Science Buddies: "Ask an Expert"

I dropped a lid upside down in my cup (it had a few drops of juice in it). It stuck.
I then compared it with a glass with a few drops of water, and it stuck, too. We can explain the water, but are wondering why the one with juice stuck longer. What happens to juice when it dries? At a grade 2 science level? Thanks. We can't seem to find the answer. Does the sugar become a solid again after the water evaporates? Do the crystals attach between the surfaces? Thanks.

This is a popular question and one that's asked often on the internet. A Google search turned up dozens of really good explanations.
http://kidshealth.org/kid/closet/experi ... ticky.html
http://www.basf.ca/group/corporate/ca/e ... rter/sugar (an interesting podcast)
http://www.madsci.org/posts/archives/19 ... .Ch.r.html

Is there more to your question? Take a look at these site, try "why is sugar sticky" in your favorite search engine and write back if you don't see an answer you like.

Howard

Hi, thanks for getting back to me. Yes, we did come across this information. What is confusing though, is why does the kid stick longer with juice than with the water? The same things seem to be happening, so what part is making the difference that makes the lid stick to the juice longer than the water?

The juice has sugar in it. When the juice dries, the water evaporate away and leaves the sugars and other parts that makes juice taste like juice. Sugar is hydrophilic and will readily absorb moisture from the air. So it's going to be slightly damp and sticky after it dries.

If sugar is sticky because of the bonds in the molecules and juice has sugar (which water doesn't), then I'd say the answer to your question is the sugar content in the juice. If you want to ry an experiment, add sugar to water and see if sugar water is as sticky (and behaves the same way) as juice does.

Ok, that I didn't know. Fascinating. Thanks!! I will try that experiment for sure.