Temperature. Thermometers. Measuring the temperature of a body
Temperature is a quantity showing how hot a body is; our senses are unreliable (after cold water, warm water feels hot), so a thermometer is used. A thermometer uses the thermal expansion of a substance (alcohol, mercury). Galileo made a thermoscope in the 1590s; the Frenchman Jean Rey made a water thermometer in 1631. In the scale of the Swedish scientist Anders Celsius (1701–1744), 0 °C is the temperature of melting ice and 100 °C that of boiling pure water at normal atmospheric pressure; the interval is divided into 100 parts. The lower limit is absolute zero, −273.15 °C; there is no upper limit. In nature −89.2 °C has been recorded in Antarctica (Vostok station, 1983). The range of a medical thermometer is 35–42 °C; a healthy person’s body temperature is about 36.6 °C. When measuring, hold the thermometer in the medium until its temperature equalizes, read the thermometer in water without taking it out, and look at the scale straight on. Note: mercury thermometers are now being phased out because mercury is poisonous; alcohol, electronic and infrared thermometers are more common today.
Observation: fill three glasses with cold, lukewarm and warmer (not hot, under 45 °C) water; hold one hand in cold and the other in warmer water for 20 seconds, then put both in the middle glass — see how senses mislead; then check with a thermometer. Safety: do not use boiling water; do not drop the thermometer, and if it breaks, do not touch the pieces — call an adult.