Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: paul.fr on 29/12/2007 17:00:06

Title: dropping a coin down the stairs.
Post by: paul.fr on 29/12/2007 17:00:06
at work we have a 6 storey flight of stairs, with a nice gap going all the way down. no matter how hard i try to drop a coin from the top to the bottom, it never falls straight, always drifts to one side or the other.
why can i not drop the coin straight down the middle of the stair well?
Title: dropping a coin down the stairs.
Post by: lightarrow on 29/12/2007 17:13:26
Quote from: paul.fr on 29/12/2007 17:00:06
at work we have a 6 storey flight of stairs, with a nice gap going all the way down. no matter how hard i try to drop a coin from the top to the bottom, it never falls straight, always drifts to one side or the other.
why can i not drop the coin straight down the middle of the stair well?
Aerodynamics/wing effect. When you drop the coin, even extremely weak air perturbations at the coin make it deflect a little; I suppose that then the aerodynamic forces make it keep that deflection.
Title: dropping a coin down the stairs.
Post by: neilep on 29/12/2007 18:08:31
Could it just be that the stair well is not completely perpendicular ? [;)]
Title: dropping a coin down the stairs.
Post by: lightarrow on 30/12/2007 12:32:20
Quote from: neilep on 29/12/2007 18:08:31
Could it just be that the stair well is not completely perpendicular ? [;)]
I assume that's the case of the Pisa Tower, for example   [;)]
Title: dropping a coin down the stairs.
Post by: neilep on 30/12/2007 14:47:51
Quote from: lightarrow on 30/12/2007 12:32:20
Quote from: neilep on 29/12/2007 18:08:31
Could it just be that the stair well is not completely perpendicular ? [;)]
I assume that's the case of the Pisa Tower, for example   [;)]

Yes yes...the tower of Pisa....right beside Pisa Airport in my favourite country...Italy....YAYYYYYYYYYYYYYYY !!!!
Title: dropping a coin down the stairs.
Post by: Soul Surfer on 30/12/2007 17:03:59
You can see the effect better if you drop a coin vertically into deep water.  The fluid dynamical effects will cause the coin to flip one way and move to the side and then change its attack angle and move back again in an oscillatory motion.
Title: dropping a coin down the stairs.
Post by: lyner on 30/12/2007 17:52:51
stick the coin to a length of light thread and hang it until it stops swinging. burn the thread non-contact with a match flame.
if your stairs are not in Pisa, your coin will have the best chance of making it.
Title: dropping a coin down the stairs.
Post by: that mad man on 30/12/2007 18:49:05
Sorry sophiecentaur I don't think that can be quite right.

The main reason why a coin tossed or dropped from a high place never reaches a high enough terminal velocity to hurt is because of the drift. Its not a round item, fairly flat and easily upset by air drag/friction.

In a vacuum it would go straight.
Title: dropping a coin down the stairs.
Post by: lyner on 31/12/2007 18:05:25
I did say it would have the best chance. i.e. eliminating  the main factor on release. What it does after it has a high speed is another matter.
How fast would you suggest it would need to be falling before the aerodynamics would be significant? Would that speed be after one storey or ten?
This a typical NS topic; very open ended.. How wide is the gap and how high is the building AND which coin?
Title: dropping a coin down the stairs.
Post by: that mad man on 31/12/2007 20:51:29
Paul did mention that it was a flight of 6 stairs so I presumed fairly high.

2 flights per floor on average = 3 floors

At a guess, distance between floors = 3mt

So a total drop of around 9mt

But, he didn't mention which coin.. [;)]


Now, I hope you have a wonderful holiday and new years eve. [:)]

Title: dropping a coin down the stairs.
Post by: lyner on 01/01/2008 00:11:56
happy new year and avoid any falling coins. stick to banknotes.
Title: dropping a coin down the stairs.
Post by: syhprum on 01/01/2008 12:49:03
If you enclosed the stairwell and pumped out all the air to distinguish which deviation from a straight drop was caused by aerodynamics and which by initial instability your neighbours would probably be mean spirited enough to complain.
Title: dropping a coin down the stairs.
Post by: paul.fr on 01/01/2008 17:05:44
Quote from: sophiecentaur on 31/12/2007 18:05:25
I did say it would have the best chance. i.e. eliminating  the main factor on release. What it does after it has a high speed is another matter.
How fast would you suggest it would need to be falling before the aerodynamics would be significant? Would that speed be after one storey or ten?
This a typical NS topic; very open ended.. How wide is the gap and how high is the building AND which coin?

jeez, you would think this was a science forum or something where facts and such were handy.

I will post some figures later, Happy new year to you all, and welcome back Bee.
Title: dropping a coin down the stairs.
Post by: paul.fr on 01/01/2008 17:06:58
Quote from: sophiecentaur on 01/01/2008 00:11:56
happy new year and avoid any falling coins. stick to banknotes.

See the difference? I throw 2 and 10p coins, Andrew throws £ notes! Spare some change guv.
happy new year Andrew.
Title: dropping a coin down the stairs.
Post by: lyner on 01/01/2008 21:40:04
POUND NOTES ??
when did you last leave a tip in a restaurant?