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Build a Barometer

In this activity, students use their knowledge about air pressure to build a barometer, an instrument that measures atmospheric pressure, which ia also known as barometric pressure.

Air pressure is affected by temperature and density (i.e. how many air particles in a particular space).

The Sun heats the Earth unevenly. When air is heated by the Sun, the air particles move faster and expand. This reduces its density relative to the cooler air around it, causing it to float upwards and leaving a low-pressure gap below it. Surrounding higher-pressure air will want to rush in and fill in the low pressure gap, which we feel as wind.

Wind is the flow of air from a high pressure zone to a low pressure zone. Air always flows from a high pressure zone to a low pressure zone. To help students remember the direction of air flow, they can use the phrase “Winds blow from high to low".

A barometer works by sealing a chamber of air with a material that can expand or contract. The flexible material caves in or bulges outward depending on whether the higher pressure is inside or outside the chamber.

If the air outside has a higher pressure, it will push into the lower pressure zone inside the barometer; it pushes down on the flexible material. If the air pressure outside is lower, the trapped air inside the barometer pushes up into the lower pressure air; it pushes the flexible material up.

A needle, attached to the flexible material, will deflect upwards if the pressure outside is higher. The needle will deflect downward if the pressure inside is higher.

In a low-pressure region, warm air expands, rises, cools, and loses its ability to hold its water vapour. This forms clouds (condensation), often leading to rain. In a high-pressure region, cool air contracts, sinks, warms, and gains the ability to carry water vapour (evaporation). This leads to clear and sunny skies.

By tracking the movement of a barometer, we can predict the weather that will be entering our area in the next week.

While tracking the movement of the homemade barometer you could also have students take photos or bring in newspaper clippings of local weather maps.


  • Explain how air pressure works.

  • Discuss how air pressure affects our daily lives.


  • Per Pair of Students:
    a jar
    a balloon
    strong elastic band
    uncooked spaghetti noodle
    sheet of paper

Key Questions

  • Part 1:
    • What have I sealed inside the jar?
    • At this time, is the air pressure inside the jar the same as outside the jar?
    • How will the balloon membrane react if the air pressure outside the jar rises?
    • How could we use this information (and this jar), to keep track of the rising and falling of atmospheric pressure?
  • Part 2:
    • If the pressure outside the jar is higher, what happens to the balloon? What happens to the needle?
    • If the air pressure outside the jar is lower, what happens to the balloon? What happens to the needle?
    • What do we need to keep track of the needle going up or down (we can’t memorize the exact location of the needle every day without a reference point)?
    • It’s important not to leave the jar near a source of heat or cold…why?
  • Part 3:
    • Does a pattern emerge between the position of the needle and the weather outside?
    • Does your barometer predict the weather that has already taken place, the weather taking place today, or the weather that will take place in the future?

What To Do

Demonstrate the following before student pairs make their own.

Part 1

  1. Cut the stem off the balloon.
  2. Stretch the balloon over the opening of the jar.
  3. Secure the balloon to the jar with the elastic.
  4. Ask students the key questions below.

Part 2

  1. Tape one end of the spaghetti noodle to the center of the balloon to act as a needle.
  2. Ask students the key questions below.
  3. Fold the sheet of paper in thirds to form a triangular column. Tape the open side so that it doesn’t lose its shape.
  4. Stand the column next to (but not touching) the end of your spaghetti noodle. Make a mark on your column where the column is pointing today. Draw a symbol that represents the current weather outside (raining, cloudy, partly sunny, sunny).
  5. Repeat step 4 every time you come to class for at least 3 weeks.

Part 3

  1. Keep track of your results in a table that contains the following information:
  • date
  • direction of needle
  • indicates high or low pressure
  • actual barometric pressure (on the weather network)
  • my weather predictions
  • actual weather conditions


  • Why does the atmospheric pressure decrease when we go up in an airplane?
  • Is the pressure on our bodies more or less in water than in air? (Hint: air rests on top of water)
  • Draw a model of the eardrum and describe why some people’s ears hurt when in an airplane taking off or landing.
  • Why do mountain climbers need to take their time when climbing tall mountains such as the Himalayas?