The finer the water is sprayed on a fire, the faster it evaporates. As a result, it takes away energy from the flames and cools down the burning substance to such an extent that it can no longer catch fire again. Water extinguishes fire by creating a film of water over the burning substance, and thus cutting off its oxygen supply. Water has many advantages such as it is non-toxic in nature and is available in plenty. Water can be used to extinguish fire as discussed above, but this is not true in all cases of fire, for example, oil burning in a pan can be extinguished better by covering it with a lid rather than using water, burning metals would split the water chemically through the heat, and oxygen will be released which will intensify the fire further. Similarly, water cannot be used in cases where the fire has originated due to an electric fault.
Unlike a petrol engine, an air - fuel mixture is not used in a diesel engine, but instead pure air is sucked in a cylinder. The air is compressed so strongly in the cylinder that it gets heated up to 700-900°C. The diesel fuel is then sprayed finely in this hot air and immediately gets ignited because of the high temperature. The expansion of combustion gases pushes a piston downwards. This force is transferred to the wheels of the car via shafts. The gases released in the combustion are discharged via the exhaust.
The Latin word fossilis means ‘unearthed’ or ‘excavated’ because we need to excavate these fuels. In other words, they are buried deep inside the Earth and we need to dig them out. Fossil fuels are made of plants and animals that died millions of years ago and were converted - by the processes inside the Earth - into coal, crude oil, or natural gas. The energy stored in these fossils can be released and used by burning them. Searching for coal or crude oil, pumping out these fuels from the depths, and transporting them require a lot of effort and time. The crude oil must then be converted into petrol for cars.
By using acoustic or sound signals, the geologists identify the places where oil can occur on the Earth. They study these regions by looking in the rocky layers and taking samples at different depths. If the studies point to a deposit of oil, a hole is drilled in the ground in the hope of finding oil. Scientists believe that crude oil arose from the smallest sea organisms, the planktons. After dying, the planktons sank to the seabed and were covered with sand and sludge over a long period of time. Because of the high pressure exerted by this layer, the dead mass got converted into digested sludge, which gradually got converted into crude oil. Since oil is lighter than rock, it rose up and was held in pores of the rock, like water in a sponge.
At places where crude oil is found, huge, hollow chisels drill several hundred metres deep in the Earth to reach the rocky layers containing oil. In some cases, the oil shoots out because of the pressure of the natural gas, which is found frequently with crude oil. Pumps are used to bring the oil to the surface if the pressure is not adequate. The oil is then transported to the big harbours with ships or through pipelines—hundreds of kilometres long. Sometimes it is also transported directly to a refinery, where it is processed further.
Natural gas is a combustible gas or a gas that burns easily, which is formed in the same way as crude oil. Since natural gas is lighter than crude oil, it is often found above the deposits of crude oil, in the form of a cap. Methane is the main component of natural gas which is made up of different gases. Natural gas itself is colourless, odourless, and lighter than air and it burns at a temperature of approximately 600°C. It is offset with an artificial smell, faintly resembling that of rotten eggs. This warns us against the explosive gas when a gas pipeline leaks.
Crude oil is a mixture of different substances and must first be ‘refined’ in a refinery—it must be broken down to its components. For this, it is heated at about 300°C in a distillation set-up. The individual substances evaporate at different temperatures. Petrol, used as fuel in many cars, becomes gaseous at temperatures between 35°C and 140°C, whereas diesel oil becomes gaseous at about 300°C. The different vapours are collected and cooled or liquefied. In this way, the individual components of crude oil are separated from one another and stored as diesel oil, kerosene, or petrol.
Bats cannot see very well. To orient themselves during their night flights, they emit ultrasounds. We cannot hear these sounds. The ultrasonic waves falling on obstacles or preys get ‘reflected’ back and reach the sensitive ears of bats. Thus, they come to know what all is present around them and where their prey is. This concept is also used in shipping to determine the depth of the sea using a device called sonar. It comprises a sound transmitter, a receiver, and a clock. The time difference between sending and receiving sound waves is measured, which is used to calculate the depth of the sea.
If you call out your name in the direction of a vertical, bare rocky wall, you will hear it again after some time. An echo comes because the sound waves are reflected back from the wall. When sound is produced in enclosed spaces, such as churches and gymnasiums, multiple reflections build up and blend together. This phenomenon is known as reverberation.
As the police car approaches us, the pitch increases, and when it moves away from us, the pitch decreases. When the car approaches us, the sound waves of the siren are ‘compressed’ more towards us, resulting in higher pitch. When the car is moving away, the sound waves get stretched; as a result sound fades away. This effect can be noticed only by an outside observer; the driver hears the same pitch of sound at all times. This phenomenon is called the Doppler effect, which is named after its discoverer.
Jets that fly faster than sound compress the air at the front. This forms a head wave. After a certain point of time, the pressure of the air gets discharged like an explosion. As a result, a loud bang takes place and we hear a loud sound. However, ultrasonic sounds are not audible to us. Bats and other animals use ultrasonic waves for orientation. Sound always propagates in the form of waves. Because of this reason we notice a change in the pitch of the siren of the vehicle passing us.
Normally, the light rays entering the eyes are bundled and refracted by the eye lens in such a way that they converge exactly on one point on the retina at the back of the eyeball. If the refractive power of the lens does not match the length of the eyeball, this ‘focus’ is shifted either in front of or behind the retina, and the vision becomes blurred.