Sunday, September 27, 2009

Head bangers

Anyone who has ever taught knows about head bangers, you know the sort of thing that you thought was clear and obvious except there is one kid in the class . . . well, let's put it this way, after you figure it out you want to go bang your head against the wall mumbling "Never Again" endlessly. This is why teachers are always asking questions to check that they are getting through and why the good ones are always swapping stories about the truly eerie interpretations they get back from their class so they can avoid them next time.

Eli has one from last week. During a lab class he had to go to the little bunnies room for a short, but pleasant, interlude only to return and find the lab tech on the floor with the mercury cleanup kit and a bunch of panicked kids.

Eli: "WHAT HAPPENED
Kids: We dropped a thermometer and the mercury spilled all over the floor

Eli: We don't have mercury thermometers here
Kids: We dropped a thermometer and the mercury spilled all over the floor and we don't want to die (slight exaggeration)

Eli: We don't have mercury thermometers here

(Light dawns)

Eli: What color was the liquid in the thermometer
Kids: Blue

Eli: What color is mercury
Kids: We've never seen mercury

Eli goes and gets a mercury thermometer out of the stockroom

Eli: This is a mercury thermometer
Kids: Oh.

Moral: Most people under twenty these days have not seen a mercury thermometer or mercury or if they have have not registered that mercury is a silvery liquid (they may know that nearly all metals** are silvery, but not made the connection).

In his defense the lab tech thought Eli had handed out a mercury thermometer and was prepared to make Rabett stew after cleaning up

Change in lab SOP: Show the students a mercury thermometer in the first week. Explain that there are none in the undergraduate labs anymore.

It is literally impossible to figure out all of the “crooked” ways that people can think, but if you have heard about them, you can head some of them off at the pass.

The mem about the "lifetime of CO2" provides an opening for such a head banger which could be avoided by talking a bit of care. Say things like, an increased amount of atmospheric CO2 lasts centuries. Maybe add, CO2 exchanges quickly with the ocean and biosphere, but that is an exchange, not an increase or decrease.

** Copper and gold are exceptions

Via Atmos a whole blog full of head bangers, including this one

Got any stories?

13 comments:

William T said...

oh... so getting the kids to play with the mercury is out? Isn't part of the attraction of chemistry (and physics) that it's a great opportunity to do something 'dangerous'? Where's all the fun if you take that away. No wonder science is on the downward slide...

EliRabett said...

That's for the majors. . .

In any case the kids keep inventing new Darwin techniques.

Anonymous said...

My headbanger was after years of patiently explaining in physics classes that gravity acts down even in cases such as when a ball is thrown upwards. One year I gave a centripetal acceleration problem with a person at the equator. I included a diagram of a stick figure at the equator of a circular earth (head pointing to the right of the page). One students drew a free-body diagram and wrote a corresponding set of F=ma equations. Very nice except she had gravity acting down the page. I now always say gravity acts down toward the centre of the earth. I use the example as a warning to other physics teachers about being careful what you say.

Mike Coombes

Anonymous said...

About 40% of the general chemistry students at a moderately selective, Carnegie-1 State University believe that the bubbles in boiling water contain hydrogen and oxygen gases.

Robert P.

bigcitylib said...

When I was blowing up thermometers back in my highschool days they really were full of mercury. Don't know how much of that stuff I might have swallowed.

Do your kids show up drunk or on drugs? Don't tell them it makes class pass alot more quickly.

skanky said...

Our mercury fun was in a lab where we had a vacuum deposition plant with a mercury diffusion pump. One operator vented the chamber to see what the red powder inside the chamber was...

Martin said...

Eh, clouds are made of water vapour. Higher temperatures -> more evapotranspiration -> more clouds. Popular in some circles...

Anonymous said...

There was apparently a comment made at an examiners conference that a student had written that "silver chloride is a greenish gas". It was felt that this raised questions about the quality of chemistry practical work.

Anonymous said...

William T

I don't think kids can play with Mercury any more. But it is a very intriguing denizen of the Physical world particularly to younger students. It's obviously a metal but a liquid. It's startlingly dense in quantity and non wetting.
It is highly poisonous but many of us carry a mouthful of the stuff around with us for a large portion of our lives.
It has taken a long time to demystify these properties and I think it would be a shame if this progress was lost in a world of superstition.

I could go on......

mndean said...

In junior high, a classmate in our gym locker room was showing everyone a test tube half-full of mercury. He'd pour some out and fool around with it in the palm of his hand, then he'd drop in on the concrete floor where it seemed to...disappear! Of course anyone who was silly enough to look closely on the locker room floor could see tiny droplets of mercury everywhere. I suppose every kid who took a shower and walked through the area got a bit of it on the soles of his feet.

skanky said...

Did your school become great at athletics?

guthrie said...

No stories that I can recall, exccept a data point on mercury use in schools, ie that around 1990 in edinburgh our physics teacher swirled mercury around with his hands, saying he could touch it but we weren't, and that he wasn't mad yet. We were also allowed to pour mercury into a beaker and pour water on top as a demonstration of different densities. A very good demonstration. Mind you this was the sort of class they let us use transformers and if you connected them up wrong the plastic on the wires melted.

Holly Stick said...

I grew up in an old farm house with a small glass globe hanging on the wall near the coalstove in the kitchen. It was full of carbon tetrachloride. In the event of a fire the metal circle holding the globe was supposed to expand so the globe would fall and break and hopefully the carbon tet would douse the flames. Somebody in the family removed it when they learned that it was kind of poisonous and maybe a smoke detector would be better.