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like spaghetti thrown at a wall. is it a function of suction or more like inertia? or is this a question i should be asking in the chemistry section?

2007-07-20 10:40:12 · 4 answers · asked by Anonymous in Science & Mathematics Physics

4 answers

There are really three parts to this question. Why doesn't it rebound, why doesn't it immediately fall, and why does it cling to the wall as it falls like, well, spaghetti?

Why doesn't it rebound? Countless tests run in spotless labs have all converged on the conclusion that wet spaghetti has a very low coefficient of restitution, ranging from zero to 0.00000000034 with a confidence level of 0.99.

Why doesn't it fall? For this you can thank Lepage's Effect, which gives flour-based aqueous gels like boiled semolina spaghetti a distinct adhesivizing and viscosifying influence. (I.e., it's sticky.) Similar mixtures have been used from the Middle Ages on by schoolchildren and monks to adhere paper flowers and sparkling dust to their manuscripts.

Why does it cling on the way down? Let's not forget good old surface tension, which is the basis not only of dry adhesion but of wet cling as well. To the extent that it contains liquid, the mess you threw at the wall will tend to remain in contact, wetting the surface as it descends and retaining some of the embedded solids if they are small enough. Separating the stuff from the wall takes energy as it requires stretching the free (i.e., non-contacting) wet surface which fights surface tension. Thus we see a natural and persevering affinity between saturated pasta and vertical surfaces.

2007-07-20 12:03:47 · answer #1 · answered by kirchwey 7 · 0 0

Well, I think this can be answered fairly logically. Okay, wet object, check. Dry object, check. You lob the wet object at the dry, it sticks for a little while then slides off. What's happening is that the wet object sticks to the wall because the moisture in the wet object does not allow the wet object to rebound off the wall. What happens is that the moisture in the object acts to discharge the object's energy as it impacts the wall. Also, the moisture of the object probably makes the object sticky. For instance, in your example of spaghetti, the moisture causes the noodles to release some of its starch content which, in a semi- liquid form, makes it sticky. Objects, like wet towels, can also stick, the moisture content of the object will dictate how likely it is to stick to a wall or any other dry surface. High concentrations of liquid may make the object stick to the wall as the object's material creates a very loose vacuum between the wet and dry object. Or it could bounce off.
Oh, and by the way, according to Quantum Physics, there is a remote chance that the object will pass through the wall without resistance. Just thought I'd share that.

2007-07-20 10:50:39 · answer #2 · answered by White Rabbit 2 · 0 0

take a towel which weighs the same as does a piece of duck (canvas). Throw them when wet at the same wall. The towel has a better chance of remaining up there longer.
The interplay of the water and the fibers of the towel create a great number of pockets or voids where the water is stored, wicked into place there. When the wall surface is connected - especially with a bit of force, these pockets each acquire the opportunity to behave like a suction cup of very low pressure. As a group, they hold the towel.
Conversely, the duck is too stiff to permit numerous pockets to connect, so it falls off.
The best description of this phenomenom is a new product. This adhesive tape uses nanotubes, stacked beside each other, making a surface of the set of nanotubes' ends. As any lateral motion occurs, the sides of the nanotubes slide against each other as the side force bends the tubes. When the ends become canted, each forms a nano-sized void between the moving surface below and the tube end. Together, these billions of nanotubes generate a vacuum which is a very good example of how geckos' feet stick to things.

2007-07-20 12:30:09 · answer #3 · answered by science_joe_2000 4 · 0 0

I believe it's a matter of surface tension.

Once the wet object has slapped onto the wall, both are wet, but there are just two wet exposed water surfaces: the outside of the object, and the inside of the object (which is in contact with the wall).

If the object falls off the wall, there will be three surfaces: the outside of the object, the inside of the object, and the wall itself: all water surfaces.

Because of surface tension, the creation of that third water/air surface requires energy. If the object is heavy enough, gravity provides the energy: the work done by gravity in peeling the object off the wall will make up for the creation of the surface-tension energy.

2007-07-21 08:38:00 · answer #4 · answered by ? 6 · 0 0

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