Tuesday, July 5, 2011

Thermometers, yet again

If you stick your hand into a half full jar of sourdough pretzels in a Jersey July, you will feel your hand get noticeably cooler. Really. Try it.

If you measure the temperature inside the jar, it will be exactly the same as the temperature outside the jar. Any child with any sense and a respectable contempt for authority will tell you this. It's cooler in the jar!

It definitely feels cooler, yet the thermometer says otherwise. What's going on?

(Hint: this wouldn't work in Phoenix.)

Turns out experience is local. No national science curriculum can tolerate the very different results of my pretzel jar demo, a shame, really, because the children in Phoenix can very easily (and cheaply) discuss their results with the children in the humid halls of Bloomfield. Skype, blogs, wikis, heck, even phones.....

The humidity in the jar is much lower than the humidity in most of Jersey. Sodium chloride ("salt") is really good at grabbing water molecules from the air. The salt on the pretzels in the jar assures a low humidity environment, at least as long as you keep on the lid.

2nd graders do not need to know terms like "sodium chloride" or "hygroscopic." They should know, however, that science and intuition are not mates. They should know that science is based on what we call the "natural world" (itself a concept 2nd graders have a shot at grasping). They should know that science is testable.

I really don't give a rat's buttocks if a child can convert Celsius into Fahrenheit--that kind of skill matters, true, but that's not science, and it's something I can easily teach. I do care if a child is curious enough to wonder why her hand feels cool in a bucket of Snyder's Sourdough Specials.




Good Lord, I need curious children.We all do.

3 comments:

John T. Spencer said...

Joel tested grapes to see if they turn into raisins. Adults told him it wouldn't work. Probably shouldn't have worked, either. But in Phoenix, things evaporate fast. He dehydrated some of our tomatoes, too.

I don't think he could have duplicated these experiments in Jersey. Just a hunch. I'm not a scientist, but I do know this much: I'd love to test this hunch in Jersey and compare results.

ReadyOrNot said...

I have always noticed this! Thanks for the great explanation!

doyle said...

Dear John,

Joel is a natural scientist, and is fortunate to have folks who get that.

I will try the grape experiment in a few weeks when they're ripe--please remind me in early August if I forget.

I suspect you're right--the humidity will make it a much longer process here, and they may well rot before they get to the raisin stage.

Here's a question for your son--why don't raisins rot easily?


Dear ReadyOrNot,

Ah, I may have tipped my hand too much. In class, I would push this.

Why does a hand feel cooler when it's put into the lower jar? Yes, because of its lower humidity, but why does that make the air feel cooler?

Every child in Jersey knows "it's the humidity, not the heat," but very few understand the how.

Even fewer are curious enough to pursue the how--understandable given the way we 'teach' science.

Thanks for dropping by!