I recently soaked my sons onesie overnight in water and oxiclean. The legs and feet were sticking out of the bowl onto the counter. The next morning most of the water had traveled up and out though the legs (this bowl was not short either, it was part
Of our salad spinner.)
In: 142
My physics teacher said the siphon effect…which is what this is, is not fully understood.
It is a combination of capillary action, water cohesion, atmospheric pressure and gravity.
ELI5: Water likes to touch hydrophilic materials. Materials that are hydrophilic and have a lot of small pores/channels/capillaries (paper or clothes) are really good at sucking up water. This is the same mechanism (and material) for how plants and trees get water up and into their leaves.
Overexplained: to see how much water likes a solid material, we can put a drop of water on it. If it flattens out a lot, the surface is hydrophilic. If it beads up like on a Teflon non-stick pan, the surface is hydrophobic.
The quantification of this is the contact angle. A shallow, spreading contact angle <90 degrees is hydrophilic, and a steep, beading contact angle >90 degrees is hydrophobic.
The contact angle is best described as a competition for the surface at the molecular level: which prefers the surface more, water or air? In science, this is the 3-phase contact angle (material, water, air). You can also imagine repeating this measurement, but swapping the material for a different material, swapping the water for a different liquid like alcohol, or swapping the air to a different gas like argon (or swap the gas for a liquid like oil).
Source: am microfluidics engineer
the smaller the cross sectional area of the fluid flow, the stronger surface tension forces are compared to gravity. Stick pipes of varying diameters inside a large container of water. The water level will do up relative to the water in the container, and the smallest diameter pipe will have the highest water level.
Things generally tend to relax toward lower energy. In the water’s case, wetting the fabric via capillary action is a lower energy state than sitting in the bowl. Gravity is of course one of many forces acting on the water. If a force is larger than the gravity, the water has no problem going up. In a way, it’s “falling down” the energy potential of the fabric. It’s not as obvious as say, a magnet lifting a metallic object (of the right composition) or water moving up under pressure. It’s not one-way, so you might have also had water that had dripped down onto the counter.
The water in the wet fabric is also interacting with the atmosphere. In typical household conditions, the air is not at maximum humidity so water will also tend to evaporate. As water is removed from the fabric, more can be pulled from the bowl. One way of testing/demonstrating this would be having a bowl of water as the control, and different shapes of paper and fabric acting as wicks, propped up and hanging over the edge.
Candle wicks and oil lamps actually use this, though instead of just evaporating, the wax/oil goes into a gas phase and burns.
Water can’t defy gravity, but it can be made to move upwards against gravity through capillary action. Capillary action is the tendency of water to move up into a narrow space, such as the fibers of a cloth or the small spaces between the threads of fabric. This happens because the adhesive force between water molecules and the surface of the material is stronger than the cohesive force between the water molecules.
In the case of your son’s onesie, the adhesive force between the water molecules and the fibers of the fabric was stronger than the cohesive force between the water molecules. This caused the water to be drawn up into the fabric, even though the legs and feet of the onesie were sticking out of the bowl.
The taller the narrow space, the stronger the capillary action. So, the longer legs of the onesie provided a greater surface area for the water to be drawn up into.
As a result of capillary action, the water was able to travel upwards against gravity and soak into the onesie. The next morning, most of the water had traveled up and out through the legs of the onesie.
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