Physics/maths Question

R B Customs · 23 Oct 2006 at 18:15

damn this is an interesting thread

a few people are missing the point a little i think. i am aware that there is a lot missing from my original question. but i suppose you could look at this not from a nuclear way but from a more diagramatic approach.

i thoguth of this question years ago in school and it just came back to me recently. it troubled bme beacuse a circle is an arc, no finish and no end.

push a glass, or a mug up to a wall and look at the rim, follow it round... the moment the edge of the rim curves round toward the wall the wall is the exact moment that it starts to curve away.

i suppose this theory would work with egg shaped objects based on how its curvature is constant.

im startign to believe the answer is Zero.

sendos · 23 Oct 2006 at 18:20

IF the sphere and the surface are completly perfect and have no iregularites then the surface area would be 1 planck meter or 1.61624 × 10-35m which is the smallest possibly unit of size according to planck's constant.

SteveOBHave · 23 Oct 2006 at 19:03

sendos said:
IF the sphere and the surface are completly perfect and have no iregularites then the surface area would be 1 planck meter or 1.61624 × 10-35m which is the smallest possibly unit of size according to planck's constant.

Isn't that still assuming that the two objects have an atomic (and therefore a subatomic) makeup? Plancks Constant is based around quantization (according to Wikipedia -http://en.wikipedia.org/wiki/Planck%27s_constant) so by virtue of the question we are unable still to quantify an area.

I agree R B Customs, the answer has to be either Zero or Infinity depending on which relation you choose to apply. The irritating thing is that in a practical and physical sense we 'know' that something is touching the other surface because we can push on it.

Rather than the question being a physics question I suspect it is almost open to philisophical discussion

Jotun · 23 Oct 2006 at 19:09

The answer is none of the ball, as the two objects never touch because as the two objects are brought closer to each other, the repulsive forces between the atoms increases greatly so they cannot touch!

Psyk · 23 Oct 2006 at 19:09

SteveOBHave said:
IIRC it includes all objects. i.e. all matter and light exhibits both wave and particle properties although only at an atomic scale with 'solid' matter.

Can't remember the formula, but there is a way to find your own wavelength depending on your mass and what speed you're moving. Although your wavelength will be very tiny

Lagz · 23 Oct 2006 at 20:00

It all depends on how you define 'touching'.

Technically nothing ever 'touches' anything else. When I put my hand against a wall it isn't technically touching it on a physical level (i.e: the atoms in my hand are not physically touching those in the wall). What actually happens is when my hand and the wall come extremely close together a huge force is generated to stop my hand moving through the wall.

Hence the answer is 0 in both cases, but it all depends on how 'touching' is defined.

Grrrrr · 23 Oct 2006 at 20:03

Lagz said:
Technically nothing ever 'touches' anything else. When I put my hand against a wall it isn't technically touching it on a physical level (i.e: the atoms in my hand are not physically touching those in the wall). What actually happens is when my hand and the wall come extremely close together a huge force is generated which greatly reduces the probability of my hand moving through the wall.

Since we're being picky

Lagz · 23 Oct 2006 at 20:07

Grrrrr said:
Since we're being picky

Well the probability is essentially 0 anyways, pfft

.

SteveOBHave · 23 Oct 2006 at 20:28

LOL this was always going to be reduced to semantics - has been quite mentally stimulating tho

sendos · 23 Oct 2006 at 22:07

SteveOBHave said:
Isn't that still assuming that the two objects have an atomic (and therefore a subatomic) makeup? Plancks Constant is based around quantization (according to Wikipedia -http://en.wikipedia.org/wiki/Planck%27s_constant) so by virtue of the question we are unable still to quantify an area.

Surely the two objects would have to have an atomic makeup... although hyperthetically they could be completly solid object i.e no gaps between atoms and electrons etc just pure mass. I wonder what the amount of mavity a 10cm in diameter peice of purely dense mass would kick out. probaly equivelent to a moon.

AJUK · 23 Oct 2006 at 22:20

That would weigh an awful lot more than a moon. A black hole is nothing more than an extremely dense (almost no gaps between atoms) object. So a 10cm diameter totally solid object would create a black hole, or at the very least you couldn't lift it.

Jokester · 23 Oct 2006 at 22:28

Evil-Penguin said:
The answer is none of the ball, as the two objects never touch because as the two objects are brought closer to each other, the repulsive forces between the atoms increases greatly so they cannot touch!

Quoted for truth.

Jokester

yer_averagejoe · 23 Oct 2006 at 22:30

Infinetly small. But when you get down to it, they're not actually touching.

PhilthyPhil · 23 Oct 2006 at 22:44

AJUK said:
That would weigh an awful lot more than a moon. A black hole is nothing more than an extremely dense (almost no gaps between atoms) object. So a 10cm diameter totally solid object would create a black hole, or at the very least you couldn't lift it.

Nuclear density is of order 10^18 kg/m3, the mass of the moon is of order 10^22 kg so it would be several orders of magnitude more massive. A black hole is not defined by density, it is defined by the inability of anything to escape its region of space, which is bounded by its Schwarzschild radius. The density of a black hole is inversely proportional to its mass, for example a supermassive black hole would have a density less than water.

SteveOBHave · 23 Oct 2006 at 22:54

sendos said:
Surely the two objects would have to have an atomic makeup... although hypothetically they could be completely solid object i.e no gaps between atoms and electrons etc just pure mass. I wonder what the amount of mavity a 10cm in diameter piece of purely dense mass would kick out. probably equivalent to a moon.

OP question was:

Hypothetically speaking: ( ideal situation)

if you had a perfectly FLAT, SMOOTH surface

and an absolutely PERFECT sphere / ball of about 10 CM in diameter

you rest the ball onto the perfect surface. how much of the ball is touching the surface?

So by rights we shouldn't make assumptions about the variables in the equation.

Interesting question that tho, something that is absolutely dense...

yer_averagejoe · 23 Oct 2006 at 22:57

an object the size of a tennis ball (6.5cm diameter) with a density to be just great enough to be considered a black hole would weigh:

21,920,000,000,000,000,000,000,000kg

twenty one thousand nine hundred and twenty sextillion kg.

= 4 and 2/3 the weight of the earth.

sendos · 23 Oct 2006 at 22:58

SteveOBHave said:
OP question was:

So by rights we shouldn't make assumptions about the variables in the equation.

Interesting question that tho, something that is absolutely dense...

Ah right now i get why more first comment about the planck meter couldnt be applied to the question

SteveOBHave · 23 Oct 2006 at 23:03

PhilthyPhil said:
Nuclear density is of order 10^18 kg/m3, the mass of the moon is of order 10^22 kg so it would be several orders of magnitude more massive. A black hole is not defined by density, it is defined by the inability of anything to escape its region of space, which is bounded by its Schwarzschild radius. The density of a black hole is inversely proportional to its mass, for example a supermassive black hole would have a density less than water.

Ugh - astrophysics - my head hurts LOL

Such a dense mass probably wouldn't matter (excuse the pun) since everything near it would be sucked/crushed into it's mavity well... Kinda brings us back to the original answer

= 0

Vonhelmet · 23 Oct 2006 at 23:10

As has been said, they never really touch, but if you want to know how many atoms are in immediate proximity to each other... it depends on the atomic structure of the sphere, as it will vary depending on how the atoms are arranged. Some people have said it could be three, but if the atoms are arranged differently it could be 5 or 6 or who knows what.

SteveOBHave · 24 Oct 2006 at 08:37

vonhelmet said:
As has been said, they never really touch, but if you want to know how many atoms are in immediate proximity to each other... it depends on the atomic structure of the sphere, as it will vary depending on how the atoms are arranged. Some people have said it could be three, but if the atoms are arranged differently it could be 5 or 6 or who knows what.

We could define a point on the sphere where the contact takes place using:

Wikipedia said:
The points on the sphere with radius r can be parametrized via

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$fa6565b9c256107089fcd63e760e3b38.png$

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But like you say we'd have to define the properties of the two surfaces (spheres surface and plane surface) to attempt to get a 'probability' of a number of atoms being in proximity.