# Why do we pour hot tea from higher to lower distance to cool?

## If the tea is poured in a plate the tea will be cooled fast. But if it is in glass then it will cool slowly. From this we can understand that the surface area of the tea is less in the glass and the surface area is more in the plate. So the heat transfer easily takes place where there is more surface area. So to increase the surface area we make the hot tea poured from higher distance to lower distance and the tea cools fast.

If the tea is poured in a plate the tea will be cooled fast. But if it is in glass then it will cool slowly. From this we can understand that the surface area of the tea is less in the glass and the surface area is more in the plate. So the heat transfer easily takes place where there is more surface area. So to increase the surface area we make the hot tea to be poured from higher distance to lower distance and the tea cools fast.

Explanation:

We know that heat always flow from hot body to cold body.

When tea is hot and the air surrounding it is cold the heat from tea is transferred to the air surrounding the tea.

When the heat transferred directly to air the process is fast and the tea cooled quickly. But when the heat is transferred through glass wall (as its heat transfer coefficient is low) the heat transfer process is slow and the tea cooled very slowly.

If we increase the surface area to make tea to contact air directly to transfer heat the cooling will be fast. So we pour the tea in the plate or pour it certain times by lifting the glass upper to another glass which is in the lower position.

How it cools?

There are two types of heat transfer take place. Let us learn a little thermodynamics concept to understand this.

1. Heat directly transfers from the hot tea to the cool air as the air is in lower temperature than the hot tea.
2. Little amount of the tea gets evaporated to air (The liquid tea evaporated and  becomes air - This is called phase change process -  Changing from one state to another state – solid to liquid, liquid to gas, solid to gas or vice versa). For a phase change to occur the energy is required. This little amount of tea which gets evaporated takes this energy (heat energy) from surrounding tea and makes the surrounding tea cool.

Through these two types of heat transfer the tea is cooled very fast rather than allowing it to cool in the glass itself.