How do suction cups work?

[sorgoth]

I recently stuck a decoration on my window with the little plastic suction cups on the back, and it suddenly hit me that I have no idea WHY it sticks. Anyone here know?

[richardm]

I'll have a stab at it. When you squeeze the cup against the window, you squeeze out the air from under it. Then the elastic plastic or rubber that the cup is made out of tries to return to its original shape. This causes an area of lower pressure under the cup, and the higher external atmospheric pressure pins it to the window.

Perhaps :D

[Psi Baba]

Originally posted by sorgoth
I recently stuck a decoration on my window with the little plastic suction cups on the back, and it suddenly hit me that I have no idea WHY it sticks. Anyone here know?
That will be the least of your problems. When it falls off in two days, you'll be grumbling, "Why don't these %&#@ things ever stick?"

[Bikewer]

A bit of moisture (or vaseline) around the edge helps longevity, makes a better seal. Yep, air exerts around 14 psi at sea level (nitpickers- do NOT post the actual figure!) so a good suction cup can hold a fair weight.

The powerful mechanically-asisted cups used by window-glass workers can hold quite a bit, and humans can cllimb sheer objectst with them.

[patnray]

Every see that demo where a vacuum cleaner picks up a bowling ball? Minimum weight for a bowling ball is 8 pounds. If the vacuum creates only 1 pound per sq. inch of pressure difference, then you only need 8 sq. inches of contact area to pick up the ball. Notice how big of a funnel they place between the vacuum and the ball...

Of course it is air flow velocity, not vaccuum pressure, that determines how well a vacuum cleaner works, so the demo tells you nothing about how well a vacuum cleaner actually cleans...

[Paul C. Anagnostopoulos]

And all these years I thought that pressing the suction cup against the wall drew the suckons to the surface, causing the cup to be sucked against the wall. Another bit of high school science down the drain.

~~ Paul

[arcticpenguin]

Originally posted by Bikewer
A bit of moisture (or vaseline) around the edge helps longevity, makes a better seal. Yep, air exerts around 14 psi at sea level (nitpickers- do NOT post the actual figure!) so a good suction cup can hold a fair weight.

If you REALLY want longevity of your sucking application, try a drop of super glue for that moisture.

[ceptimus]

Originally posted by sorgoth
I recently stuck a decoration on my window with the little plastic suction cups on the back, and it suddenly hit me...That'll teach ya. Use Blu Tac in future.


...now how Blu Tac works is really hard to explain...

[Bikewer]

Actually, the super glue might not work as well. (though the partial vacuum would help) I tried super-gluing a broken blown-glass figurine once. Seemed to work fine; the seam closed almost invisibly, and all was well.
About an hour later, when the glue dried, there was a little "tink" sound and the poor little unicorn's head fell off....

I guess the adhesion with glass was good when wet, but on drying there was none!

[sorgoth]

Ah. So it DID have somethign to do with air pressure. (I had been pondering it.)


How DOES blu tac work? Yknow, the blue gum like substance?

[exarch]

As far as adhesive powers go, I still like the gekko's feet the best. And they can bond to almost any surface they want (not just smooth shiny surfaces like the suction cup).
Apparently they make a molecular bond that is strong enough for the gekko to carry the weight of a human when attached to the ceiling. They haven't actually done that experiment ofcourse, since the poor little gekko itself cannot take that much weight.

[JSFolk]

Originally posted by Paul C. Anagnostopoulos
And all these years I thought that pressing the suction cup against the wall drew the suckons to the surface, causing the cup to be sucked against the wall. Another bit of high school science down the drain.

~~ Paul

Funny, I thought it was posting any bit of evidence for evolution that draws the suckons to the surface.

[Bikewer]

Suckons....I read about those in physics....No, wait....those were gluons.

[exarch]

And don't forget klingons ... :D

[Bikewer]

All right, this skit is getting too silly now.....

"Captain, there's Klingons on the starboard bow!"

"Well, scrape them off!"

[sickstan]

Does this mean that she couldn't really suck a golf ball through a garden hose??

[Bikewer]

Or the chrome off a trailer hitch....