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Make a simple thermometer

You will need:

  • 1 screw top container
  • 1 clear straw
  • Something to make a hole with eg. nail or hand drill
  • Food colouring
  • Hot water bath, ice bath and hair dryer (optional)
  • Moulding clay and a permanent marker (in the video below we use a balloon with a hole through it instead)

simple thermometer


  1. Carefully bore a hole into the middle of the lid of the container. Make sure that the hole made is only slightly bigger than the diameter of your straw.

    SAFETY: If children are to do this, please ensure that hand drills that are not electrically powered are used. Alternatively, hand drill the lids prior to children commencing the experiment or use balloon material or another easily pierced material.

    ALTERNATE VERSION: Use a bottle with a small opening (eg soft drink bottle)

  2. Thread the straw through the hole and seal the join with the moulding clay (Important: Roll the moulding clay around the edge of the lid, making sure of a good airtight seal. 

    As per the video above, you can also use a balloon with a hole in it to make a tight seal around the straw and bottle opening.
  3. Fill your container to the brim with water and add a couple of drops of food colouring.

    Adding food colouring to the thermometer
    Adding food colouring to the water bottle thermeter
  4. Gently blow into the straw - blowing hard may cause the water to rush up into your face!

    Blowing into the thermometer
    Blowing into the bottle to force coloured water into the straw.
  5. Blowing into the straw forces air into an enclosed space, thereby increasing the pressure within the container. If your seals are airtight, you will find that water will rise up the straw once you stop blowing. This may require some trouble shooting!
  6. Mark the level of the water with a pen - this mark identifies where the water will be when at room temperature.

    Marking thermometer with a pen
    Marking thermometer with a pen 
  7. Now hold the container between your hands, thereby gently heating the water inside. Alternatively you can use a hot water bath or even a hairdryer.

    SAFETY: Using electrical appliances near water can be dangerous, please have an adult demonstrate this experiment
  8. If all has gone well you will find that the water will have traveled up the straw.

    Water level rise in thermometer
    Water level rise in thermometer 
  9. Now try placing the home made thermometer into an ice bath, what will happen to the water?

Why Does This Happen?

When liquids are heated they expand. Knowing that water expands when heated helps scientists to model the movement of ocean currents around the world.

Click here for a link to CSIRO remote sensing images of water temperatures around Australia

This same principle is used in the every day mercury thermometer. Mercury is used within thermometers as it is liquid at -39oC and expands rapidly when heated, as well as that it's convex meniscus allows for accurate temperature readings.

Reference: Brady, J. E. & Holum, J. R. (1993). Chemistry. The Study of Matter and Its Changes.
John Wiley & Sons, New York

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