Heat Transfer in Nature

There are three ways in which heat is transferred from one place to another - conduction, convection, and radiation.

Conduction of Heat

The process of heat transfer from the hotter part of an object to the colder part is called conduction. In this process, the particle that gets heated, passes the heat on to its neighbour, and so on. However, the particles themselves do not move from their positions.

Materials like metals that allow heat to pass through them easily are called good conductors of heat. Because metals are good conductors of heat, we use utensils made of metals for cooking. In solids, heat transfer takes place mainly through the process of conduction.

Materials such as glass and wood do not allow heat to pass through them easily and are poor conductors (insulators) of heat. Clay and porcelain are also poor conductors of heat - that is why tea or coffee kept in such cups stays hot longer.

Woollen fabric traps air in its pores and as air is a poor conductor of heat, it reduces heat flow from our bodies to our surroundings. As a result, we feel warm. Similarly, air trapped between the layers of clothing acts as a poor conductor of heat and keeps us warm. The presence of air between two thin blankets is the reason why we prefer them over one thick blanket to keep us warm.

There are houses with outer walls that are constructed using hollow bricks that keep them warm in winters and cool in summers. This happens because the air that gets trapped in the hollow bricks is a poor conductor of heat.

Convection

The process of heat transfer through the actual movement of particles is known as convection.

Water, like air, gets heated up by the process of convection. Here, heat transfer takes place by the actual movement of particles of liquids and gases from one place to another.

Land and Sea Breeze

People living in coastal areas experience an interesting phenomenon caused by the heating and cooling of land and water at different rates. As the land gets heated faster than water during the day, it causes warm air above the land to rise. This causes cooler air to move from the sea towards the land. This movement of cooler air from the sea to the land is called sea breeze. Hence, in hot places, sea breeze relieves people from the heat. That is why, windows of the houses in coastal areas are placed facing the sea.

At night, the process reverses. In the absence of sunlight, land cools down faster than the water in the sea. As a result, the air above the sea is warmer and rises up. Cooler air from the land then moves towards the sea, creating a land breeze. Thus, people living near the seashore experience that the direction of the wind reverses in the day and night.

Radiation

The heat transfer takes place directly from the hot object. This process known as radiation. The heat of the Sun reaches us through this process. Heat transfer by radiation does not require any medium.

All objects radiate heat. A hot utensil kept away from the flame cools down after some time. The hot utensil cools down by radiating heat to its surroundings.

Light-coloured clothes reflect most of the heat that falls on them, and therefore, we feel more comfortable wearing them during summers. Dark surfaces, on the other hand, absorb more heat, and therefore, we feel more comfortable with dark-coloured clothes during winters.

Water Cycle

Water exists in three states in nature. As a liquid, it fills the oceans, rivers, and lakes on the Earth. As a solid, it forms snow, ice sheets, and glaciers in the mountains and the polar regions. As a gas, it exists in the form of water vapour in the Earth’s atmosphere.

During summers, some of the snow and ice gets converted to water due to the Sun’s radiation and flows down as rivers, and ultimately into the oceans. The melted ice is replenished by fresh snow during winters.

Water in the oceans, rivers, and lakes gets heated due to the Sun, and as a result, it evaporates as water vapour. Water also evaporates from trees and plants through transpiration.

When water vapour rises up, it cools down and condenses to form clouds. Clouds bring rain, snow, and hail. This process is called precipitation.

The continuous movement of water - upward as water vapour and downward through precipitation, passing through soil, rocks, and plants, and finally returning to water bodies, is called water cycle. Thus, the water cycle helps in redistributing and replenishing water in rivers, lakes, and oceans. It also serves to conserve the total amount of water on the Earth. Rainwater that falls on the surface of the Earth, flows into ponds, lakes, rivers, and oceans or seeps into the ground.

Seepage of water beneath the Earth

The process of surface water seeping through soil and rocks is called infiltration. Water can infiltrate more readily if the spaces between soil and rock particles are wider, open, and interconnected.

The water that seeps through gets stored in the pore spaces of sediments and the openings in rocks beneath the surface as groundwater. The underground layers of sediments and rocks that store water in pore spaces are called aquifers. This is the water we extract by digging wells or
drilling bore wells into aquifers. This water may be a few metres to hundreds of metres below the ground, depending on the location.

However, groundwater is not unlimited. The growing water requirements of an increasing population have led to excessive groundwater extraction. Additionally, decreased vegetation cover and increased concrete surfaces in urban areas have limited water infiltration. As a result, groundwater is getting depleted. To address this, rainwater harvesting and recharge pits are used to replenish groundwater. Hence, the water cycle ensures that groundwater sources are recharged, thereby helping to ensure a sustainable groundwater supply.