ablate into gas immediately when fired at the hypersonic speed of orbital escape velocity.
- jjk166 5y ago
  Yeah, that's why the "rod's from god" idea for an orbit to ground kinetic weapon (which is the same problem just in reverse) used tungsten rods the size of telephone poles, and even those would slow down by 5 km/s as they pass through the atmosphere.

by bloak 5y ago

bananabreakfast 5y ago

Interesting point. Although, a 5cm nail is tiny, that's like what you'd use to hang a picture on the wall. A real carpenter's nail is what I was picturing and that's more like 10-15cm which 2-3x's your impact depth (which is still only ~1km). So I think if anything, your point is basically proof that a nail or any traditional gauss gun projectile would absolutely ablate into gas immediately when fired at the hypersonic speed of orbital escape velocity.

jjk166 5y ago
Yeah, that's why the "rod's from god" idea for an orbit to ground kinetic weapon (which is the same problem just in reverse) used tungsten rods the size of telephone poles, and even those would slow down by 5 km/s as they pass through the atmosphere.