Physics: What makes sticky "sticky"?

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SunnyD

SunnyD

Belgian Waffler
Jan 2, 2001
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www.neftastic.com
Being the all knowing dad that I am, on the way to work this morning my son asked a simple question, something that normally a scientifically minded person like me should be able to answer rather quickly. But no.

The question was, "What makes sticky stuff stick?"

Simple question, right? Simple answer: Adhesion.

But that's not a good enough answer for a 10 year old who already knows more than a lot of high school grads (okay, that's not saying much these days - more than most smart high school grads). And it got me thinking too - I don't know what physical or nuclear properties are at work with adhesion. All I know is that superglue doesn't work the same was most glues do - as in it doesn't really use adhesion, rather it causes some materials to form new physical bonds. So then how does adhesion for normal "sticky" stuff work, in terms of physics and nuclear physics/chemistry?

Enlighten me oh great ATOT physicists!
 
IronWing

IronWing

No Lifer
Jul 20, 2001
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Van der Waals forces and in really tight situations, hydrogen bonding.
 
Born2bwire

Born2bwire

Diamond Member
Oct 28, 2005
9,840
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Van der Waals-London-Casimir forces.

EDIT: Quick synopsis:

The vacuum state for the quantum electromagnetic field has non-zero energy with fluctuating electric and magnetic fields whose observable mean are zero. The fluctuating electric fields of the vacuum induce polarizations in the molecules of the atoms of a given material. The polarization of the molecule/atom creates a temporary dipole moment. This dipole moment induces further polarizations in neighboring molecules. The orientation and proximity of the dipole moments between two polarized molecules affects the energy of the system. As such, the spatial orientation and position between these dipoles makes the energy profile, the potential, spatially dependent which causes a force (since force is the negative of the gradient of a potential). This is the London force as explained by Casimir. The other two Van der Waals forces assume that some or all of the molecules have permanent dipole moments as opposed to temporary dipole moments induced by the vacuum fields. Again, the spatial dependence of the potential of these dipole moments between molecules induces a force. In addition, because the orientation of the dipole moments also affects the energy of the system, then certain orientations are preferential at a given temperature. The resulting potential, when statisitically normalized against a Boltzman distribution for the temperature, also gives rise to an additional force.

EDIT EDIT: Quick quick synopsis:

Magic.
 
Last edited:
AMCRambler

AMCRambler

Diamond Member
Jan 23, 2001
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This reminds me of that episode of Futurama where they ask the what-if machine what's in the glue on envelopes.

Toad mucus!
 
dullard

dullard

Elite Member
May 21, 2001
26,061
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IronWing said:
Van der Waals forces and in really tight situations, hydrogen bonding.
Click to expand...
There is your answer.

And since the other post for Van der Waals forces is too technical for a 10 year old, let me over-simplify it for you. But it'll be good enough for a kid.

Molecules are filled with atoms with protons and electrons. These are positively and negatively charged. More importantly, the molecules and their protons/electrons are movable.

As we all know opposites attract and similar things repel. The north side of a magnet attracts the south side of another magnet and repels the north side of that other magnet.

If you put a positively (or negatively) charged item near another item, the positive charge on item #1 will repel the positive charges on item #2 and attract the negative charges on item #2. That is, the molecules and the electrons themselves in item #2 will rearrange. They will rearrange such that the positive parts are as far away from the positive item #1 and the negative parts are as close as possible to the positive item #1.

Suddenly you are left with a positive item #1 close to item #2 which has its negative parts on the surface. Since opposites attract, there is a force bringing them together. They stick.

The more surface area you have, the more chances there are for this rearrangement and the stickier things get. A gekko can climb walls since it has a massive surface area on its pads. So much area that these opposite attract rearrangment forces (called van der waals forces) make the Gekko sticky. But if the Gekko moves its legs away from the wall, the forces diminish (like a magnet only attracts things close to it) and the pads unstick.
 
Nik

Nik

Lifer
Jun 5, 2006
16,101
3
56
does it have anything to do with covalent electrons? god, it's been ages since I took a physics class
 
Jeff7

Jeff7

Lifer
Jan 4, 2001
41,596
20
81
AMCRambler said:
This reminds me of that episode of Futurama where they ask the what-if machine what's in the glue on envelopes.

Toad mucus!
Click to expand...
Wasn't the What-If Machine - it was when Fry got sucked into that Brain Sphere thingy, and he asked the question of the large brain, which then held all knowledge in the Universe.
(not quite) Everyone knows this.
 
ElFenix

ElFenix

Elite Member
Super Moderator
Mar 20, 2000
102,402
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blow his mind, the N marked end of a bar magnet is actually an S pole.
 
A

apac

Diamond Member
Apr 12, 2003
6,212
0
71
It's when the thread stays at the top of the list. Everyone knows this.
 
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