Laboratory work. Measuring air and liquid temperature with a thermometer
You need: a laboratory thermometer (alcohol or electronic), warm and cold water, a measuring cylinder, plastic cups instead of glass, a stirring stick and a clock. First find the value of one scale division: divide the difference of two neighbouring numbers by the number of divisions between them (for example, 10 divisions between 10 °C and 20 °C means one division is 1 °C). Hang the thermometer on a wall away from sunlight and heaters, and after 5–6 minutes, when the reading stops changing, write down the room temperature. Then pour 100 ml of warm water (about 40–50 °C, prepared by an adult) into a cup, put in the thermometer and after 1 minute read t₁ without removing it. Likewise measure t₂ of 100 ml of cold water. Then mix the two and measure t₃. Usually t₃ lies between the two temperatures, and for equal amounts is close to the average (t₁ + t₂) : 2; the small difference is due to heat lost to the surroundings and the vessel.
Laboratory work (in groups): measure room, warm water, cold water and mixture temperatures and record them: “t₁, t₂, t₃, (t₁ + t₂) : 2”. Safety: use only warm water prepared by an adult (not above 45 °C); no boiling water, gas or hot plates; keep a glass thermometer away from the table edge and do not touch the pieces if it breaks.