MadSci Network: Chemistry
Query:

Subject: How and why does water temperature affect cohesion and adhesion?

Date: Mon Feb 14 13:08:35 2000
Posted by darlene davis
Grade level: 7-9 School: (for son at Franklin Middle School)
City: Reisterstown State/Province: Maryland Country: U.S.A.
Area of science: Chemistry
ID: 950555315.Ch
Message:

My son recently completed a science experiment, as follows:  He placed one 
plate face-down on a baking sheet on the floor.  He placed a second plate 
face-up on top of the first (so that the plates were back-to-back).  He 
then attached a suction cup and a string to the top plate. At the other 
end of the string was a paper cup.  The string was hung over the top of a 
lever (creating sort of a "scale" with the paper cup on side and the plate 
on the other).  He tested to see how many pennies were needed to lift the 
top plate, first when the plates were dry, and then when the bottoms of 
the plates were wet with water of varying temperatures. As expected, it 
took more pennies to separate the wet plates than the dry plates, but we 
wer surprised to find that it took the most pennies (around 300) to 
separate the plates when wet with the hottest water we tested (140 
degrees), and it took the fewest pennies (around 120) to separate the 
plates when wet with the coldest water we tested (37 degrees).  Can you 
explain why?  Thank you. 


Re: How and why does water temperature affect cohesion and adhesion?

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