Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
Answer, and give a reason.
Capillary rise: , where is the angle of contact. A liquid that wets the tube () rises; one that does not () is pushed down.
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) The tiny gaps between the fibres act as capillary tubes, and water, which wets cotton, climbs into them.
Step 2. (b) The upward pull goes as the edge length, , but the weight held up goes as , so .
Step 3. (c) Hoeing breaks up the fine channels near the surface, so water cannot climb up them and evaporate.
Answer: Capillary action in each case.
Watch out. A narrow tube lifts higher, but it holds less water.
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