What are thermometers?

A thermometer is a tool that tells us how hot or cold something is by showing its temperature.

Imagine you have a cup of soup on the table. You want to know if it's warm enough to eat, but you can't see the heat, you just feel it. A thermometer works like a special friend who can tell you exactly how warm or cool the soup is without touching it. It uses little bits inside that move when they get warmer or cooler, and this movement shows numbers on its screen.

Some thermometers have a liquid inside them, like red liquid in a glass tube. When the liquid gets warmer, it expands (gets bigger) and moves up the tube, showing higher numbers. When it gets colder, it shrinks and goes down, showing lower numbers.

Other thermometers are digital, like the ones you find in your bedroom or on your phone, they use tiny sensors that can count how much heat is around them and show the number on a screen instead of a liquid moving up and down.