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A question for the Physics/Engineers
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Author:  billrogers [ Fri Dec 10, 2010 12:09 pm ]
Post subject:  A question for the Physics/Engineers
Does a wheel... (rim, tyre and tube) At say 60psi pressure have better boyance than the same at say 10 psi.
Boyancy being flotation in water..
Regards Bill
Author:  atari4x4 [ Fri Dec 10, 2010 12:11 pm ]
Post subject:  Re: A question for the Physics/Engineers
i know nothing about Physics/Engineering, but i'd say no as it's still dispersing the same volume of water no mater what psi.
Author:  sbbunno [ Fri Dec 10, 2010 12:17 pm ]
Post subject:  Re: A question for the Physics/Engineers
would'nt it be heavier as (no matter how little) more air compressed into a small area making it denser?
maybe lol
Author:  Che [ Fri Dec 10, 2010 12:18 pm ]
Post subject:  Re: A question for the Physics/Engineers
A higher psi stretches the tyre for more volume (thus displacement) so would probably aid boyancy, compared to a lower psi. Change in density would be negligible (compressed air is still a hellova lot lighter than, say, metal)
Author:  Ben_Sierra [ Fri Dec 10, 2010 12:31 pm ]
Post subject:  Re: A question for the Physics/Engineers
The change in size (i.e. displacement) of a tyre would be pretty small.

That said, the change in weight wouldn't be much either. It probably wouldn't make a whole lot of difference.

My scuba tank weighs around 2kg more full than empty. But thats nearly 4000psi, so 60 wouldn't make a lot of difference.
Author:  MacDaddy [ Fri Dec 10, 2010 1:40 pm ]
Post subject:  Re: A question for the Physics/Engineers
billrogers wrote:
Does a wheel... (rim, tyre and tube) At say 60psi pressure have better boyance than the same at say 10 psi.
Boyancy being flotation in water..
Regards Bill


GregDixon actually discussed this pressure difference in another thread, about tyres on road and sand... cant find it at the moment... but if i remember what he said, no it would not make it more buoyant, as the tyre will only inflate to a certain size... the more surface area you have, ( displacement of water ), will give the surface tension of the water, more area to push back on, and the more buoyancy it will have... but if you had really big tyres, like 35's or bigger, on a sierra, then it may have a good chance at being fairly buoyant :roll:

A bit of useless info... if you and your zook are ever caught underwater, you can breath from the air in the tyre, it will be stale, but it will keep you alive... for a while... :lol:
Author:  atari4x4 [ Fri Dec 10, 2010 1:56 pm ]
Post subject:  Re: A question for the Physics/Engineers
^^^ watch 007 much :wink:

i think this was the thread with the tech from greg?

http://auszookers.com/index.php?name=Fo ... hlight=psi
Author:  shabz [ Fri Dec 10, 2010 2:04 pm ]
Post subject:  Re: A question for the Physics/Engineers
why does a 5c coin sink - but a 500 ton ship float....

what macbear said - displacement. The amount of water an object 'displaces', must be heavier than the object, for it to float.

so a tyre with more air (higher psi) in it will make it heavier, ever so slightly - assuming the tyre size stays the same, the amount of 'displaced' water is the same - hence more air in the tyres will make it LESS boyant....but maybe not enough to sink it
Author:  shabz [ Fri Dec 10, 2010 2:06 pm ]
Post subject:  Re: A question for the Physics/Engineers
MacBear wrote:
A bit of useless info... if you and your zook are ever caught underwater, you can breath from the air in the tyre, it will be stale, but it will keep you alive... for a while... :lol:


I think it was from one of the Transporter movies......and i think mythbusters tried something similar
Author:  MacDaddy [ Fri Dec 10, 2010 5:18 pm ]
Post subject:  Re: A question for the Physics/Engineers
shabz wrote:
MacBear wrote:
A bit of useless info... if you and your zook are ever caught underwater, you can breath from the air in the tyre, it will be stale, but it will keep you alive... for a while... :lol:


I think it was from one of the Transporter movies......and i think mythbusters tried something similar


Bingo ! Yep i saw it on Mythbusters... it is difficult, but is doable... i have valve tools on all my valve caps, so if you just undo the valve a bit, and stick your mouth over the valve, its easy, but if you have to push the valve in by hand, it is much more difficult... :roll:
Author:  ajsr [ Fri Dec 10, 2010 8:19 pm ]
Post subject:  Re: A question for the Physics/Engineers
no the pressure will make no difference to the boyancy.
Author:  SuziBlu [ Sat Dec 11, 2010 2:40 am ]
Post subject:  Re: A question for the Physics/Engineers
Air can hold 1kg in water, that is, pure fresh water, nothing but H20, 1kg, in marine or salt water, it can hold, (average, the marine environment changes dramatically with location, summer, winter etc) 1.027kg

If you have a air container that is ay, 1 litre, then it will hold up, 1kg, if you add twice that volume of air, pressurize the container, it will hold an infinitesimally smaller weight. I can do the calcs, but my papers are home.

Displacement is the key here.

Concrete weights around sg2, so for the sake of the argument, it does, exactly.

So a cubic meter of concrete will weight, 2,000kg, it is a perfect cubic meter, so in water it displaces 1 cubic meter, so it weighs, 1,000kg.

Water is heavier than us, this is why we float, we displace more water than we weigh.

A drum displaces 250kg, it is exactly 1 cubic meter, it will float at 1/4 its volume, and support 750kg.

Hope that is understandable, im not a lecturer, but as a skipper, we do stability calculations a lot, we have to make sure we can float, not turn over and sink.
Author:  jake_ [ Sat Dec 11, 2010 8:13 pm ]
Post subject:  Re: A question for the Physics/Engineers
Its this

che_guitarra wrote:
A higher psi stretches the tyre for more volume (thus displacement) so would probably aid boyancy, compared to a lower psi. Change in density would be negligible (compressed air is still a hellova lot lighter than, say, metal)


vs this

sbbunno wrote:
would'nt it be heavier as (no matter how little) more air compressed into a small area making it denser?
maybe lol


A physicist would do a lot of calculations and tell you which one of these negligible changes is greater, an engineer will tell you that they're both negligible ;)
Author:  Ben_Sierra [ Sat Dec 11, 2010 9:14 pm ]
Post subject:  Re: A question for the Physics/Engineers
I'm an engineer. They're noth negligible. :P
Author:  Ammann [ Sun Dec 12, 2010 9:37 am ]
Post subject:  Re: A question for the Physics/Engineers
I'm a mathematician. And I would trust the engineer in these matters. :P

It is negligible for normal pressures. If you go up to a couple of thousand PSI the air would be liquid and have a similar density to water!
Author:  shep [ Sun Dec 12, 2010 9:43 am ]
Post subject:  Re: A question for the Physics/Engineers
no idea what you lot are talking about but i still want to contribute to the thread so here is a photo of a hole my dog made.
Image
Image
Author:  Highway-Star [ Sun Dec 12, 2010 9:46 am ]
Post subject:  Re: A question for the Physics/Engineers
Ducks also float in water So, logically... If...it...weighs the same as a duck......its made of wood. and therefore a witch!

If you a confusing witches with tyres, I recommend you seek help!
Author:  ajsr [ Sun Dec 12, 2010 9:46 am ]
Post subject:  Re: A question for the Physics/Engineers
:D :D :D good dog :lol: :lol:
Author:  lordfury007 [ Sun Dec 12, 2010 9:53 am ]
Post subject:  Re: A question for the Physics/Engineers
lol shep...
Author:  mighty_vites [ Sun Dec 12, 2010 10:25 am ]
Post subject:  Re: A question for the Physics/Engineers
simple answer take 2 wheel to your local pool one with 10psi one with as much as your game to put in it, chuck them both in and give $5 to some kid whos willing to drag them out if they sink.
Author:  gregdixon [ Sun Dec 12, 2010 10:43 am ]
Post subject:  Re: A question for the Physics/Engineers
A radial tyre at different pressure will float the same especially a 4x4 tyre, overall casing growth and added weight from the air is very insignificant.a bias tyre carcass will grow more but in smaller sizes I feel it would still not make a difference to boyancy. As everyone is saying it is more about displacement and weight if you want things to float.
We have however worked out some rough figures regarding 40.00R57 earthmover tyres. At 110 psi around 40kg of weight is added to the tyre from 0 psi. This tyre weighs around 3.5 tonne and 5 tonne with rim so 40kg is nothing.
Author:  Fatzook [ Sun Dec 12, 2010 10:46 am ]
Post subject:  Re: A question for the Physics/Engineers
gregdixon wrote:
This tyre weighs around 3.5 tonne and 5 tonne with rim so 40kg is nothing.


Surely that would float :lol:
Author:  gregdixon [ Sun Dec 12, 2010 10:53 am ]
Post subject:  Re: A question for the Physics/Engineers
I haven't seen it personaly but I believe it will.
Author:  atari4x4 [ Sun Dec 12, 2010 10:55 am ]
Post subject:  Re: A question for the Physics/Engineers
so i was right in a vague sort of way? :wink:
Author:  Ben_Sierra [ Sun Dec 12, 2010 12:10 pm ]
Post subject:  Re: A question for the Physics/Engineers
atari4x4 wrote:
so i was right in a vague sort of way? :wink:


More or less.... The displacement and weight changes will be so small in a tyre that it really won't make any difference...
Author:  Goldnomad [ Sun Dec 12, 2010 8:07 pm ]
Post subject:  Re: A question for the Physics/Engineers
Shep,

If the hole fills with water, will you dog float?

Robert
Author:  neofitou [ Sun Dec 12, 2010 10:50 pm ]
Post subject:  Re: A question for the Physics/Engineers
Author:  ajsr [ Sun Dec 12, 2010 11:40 pm ]
Post subject:  Re: A question for the Physics/Engineers
Author:  royce [ Sun Dec 12, 2010 11:44 pm ]
Post subject:  Re: A question for the Physics/Engineers
ajsr wrote:
wht then do dead bodies float??
not three days after death but straight away???


Only the fat ones :wink:
Author:  mighty_vites [ Mon Dec 13, 2010 5:36 am ]
Post subject:  Re: A question for the Physics/Engineers
if they die before they go in the water they still contain air, but if you drown them they will have lungs filled with water therefore sink.
it took me a few trys to get this one right.
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