Capillary action at different temperatures

[SCalver]

Hi guys,

I'm doing a project at the moment revolving around capillary action and surface tension. Today I conducted an experiment to observe capillary action in a capillary tube and paper towel at different temperatures of water. I don't understand why I've got the following results:

As you can see, they are complete opposites of each other. This seems to make sense according to my calculations with Washburns and Jurins equations. But I can't figure out the physics behind this. The capillary tube radius is 0.2mm. The paper towel was 1.5x23cm with 5cm submerged in water for a time of 120 seconds.

I also did an experiment investigating the relation between surface tension and soapy water. I tried different concentrations of soap solution and added them dropwise onto the top of a circular metal disk very carefully until failure occured. Any ideas why my graph seems to level out after while?:

here is a picture of what I mean by failure (excuse my crappy camera)
non failure:

Failure:

any help appreciated

 

[Asim Riaz]

. Thank you!First of all, for the first experiment, the reason why the results of the capillary tube and paper towel were opposite is because of the way surface tension works. Surface tension is an attractive force that acts between the molecules of a liquid. It is stronger in liquids with higher surface tension and weaker in liquids with lower surface tension. The higher temperature of the water in the capillary tube caused the water to have a higher surface tension, so it was able to move up the tube more easily than the lower temperature water in the paper towel.For the second experiment, the reason why the graph levels out is because the soap solution is reducing the surface tension of the water. As the concentration of the soap solution increases, the surface tension decreases until it gets to a point where it can no longer hold the weight of the disk on the surface of the water. This is why the graph levels out - the surface tension is not strong enough to hold the weight of the disk any more.