Sci/Tech: Hints for three curious things

 Which egg is which?

The difference you see is due to momentum: think about what a liquid can do inside an egg shell that a solid cannot do. If you try this, you may be able to relate this to why we feel giddy after spinning around—look up <semi-circular canals> to find out more.

Now here is a puzzle I don’t have an answer for: maybe you can find one: two cans of drink sit on the shelf in the refrigerator. You know that your mischievous friend has just shaken one of them, very hard. How can you tell which is which, before you open it?

(I would take the left-hand one, tell the friend I was choosing that one, point it at the friend, and go to open it—if the friend ducks, I would put that one down and take the other can, and repeat the experiment, but this time, I would open it, anyhow :-) This is well and good, but how can you tell if the friend isn’t there? I don’t know.

Strange matter

In science-speak, corn flour in water is thixotropic. Some clays and lahar, the earth that liquefies in a volcanic eruption, are also thixotropic. Lahars can be large, fast and deadly killers, so do not play with lahars.

The molecules in the starch are very large compared with molecules of water or other ordinary molecules. When you slap the surface quickly, they get tangled in each other, and this stops them splattering. In this way, the mixture behaves more like a solid.

If you move them slowly, or let them flow, the molecules can slip past each other, and so the starch behaves like a liquid. We call it a non-Newtonian fluid, and scientists speak of thixotropic and antithixotropic, so now you have the search words you need to learn more. You can also use custard powder (which is mainly corn starch) for this experiment, but watch out, because the custard leaves yellow stains if you spill it on anything.

The chemist who sits in my head says you should check to see if this yellow colour is an indicator for acids and alkalis. No, I don’t know the answer…

The most important phrases in science: “That’s odd…” and “I wonder if…”

Pile driver

The rice gets more and more packed down by repeated stabs from the knife until the rice is so compact that it presses against the blade of the knife with enough sideways force to overcome the pull of gravity on the jar.

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