My Science School

Energy resources are of two types. Those resources that are formed over millions of years and cannot be replenished are known as non-renewable energy resources, such as coal, natural gas, and crude oil. Those resources that can be replenished are known as alternative energy resources, such as, hydropower and wind power, biogas, and solar energy. Although nuclear energy too is inexhaustible, it is not considered an alternative energy resource because of the risks associated with it.

Without liquid water there would be no life on the Earth. No other planet has liquid water, and hence no life is possible on any planet other than the Earth. Water is found everywhere - in milk, vegetables, fruit, meat, air, and ground. Water is the habitat for a large number of plants and animals. Fish, algae, crustaceans, and many more organisms live in the oceans. Frogs jump in puddles and ponds, and sea birds move on the surface of water. Water carries ships, from small boats to giant container ships, which are used for transportation.

Ice floats in water because the solid form of water is lighter; it means the ice is less dense than the liquid form. This is unusual because in other substances it is just the other way round. Initially, water behaves like other substances. When it is heated, it expands and evaporates. When it is cooled, its volume becomes smaller. After a certain temperature, however, water becomes ‘wayward’. At 4°C, it reaches its densest state. On further cooling, it expands again! Thus, water behaves abnormally. This is also known as anomaly of water. On freezing, i.e., at 0°C, its volume increases again. This is the reason why water bottles full of water burst if they are kept in deep freezer for a long time. 

 The word ‘wet’ means moistening. If we dip our hand in water and take it out, it gets covered with a film of water. It is moistened, and the wet film can be removed easily with a towel. The reason for this is that water molecules come in close contact with the skin surface and stick to it. This is known as ‘adhesion’. Water, however, cannot stick to oily skin and drips off because oil and water do not ‘like each other’. In this case, we do not feel the wetness because water does not moisten the skin so well. 

On a warm skin water evaporates; i.e., it is converted from liquid to gaseous state. In this process, the skin loses some of its heat; as a result, the surface of the skin is cooled. This process is known as ‘evaporative cooling’. Our body also uses this effect to regulate the body temperature when it is hot. It secretes sweat, which evaporates, and thus cools down the skin. We can also cool the cold drinks in this way while camping by wrapping the bottle in a wet cloth and placing it in wind.

Water striders are very light-weight insects. Their legs are covered with millions of tiny hairs that trap air bubbles. These air bubbles along with surface tension of the water keep water striders afloat. Water molecules attract one another very strongly; this is known as ‘cohesion’. The resultant force acts downwards on the surface of water, above which there is only air and no water, so a flimsy solid layer is formed. This effect is known as surface tension. Because of surface tension water always ‘tries’ to keep the smallest possible surface area. Thus, raindrops on the window pane are spherical. 

Container ships do not sink because of buoyancy. Ships made of steel are constructed in a very special way so that they do not sink. The weight of water displaced by the hull of the ship must be greater than the weight of the ship (along with the load it is carrying). As a result, the water below the ship pushes it upwards with a force known as buoyancy. We also experience buoyancy when we swim and feel lighter in water than on land. Floating tires increase the buoyancy further. In contrast, submarines must overcome the buoyancy in order to sink. For this, special tanks are flooded with water. 

Water has huge power. We can feel this on our bodies when we cross a sea or river. The power we get from water is called hydropower. Hydropower has been one of the first forces used by human beings to simplify their work. For example, tasks such as turning wheat into flour, processing wood to make paper, making textile, and turning hard metals into various interesting shapes, which were difficult to do earlier, have been made easy by using hydropower. Dams are made by erecting huge walls in water to generate electricity. Even today there are ferries and boats without engines that use the force of flowing water. Even tides in the oceans can be used to produce energy. 

A watermill uses a large wooden or metal wheel to generate power. It consists of many small blades, over which the flowing water of a stream runs; this wheel is called the ‘water wheel’. The flowing water rotates the wheel. This rotational movement produces electricity when connected to a generator. Although mills were used to generate hydropower in earlier times in all countries, people in the underdeveloped countries use them even today. Electricity produced in such a manner is pollution free and does not harm our environment. 

Dam walls are mostly made of a material called concrete. These dams retain a large amount of water. The retained water puts very high pressure on the lowermost layers of water. If the water in these lowermost layers is diverted, it flows at a very high speed, and hence a high energy is produced with the help of a device called turbine. In the turbine, the energy is used to generate electricity.  Continue reading "How is electricity generated by using a dam? "

High and low tides come alternately, that is, one after the other. In high tides, the level of water rises and covers a part of the coast, and in low tides it flows away again. This energy of the tides is used to run turbines. Special water turbines are used in tidal power plants. Water - rising in case of high tides and receding in case of low tides - can flow through these turbines in both the directions. Electricity is generated in tidal power plants due to the rotary movement of the turbines. These power plants need a tidal hub - the difference in the height of water between high and low tides - of more than 5 m to be able to work economically. Such a power plant is in the French Bretagne, in St. Malo. Here, the tidal hub is at 12-15 m. 

Ferries without engines are driven by the flow of water. They are attached to a wire cable, which is spanned across the river by means of two short ropes. When the ferryman shortens one of the two short ropes with the help of a device called ‘winch’, the ferry is tilted at an angle to the current, and the force of the current propels the ferry across the river.

 

At room temperature, there is always some air dissolved in water. The colder the water, the more air is dissolved. Air becomes less soluble in water as the temperature rises. When the water boils the air is released in the form of bubbles. Two thousand years ago, an attempt was made to use the power of steam with Heron’s ball, but the great breakthrough came only with the steam engines. The steam engine improved by James Watt is the most well-known. A little later the steam engines were used to drive locomotives and paddle steamers - the modern steam turbines followed later. 

 

The Heron’s ball is a bellied vessel, which is partly filled with water and sealed with a cork. A pipe which is open on both the sides goes inside the vessel through a hole in the cork. When the air pressure inside the vessel becomes higher than the atmospheric pressure, the water pushes out through the pipe. The internal air pressure can be increased in different ways: by connecting two vessels, by blowing air in the vessel through another pipe, or by heating the water. The water vapour that is formed needs more space and pushes water out from the pipe; the water actually sprays out. In principle, the Heron’s ball is the first steam engine. 

James Watt is often called the inventor of the steam engine, but in reality he improved upon the working steam engine of Thomas Newcomen and got his design patented in 1769. In the steam engine of James Watt, hot steam is passed inside the cylinder not just from the side but alternatively from top and bottom. The expansion force of the steam causes a piston in the cylinder to rise and fall. Watt converted this up and down movement into the rotational movement of a flywheel. From there, the force generated by steam could be transferred to machines - to sewing machines or weaving looms.