How a thermometer works
Is a pool full of ice water warm enough for swimming? Not for you! But
for a penguin, it might be just right. You and the penguin have
different ideas about how \”warm” the water is.
You can easily find out how much heat is in
the water. You can measure the temperature of the water with a
thermometer (thuhr [mahm]{.smallcaps} uh tuhr).
A thermometer is a closed tube. At one end it has a bulb filled with
liquid. When you put the bulb in something—the swimming pool, for
instance—the liquid inside the thermometer gets warmer or cooler until
it reaches the same temperature as whatever is around it.
If the liquid in the thermometer gets warmer, the molecules speed up and
push away from each other. The liquid expands (ehk
[spandz)]{.smallcaps}—it takes up more space. It pushes out of the
bulb and climbs higher in the tube.
If the liquid in the thermometer gets colder, the molecules slow down
and move toward each other. The liquid contracts (kuhn
[trakts)]{.smallcaps}— it takes up less space. It slides down the tube
toward the bulb.
The numbers and marks on the thermometer are called degrees (dih
[greez).]{.smallcaps} They show the amount of heat. When the liquid
expands or contracts, the number it reaches is the temperature you are
measuring.
So you and the penguin don’t have to agree that the water is \”cold” or
\”hot.” You can read the thermometer. It will tell you in numbers
exactly how hot—or how cold—the water in the pool is.
