If you touch a substance with your bare hand, you may feel cold or hot. The measure of this property of matter, hotness or coldness, is called temperature. We can agree in that the higher the temperature, the hotter the object, and vice versa. However, “hotness” or “coldness” are subjective sensations and do not define temperature properly. For example, the temperature of the same weather may be hot for one person and cold for another person.

You have learnt above that heating increase both the temperature of the substance and the average kinetic energy of its particles proportionally. Later, it is known that the temperature of a substance depends on the average kinetic energy of its particles. Temperature is defined as a measure of the average kinetic energy of the particles within the substance.

All particles in a substance cannot have the same speeds at the same temperature. That is why, we say temperature depends on average speed or average kinetic energy. If the average kinetic energy of all particles in a substance is high, then the substance is at a higher temperature. The average kinetic energy of water at 10 °C is smaller than the average kinetic energy of water at 40 °C, as shown in Figure 2.