Читать книгу Exploring Kitchen Science - The Exploratorium - Страница 25

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Drumroll, please: The egg that

resumed its spin after being stopped

is the raw egg! Inside its shell, the liquid

is still spinning, and this motion makes

the entire egg go around again. Meanwhile,

the reason the hard-boiled egg stands up is

actually rather complicated. Mathematicians Keith

Moffat and Yutaka Shimomura calculated that

the egg translates some of its spin energy into

gravitational energy, lifting the egg up until its

center of gravity is over the point of contact

with the table.

What’s the Deal?

Have a friend place the two eggs on the kitchen table

and mix them up while you look the other way. (Hey, no

peeking!) Then give both eggs a good spin.

Once you get them twirling and whirling, stop

both eggs with your hands and then let them go. One will

mysteriously spring back into a spin; can you determine

which egg it is? Think about it, carefully considering what

a liquid interior and a solid interior could do to the egg’s

motions. Then write down your choice on a piece of paper.

Now put this egg aside and turn your attention to

the other one. Get it turning very, very fast. Once it’s going

swiftly enough (at least ten revolutions per second), it might

do something crazy: Without any help from you, this egg will

suddenly and spontaneously rise up on end and spin like a

top. Again, give it a good think—is the cooked egg the stand-

up-and-go spinner, or is it the raw egg?

Try This Next!

Grab your raw egg and some table

salt. Make a small pile of salt on

a flat surface, and then place the

egg on the pile with its longer axis

pointed up. Gently rock the egg back

and forth until it feels stable in its

upright position and then . . . let

go. Your egg should remain stand-

ing! Carefully blow the extra salt

away from the egg’s base as it stays

perched upright on a point below

its center of gravity: the point inside

the egg where it balances left and

right, top and bottom, and backward

and forward. The egg stands on end

because the salt enlarges the base

below the center of gravity. The cubic

grains act as a support structure.