Mathematics K–6 · Years 3–4
Reading a thermometer: partial units on a scale
Measurement and space
The idea
A scaled instrument has marks that stand for fixed steps, and a reading between two marks is estimated from how far along the gap the level sits.
Safety card
Hazards
- warm water
- glass thermometers can break
Controls
- warm water is drawn from a tap and checked to be at or below 45 degrees before children use it; spirit thermometers only (no mercury); an adult handles breakages
Note
Warm tap water at or below 45 degrees Celsius only; no heating equipment is used, so the Chemical Safety in Schools package does not apply.
What you need
- 3 spirit-filled (alcohol) thermometers marked in 1 degree Celsius steps, range at least minus 10 to 50 degrees
- three plastic cups: one of crushed ice with a little water, one of room-temperature tap water, one of warm tap water no hotter than 45 degrees Celsius; a spoon for stirring and paper towel
- a recording table with columns cup, prediction, reading, reading to the nearest half degree
How to do it
- Read the classroom air temperature on a thermometer left on the desk for two minutes. Look at the scale: count the marks between two labelled numbers and say what each mark stands for.
- Predict the temperature of each cup, then stir the iced water with the spoon, place a thermometer in each cup and wait one minute before reading. Read to the nearest mark, then estimate to the nearest half degree.
- Take the thermometer out of the iced water, dry the bulb with paper towel and watch the level rise. Read it every 30 seconds for three minutes and record the readings.
- Compare readings between pairs for the same cup and discuss why they differ by up to a degree.
- Read the outdoor temperature from a thermometer in the shade and compare it with the classroom reading.
What you should see
The stirred cup of crushed ice and water reads 0 degrees Celsius within about 1 degree while ice remains in it, the room-temperature cup reads close to the air reading, and the warm cup reads no more than 45 degrees, the limit it was checked against. Each mark on the scale is 1 degree and a level midway between marks is read as a half degree. After removal from iced water and drying, the reading rises quickly at first and then by smaller and smaller steps as it approaches the air temperature, so the readings in the table climb by less each time.
What changes
- What you change
- the cup the thermometer sits in
- What you measure
- the temperature reading in degrees Celsius
- What you keep the same
- one minute in the cup before reading
- the bulb fully under water
- reading at eye level
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- A reading between two marks must be rounded to the top mark.
- The thermometer shows the right temperature the instant it goes in the water.
Curriculum references
The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.
- Mathematics K-10 Syllabus (2022), NSW Education Standards AuthorityMAO-WM-01
- Australian Curriculum v9AC9M4M01
Sources
The pages the author read to write this activity.