A thermometer is a tool that tells us how hot or cold something is. We can use a thermometer to check the air outside, a room, water, or a person’s body. Learning to read a thermometer helps us choose what to wear and understand the weather.
The red line shows the temperature.
Understanding Reading a Thermometer
A thermometer works because some materials change in a regular way when their temperature changes. In a liquid thermometer, the colored liquid spreads out as it gets warmer. It takes up more space and moves upward in the thin tube.
When it cools, it shrinks and moves downward. Digital thermometers use an electronic part that changes its electrical behavior with temperature.
Both kinds need a marked scale so their changes can be turned into a number. Scientists make these scales by comparing thermometers with carefully controlled temperatures.
Reading the small marks correctly is an important skill. First, find the numbered marks on either side of the liquid level. Next, count the equal spaces between those numbers.
If ten spaces lie between twenty and thirty, each small space represents one degree. Read at eye level. Looking from above or below can make the liquid seem to stop at the wrong mark.
Take your time when the level sits between two lines. A careful estimate is better than a random guess.
Temperature is connected to the movement of tiny particles. In warmer matter, particles move or vibrate more quickly on average. In cooler matter, their movement is slower on average.
This helps explain everyday changes. Ice melts when it gains enough thermal energy. Water can become steam when it gains much more.
A metal spoon left in hot soup becomes warm because energy moves from the soup into the spoon. The energy keeps moving from warmer objects to cooler objects until they become close to the same temperature.
Students meet temperature in weather reports, cooking, health checks, science labs, refrigerators, and heating systems. The same temperature can be written on two common scales. Water freezes at zero degrees Celsius and thirty two degrees Fahrenheit.
Water boils at one hundred degrees Celsius and two hundred twelve degrees Fahrenheit at sea level. It is useful to notice which scale is being used before comparing numbers. Safety matters too.
Never use a damaged glass thermometer. Do not touch hot containers just to judge their temperature. In an experiment, give the thermometer time to reach the temperature of the material, keep its sensing end in the material, and avoid letting it touch the bottom of a hot container.
Key Facts
- A thermometer measures temperature.
- Temperature tells how hot or cold something is.
- °F means degrees Fahrenheit.
- °C means degrees Celsius.
- Look at the top of the red line to read the temperature.
- A higher red line means warmer, and a lower red line means cooler.
Vocabulary
- Thermometer
- A thermometer is a tool that measures how hot or cold something is.
- Temperature
- Temperature is a number that tells how hot or cold something is.
- Degrees
- Degrees are the units used to measure temperature.
- Fahrenheit
- Fahrenheit is a temperature scale often used for weather in the United States.
- Reading line
- The reading line points to the number that matches the top of the red liquid.
Common Mistakes to Avoid
- Reading the bottom of the red liquid, not the top. The temperature is shown by the top of the red line.
- Skipping numbers between marks. Count by the pattern on the thermometer, such as 10, 20, 30, or by 2s or 5s.
- Thinking higher numbers mean colder. Higher numbers mean warmer, and lower numbers mean cooler.
- Forgetting the unit, like °F or °C. The number needs its unit so we know which temperature scale is being used.
Practice Questions
- 1 A thermometer has the red line at 70°F. What temperature does it show?
- 2 The red line moves from 60°F to 80°F. How many degrees warmer is it now?
- 3 Two thermometers show 40°F and 75°F. Which one shows a warmer day, and how do you know?