Today during Summer School activities, two questions were posed by instructors to students. Now we want to ask all of you readers of the blog, and invite you to comment and post your predictions – and we will let you know if you’re close. Don’t forget to explain why you made that prediction. (Even the scientists, who figured out the answers, had a hard time when I asked them how they would explain it to a non-scientist!)
1. Will ice melt faster in fresh water or salt water? Take a guess, and then you can try it at home – fill two glass with tap water at the same temperature. Put some salt in one glass and mix. Drop an ice cube in both glasses at the same time (if you like you can add food coloring to the water to compare). Were you correct? What do you think happened?
2. Will ice melt faster on metal or plastic? Here you can also take a guess, and then try it out. Put an ice cube on something metal and something plastic (and make sure it’s ok that the objects get wet). Were you correct? Why do you think that happened?
Hello Lindsay,
Here are my answers (do we get some of this nice caviar if we get the right answers?).
1. Ice will melt faster in fresh water. Adding salt to water lowers the temperature, hence ice will melt more slowly in salt water than in fresh water
2. Ice will melt faster on metal. Plastic is a better insulating material than metal, accordingly calories are better transferred to ice on metal versus plastic. There is a nice video on Youtube on the subject : http://www.youtube.com/watch?v=tREZMDqy1ds
Hope we’ll be challenged again in the next few days 😉
Pierre
Hi Pierre, thanks for submitting an answer! I would love to send you some caviar but I don’t think I have the technology to beam it to you from the Arctic. 🙂 About your answers, the second one is correct, good job! (Although I can’t see the YouTube video from here, but I’ll check it out when I get back to civilization.) For the first one, what’s actually happening mainly has to do with density. Salt water is more dense than fresh water, so the melted ice in the salt water glass will form a layer of cold fresh water on top of the salt water (like oil sits on top of water), so the ice won’t melt as easily. In the fresh water glass, the cold melted water is denser than the warmer water in the glass, and will sink, leaving the warm water at the top to more easily melt the ice. Make sense? I’ll try to post more activities, so keep following us and checking in!
Lindsay,
My daughter and I tried the experiment in our back yard this evening. Our results confirmed that the fresh water melted the ice cube faster that the salt water. Before we started, we both thought the salt water would melt the ice cube quicker, but our experiment indicated that we were wrong.
One thing we observed was that the salt water had a layer of fresh water at the top (a halocline?), while we didn’t see the same layer in the fresh water. We were thinking that maybe that meant there was a colder layer of water at the top, slowing the melting of the ice cube some.
You can see pictures of our experiment here:
http://flic.kr/s/aHsjHLs16z
Say hi to our friend Drew for us! Tell him he should introduce your mascot Willy to his mascot Flossie! (You could also ask him about the boiling temperature of salt water vs. fresh water as well.)
That’s awesome that you and your daughter tried the experiment at home. It sounds like you know what you’re talking about since you mentioned halocline, and also because you came to the right conclusion! It’s mainly all about density. Also, I asked Drew about Flossie, and at first he laughed and said “and who said that?” Now I’m learning a little too much about Flossie the inflatable sheep who has traveled the world! 🙂 I hope you and your daughter continue to follow us!