Hot and cold
We sense hot and cold with sensitive spots in the skin called thermoreceptors, which send signals to the brain. In physics “cold” is not a separate thing: if a body’s temperature is lower than ours we call it cold. Heating means giving heat to a body; cooling means taking heat away. When a cold spoon is put into hot tea, heat passes from the tea to the spoon. Ice in juice takes heat from the juice and melts itself. A refrigerator carries heat from inside to outside, so its back is warm. Temperature is measured on the Celsius (°C) or Fahrenheit (°F) scale. We use Celsius: water freezes at 0 °C and boils at 100 °C. On the Fahrenheit scale water freezes at 32 °F and boils at 212 °F; it is used mainly in the USA.
Three glasses: hot (poured by an adult), warm and cold water. Put one hand in cold water and the other in warm water for a minute, then put both hands in the warm water: what do you feel? How reliable is judging temperature by touch?