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

I do not know how the adhesion and cohesion properties of water are affected by temperature. But I think that there just might be an alternate explanation for your observations.

I presume that the plates used were not paper plates. If they were paper plates then the following explanation may not be valid.

I suspect that when the plates are put togehter (back to back) that there is some empty space between them due to some degree of a rim on the bottom of each plate. I suspect that when warmer water is used the gas trapped (when the plates are put together) is initially warmed by the warm water. This trapped sample of warm gas is initialy at atmospheric pressure.

As this trapped sample of warm gas cools during the course of the addition of the pennies, the pressure of the trapped gas drops, and it is fairly well sealed against leakage of air in from the outside by the presence of the water at the places where the plates are in contact. With this lower pressure of the trapped gas on the inside, the atmospheric pressure (higher pressure) on the outside tends to hold the plates together until a larger force must be applied to pull them apart. As the water used is warmer, the gas is heated more and the pressure drop is greater when it cools.

I hope that this provides an answer to your question. If I can be of more help, don't hesitate to contact me.

Dr. Jerry Franzen
Chemistry Department
Thomas More College
333 Thomas More Pkwy.
Crestview Hills, KY 41017