# Homework Help: Surface energy theoretical questions work shown need help!

1. Oct 30, 2009

### johnq2k7

1.) When woven material is dry, air will pass directly through. When immersed in water however, clothing can be used to trap air and provide buoyancy.

a.) With the aid of the diagram, explain why this is so?

need help explaining theoreticallly?

b.) Give an eq. which can be used to calc. the buoyance force (Fb) which can be provided by a vertical cylinder of radius r_c, made from a cloth with a uniform pore size of radius r_p. assume that the cloth is completely wetted with water which has a surface energy y and that the cylinder can be as long as is necessary

need help coming up with an equation here

c.) based on your equation what would be the best type of material and shape for a cloth float?

2.) When a drop of water is placed between two microscope slides they stick together.

a.) with the aid of a diagram showing the shape of the interfaces, explain the force holding them together.

my work: they stick together because the force can be balanced horizontally and vertially, since the pressurs accross the lower and upper slides are the same ignoring gravitational effects therefore they stick together... not sure if my explaination is correct?

b.) Will the sheets still stick together if they are immersed in water? Explain

no because of the pressure differences between the surface and water would cause the two slides to separate.. not sure if my explaination is correct..

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution