How Do Thermometers Work?

What You'll Learn

• Temperature tells us how hot or cold something is
• A thermometer has a liquid inside that expands when hot and shrinks when cold
• As the liquid expands, it climbs up a tube with numbers
• The number at the top of the liquid tells you the temperature
• Digital thermometers use sensors instead of liquid

Words to Know

Thermometer

A tool that measures temperature

"The thermometer said it's 72 degrees."

Temperature

How hot or cold something is

"The temperature is high today."

Expand

To get bigger and take up more space

"The liquid expanded when warm."

Contract

To get smaller and take up less space

"The liquid contracted when cold."

Check What You Learned

Fun Facts

• A thermometer measures temperature — how hot or cold something is

  Source: Britannica

• Liquid-in-glass thermometers contain alcohol or mercury that expands when heated and contracts when cooled

  Source: National Institute of Standards and Technology

• As the liquid expands, it rises in a calibrated tube with numbered markings

  Source: NIST

• The height of the liquid column corresponds to a specific temperature reading

  Source: Britannica

• Digital thermometers use thermistor sensors that change electrical resistance with temperature

  Source: NIST

• Galileo Galilei created an early thermoscope around 1593, considered a precursor to the thermometer

  Source: Britannica