I just did this little demonstration for my five-year-old: I took a 12ml syringe with no needle attached, and filled it about 15% with hot tap water, turned it tip up, and used the plunger to push out the air. I then plugged the tip of the syringe with my finger, and pulled the plunger back, creating a partial vacuum (obviously, some air leaks back in). The water immediately started to boil, thereby demonstrating that the boiling point of water goes down as air pressure goes down.
Another step one can add (I didn't) is to touch the water that had just been boiling and observe that it's not boiling hot (I guess if one does that with a five-year-old, one accompanies it with warnings that normally water that had just been boiling is hot). A more sophisticated experiment would involve measuring the temperature of the water before and after the boiling, comparing with a control sample in another syringe that hadn't been made to boil, and seeing if the boiling removes thermal energy (as I expect it does).
4 comments:
I have a 3 year old and will have to keep the water and syringe in mind when he gets a little older.
That is a great experiment. I'm going to try it with my kindergarteners tonight.
I wonder if using alcohol instead of H2O would let one do this with room temperature liquid.
Prof. Pruss,
I was reading some book reviews from a science magazine and came across a book that you might find interesting. It's a book filled with activities and projects that are designed for dads and their kids. The books go by Geek Dad. For example, one book is titled Geek Dad: Awesomely Geeky Projects and Activities for Dads and Kids to Share, and another one titled The Geek Dad Book for Aspiring Mad Scientists: The Coolest Experiments and Projects for Science Fairs and Family Fun.
The author Ken Denmead provides information about the design and complexity of the projects along with their cost and time, as well.
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