AboutDan Fink Expertise Though my experience is mostly in the fields of electricity, magnetism, and physics, I have a broad science background. My career is in the field of alternative power sources -- solar, wind, water and battery power. But any questions about electricity, magnetism, energy conservation, power generation, electric motors, and even general physics are very welcome--especially from kids. They ask the best questions of all! I pride myself in answering science questions accurately, with ideas for SAFE, easy experiments that kids can perform by themselves--and that let them prove the answers to their own satisfaction. I think science should be fun, and available to everyone, regardless of age.
Experience I have volunteered in our local public schools for 5 years. I currently make presentations at our schools about electricity and magnetism, with a focus on solar, wind, water and other alternative power sources. I try to demonstrate at our schools how easy it is to make electricity, with simple devices using spinning magnets and coils of wire--powered by wind, water, bicycles, gerbils...etc. And of course solar panels! I am the webmaster of Otherpower.com, an alternative energy website. I have lived 10 miles from the nearest power pole for 11 years--I make all my own electricity from scratch with sun, wind and water.
Publications Otherpower.com
Wondermagnet.com
Co author of the book "Homebrew Wind Power" ISBN 978-0-9819201-0-8
My articles appear regularly in such magazines as Home Power and Back Home Education/Credentials BA Technical Journalism
Question I am in 6th grade.
I recently did an experiment with hot and cold water and cotton balls. The cotton ball always sank to the bottom of the very hot tap water glass in about 3 seconds. The cotton ball in the very cold tap water would take anywhere from 30 sec. to 1 minute or more. -- I did the experiment 10 times and my results were consistent.
Is it water tension differences or molecular differences in the water at different temperatures that make this "sinking time" so different? -- Or is it something else. Please help me understand.
Thanks for your help.
This is my Mom's email address.-- her name is Lynn
Answer Hi Gracie
You are thinking along exactly the right lines here, you did indeed figure it out! Your experimental results are consistant with the theory behind them.
Water molecules are held together by 'cohesion' forces - water is very polar, and the molecules are strongly attracted to each other. When you add heat energy to water, the molecules are more easily able to overcome their mutual attractions. This results in both lower density and viscosity, and lower surface tension.
The water is drawn into the hollow cotton fiber tubes by capillary action--this happens when the water molecules' attraction to the sides of the little cotton fiber tubes begins to grow compared to the attraction of the water molecules to themselves. Water's attraction to a solid is called 'adhesion'. The hotter the water, the less cohesion to keep it together, and therefore the more adhesion can act to draw it up into the tubes in the cotton fibers. It's less dense and less viscous, so the water in the middle of the cotton fiber tubes can move faster into the tubes to soak the cotton, while the water on the sides of the tubes is still sticking.
You can also do this experiment (and be able to measure the exact distance and speed with which capillary action works) with tiny little glass tubes held endwise onto the surface of the water....adhesion and capillary action will draw water up into the tube until gravity counteracts it.
