My Science School

 

 

 

Plastic is a very useful material but it also causes problems. Plastic does not rot away. So if plastic bottles or bags are dropped as litter they stay there for a very long time. Plastic litter spoils our environment.

 

 

 

 

 

A lot of plastic is thrown away.

Every year we throw away millions of tonnes of plastic. Most of it ends up in landfill sites and is buried under the ground. Most plastics do not rot or break down so they will be there for a very long time.

 

 

Continue reading "The problem with plastic"

 

Plastic can be used to keep us healthy. Hospitals use plastic because it is clean and safe. Plastic tubes are used in hospital to give us medicine. Blood is stored in plastic bags. We are given injections with plastic syringes.

 

 

 

 

 

These teeth are made from plastic.

As people grow older, they may lose their teeth. If this happens, they can have new ones made from plastic. Plastic teeth are hard perfect for chewing. They are shaped to look exactly like our own teeth. Even better, they will never need fillings!

 

 

 

This plastic hand looks real.

Plastic is used to make artificial parts of the body such as legs, arms, hands and ears. They are made to look real and are used to replace those lost in accidents or through illness. Artificial legs help people to walk.

 

 

 

 

 

 

 

 

 

Plastic can help us move again.

When we get older, our joints such as the hip or knee sometimes wear away and become very painful. An artificial joint made from plastic and metal can be used to replace the damaged joint so that people can move again without pain.

 

 

 

 

 

Some of our clothes are made from plastic. Fabrics made from plastic are easy to look after. They do not get dirty very easily or need much ironing. Plastic fabrics last a long time and do not lose their shape and become baggy.

 

 

 

 

 

 

 

These threads are made from plastic.

Plastic fabrics are made by forcing hot, runny plastic through very fine holes in a machine. The plastic comes out in thin fibres which are used to weave into fabric. Fibres made from plastic are called synthetic fibres. Sometimes synthetic fibres are mixed with natural ones such as cotton.

 

 

 

 

These clothes are made from plastic.

A special type of plastic material is designed to be fireproof. This material is worn by firefighters and racing car drivers. Before it is used, the material is rested with a white-hot gas flame to make sure that it will protect whoever wears it.

 

 

 

 

 

Tents made from plastic cloth keep out the rain.

Fabric can be made waterproof by adding plastic. Some fabrics are just coated with plastic on one side. Other fabrics are put in a bath of plastic paste so that the paste soaks into the fabric.

 

All wrapped up                                                 

Many of the things we buy are wrapped in plastic. The wrapping helps to keep things fresh. It can also tell us about the food we are buying. The words printed on a plastic yoghurt pot tell us what flavour yoghurt is inside.

 

 

 

 

 

 

If this bottle of water is dropped it will not break.

Plastic is a good material for packaging because it doesn’t break easily like glass. Plastic is very light compared with glass or metal. This means it is easier to transport plastic bottles to shops. Vans and Lorries need to use less fuel to transport plastic bottles.

 

 

 

 

Plastic bottles keep chemicals safe.

Plastic is waterproof and can be resistant to chemicals. Plastic can be used to package harmful chemicals. Even if the plastic bottle is dropped the chemical won’t spill because plastic is shatterproof.

 

 

 

 

 

 

 

 

 

The plastic wrapper keeps the food fresh. 

Plastic packaging is safe and hygienic. It helps to keep food fresh for longer so that less food is wasted. It protects the food from being damaged. The plastic film we use to cover foods is strong, waterproof, airtight and germproof.

 

Plastic can be made into foam. Foam is made by blowing bubbles of gas into melted plastic. Some foams have very tiny bubbles inside and others have bubbles that are big enough to see. Plastic foams are used in many different ways.

 

 

 

Plastic foam helps to keep things warm.

Plastic foam is a good heat insulator. This means it does not let heat pass through it. We use plastic to insulate our homes and stop heat being lost through the walls and roof. Buildings can be insulated by putting sheets of foam behind walls, floors or ceilings. We also use plastic foam to keep food and drinks warm.

 

 

 

 

 

Foam plastic is used to make furniture.

The soft furniture that we use in our homes is filled with spongy plastic foam. The air bubbles in the foam make it soft to sit on. Some foam gives off dangerous fumes if it catches fire. New furniture is made with foam that doesn’t easily burn.

 

 

 

 

Plastic foam helps to keep things safe from knocks.

Polystyrene plastic is used to package fragile objects that may easily get broken. The small pieces of polystyrene fit around an object and protect it against knocks. Polystyrene is strong but lightweight. It is used to make cycle helmets to protect our heads.

 

 

There are different ways of making plastic into the shapes we need. Many plastic objects are made using moulds so they are all exactly the same. This means that plastic objects, such as Lego building bricks, will fit together.

 

 

 

 

 

 

These bottles were shaped by a mould.

Plastic bottles are made by a method called blow moulding. A tube with a blob of runny plastic on the end is put inside a mould. Air is blown down the tube. The plastic inside the mould blows up like a balloon. It presses against the mould to make a hollow bottle shape.

 

 

 

 

 

 

Hand-shaped moulds are dipped in plastic.

Plastic gloves are made by dip-moulding. A solid hand-shaped mould is dipped into hot liquid plastic. It comes out covered in a thin layer of plastic. When the plastic is set and dry the finished glove is peeled off the mould.

 

 

 

 

 

 

Plastic is squeezed through a hole to make a drinking straw.

Drinking straws are made by a method called extrusion. Hot, runny plastic is forced through a hole. As the plastic pushes out through the hole, it forms into a tube shape, just like icing piped onto a cake.

 

 

 

 

There are hundreds of different kinds of plastic. Some plastics are hard and others are soft and bendy. Plastic can be thin, thick, coloured or see-through. Plastic is a very useful material and we use it in many different ways.

 

 

 

 

 

 

 

 

These things are made from different types of plastic.

There are two different groups of plastic. The plastics in one group melt when they are heated, and become solid again when they cool. These groups of plastics are used to make bottles and clothing. The other groups of plastics do not change shape when they are heated. They are used to make objects such as saucepan handles and CDs.

 

 

 

Continue reading "What are the different types of plastics?"

 

 

 

 

 

Oil is drilled and pumped out of rocks in the ground. Sometimes oil is found in rocks under the sea. A platform called an oil rig is used to reach under-sea oil. It stands or floats in the sea and drills the oil from the rocks.

 

 

 

 

 

 

Oil is taken here to be made into different things.

Crude oil is taken to an oil refinery by a pipeline or huge oil tanker (ship). The refinery is like a huge factory where the oil will be separated into different things. Care must be taken when transporting oil. If the oil spills it can damage the natural environment.

 

 

 

 

 

 

 

The oil is heated and separated in a big tower. The oil is separated into different chemicals by heating it in a huge tower. As the oil gets hotter the different chemicals in it boil, turn into gases and separate out. When the separate gases cool down again, they turn back into liquids. The liquids are collected. Naptha is one of these liquids. Naptha is turned into plastic called polythene, which is used to make many different plastics.

               Around 150 years ago, people did not have plastic things. Now plastic has become an important part of our everyday lives. Hundreds of different types of plastic have been invented. Think about how many plastic things you use each day.

 

 

 

Cotton plants were used to make the first plastic.

The first plastic was made in 1862 from cellulose, which is a material found in plants. Alexander Parkes used cotton to make plastic called celluloid that could be moulded into many different shapes. This first plastic was used to make ornaments, cuffs and collars.

 

 

 

 

The telephone here is made from coal tar.

In 1907, a new plastic called Bakelite was made from coal tar. This plastic could be moulded into any shape and it would not burn, boil or melt once it had set hard. It was used to make telephones and radios.

 

 

 

 

 

 

This surfboard is made from a new strong type of plastic.

New plastics have been invented that are strong, durable, light and flexible. They are used to make sports equipment such as windsurf boards, ropes and bullet-proof vests.

 

 

 

                Plastic is a man-made material. It is an amazing material that is used to make many different things. Every day, all over the world, people use or wear things made from plastic.

 

 

 

 

 

 

               Most plastic is made from oil. Crude oil is the raw material that most plastics are made from. Oil is a fossil fuel. It is made from the remains of tiny aquatic plants and animals that lived millions of years ago. Today, oil is found in rocks that are deep under the ground or under the sea.

 

 

 

 

Continue reading "What is Plastic?"

               CAT scanner is the most modern instrument used as a medical diagnostic tool. It is in fact a modified technique of using X-rays for diagnostic purposes. It can detect the diseases of brain, kidney, liver, abdomen etc.

               The word CAT is an abbreviation of Computerized Axial Tomography. CAT scanner was invented in 1972 by a British electronic engineer Godfrey Hounsfield and a U.S. physicist Allan Cormack. For this invention both these scientists were awarded jointly the Nobel Prize for medical science in 1979.

               CAT scanners are of two types: head scanner and body scanner. Head scanner is used to diagnose brain diseases. With this, brain tumour, brain haemorrhage, clots in the brain etc. can be identified. Body scanner is used to diagnose different diseases of stomach, liver, chest etc.

               A CAT scanner consists of an X-ray source from which the rays can be allowed to fall on any part of the body. Opposite to the X-ray source, there are many detectors which receive information from various body parts. In the middle, there is a stretcher for the patient. It is operated by a motor. Detectors are usually made of sodium iodide, calcium fluoride and bismuth germinate. Modern equipments consist of up to 300 detectors.

               X-ray source produces pulses of X-rays in an interval of 2 to 3 seconds which fall on the different body tissues. On passing through the different tissues they carry the information to the different detectors. These detectors are connected to a computer. For example, a scanner with 300 detectors will send 300 x 300 = 90,000 signals to the computer after receiving 300 X-ray signals. These signals are analyzed by the computer and projected on the TV screen in the form of a picture. The computer is connected to a television screen. The signals coming from the computer are in accordance with the density variations of the body tissues. These signals are projected on the TV screen in the form of the body organ. This picture gives the clue to the disease. The picture from the TV screen is recorded permanently on a bromide paper. Doctor can know the disease from this photograph, and can give the proper treatment.

               Another advantage of CAT scanner is that the doctor can check whether the treatment being given to the patient is effective or not. This information is obtained by scanning the body of the patient repeatedly.

               Nowadays almost all hospitals, nursing homes have CAT scanners equipped with the latest technical knowhow for diagnosis of different diseases. 

               You know that each electrical plug has three pins. These three pins are connected to three wires which in turn are connected to an electrical appliance. Two of these three pins are of the same size while the third pin is thicker than the other two. It is usually connected to a green wire. This is known as the earth wire. Do you know what the function of the third pin is?

               The third pin and the third wire (green) in an electrical lead carry no current when everything is normal. One end of this lead is connected to the body of the electrical appliance and the other end is connected to a metal plate buried in the ground. In fact the third pin connects the body of the electrical appliance to the earth. This is known as electrical grounding. It is a precaution in case a live wire accidentally comes into contact with the metal frame of the appliance.

               Sometimes the electrical appliance may develop a fault which makes the electricity flow to the metal casing. Then a person touching it receives an electric shock. The electricity flows from the casing, through the person, into the ground. The shock felt by the person depends on the intensity of current. If, for example, the person has wet hands, the shock experienced would be of a greater intensity, because wet skin conducts electricity better than dry skin. 

Continue reading "Why are there three pins in a plug? "

               Pulley is one of the earliest devices used by man to hoist or shift heavy loads and raise water from wells. It was developed from the concept of wheel—the most wonderful invention made by primitive man.

               Pulley is also a wheel made of wood or metal with a groove cut around its rim. It is fitted with a string or rope around its groove. Pulley turns on axis or an axle and is fixed in a framework called a block.

               Do you know how heavy loads are lifted by pulleys? There are several types of pulley systems. For example in a single fixed pulley the load is attached to one end of the string running round the groove of the pulley and the force is applied at the other end of the rope. In this system the force applied is equal to the weight lifted but it has the advantage that force is applied in the downward direction which is easier than pulling up. Single pulleys are used in drawing water from wells etc.

               The second system is of a single movable pulley. In this system weight is attached to the movable pulley. A string runs over this pulley whose one end is fixed and the other end passes over a fixed pulley. The second pulley is used to apply force in the downward direction. If both the pulleys are frictionless, then the force applied on the movable pulley becomes just double than the actual force applied. This has a mechanical advantage equal to two. This type of pulley is used in the cranes. Sales in boats are raised and lowered with the help of movable pulleys.

               To get more mechanical advantage, several pulleys are used together in many combinations. For instance, in three pulley system, the upper block is fixed and the lower block is movable. A string runs over all the pulleys alternately on movable and fixed pulleys. The weight to be lifted is attached to the lower block. When the number of pulleys is same in both the blocks, the end of the string is tied to the upper block and passed onto the pulleys. If the number of pulleys is not equal in both the blocks, the string starts from the lower block and it is repeatedly turned over the pulleys and is taken up. In fact the weight of the load to be raised with a pulley depends on the number of wheels and how they are connected together. 

               Whenever any airplane gets crashed, efforts are made to recover its black box. When Jumbo Jet Kanishka of Air India got crashed, its black box was searched and recovered from the deep sea by a robot. Do you know what this black box is and what information it gives regarding the cause of the plane crash?

               Most of the airplanes on International flights have been using two important instruments since 1960. These instruments are known as Digital Flight Data Recorder and Cockpit Voice Recorder. These instruments are enclosed in two steel boxes separately to provide safety. These two enclosed boxes are called black box. These steel boxes are made of such insulating material which can withstand a temperature of 1000°C upto half an hour. They are also not affected by shocks. The tape which is used in these instruments is made of stainless steel which is not affected by sea water for two days. Flight Data Recorder is placed in the rear of the plane while Cockpit Voice Recorder is put in the cockpit of the plane.

               Flight Data Recorder is a multi channel recorder. Its tape is made of stainless steel which is very elastic. Its length is about 6000 ft which can record the data of a 25 hours flight. It records the temperature of the plane, its velocity and direction of flight, sound of the engine, readings of various instruments, wind velocity etc. In all it can record 64 parameters. These parameters provide a clue about the accident of the plane. It takes several weeks to decode and analyze the data recorded on the tape.

               Cockpit Voice Recorder is a type of tape recorder in which a magnetic tape runs. This records the conversation among the crew members in the cockpit. It also records the sound of explosion. These voices come to the recorder with the help of a microphone fitted in the cockpit. This keeps a record of the events which have occurred during the last half an hour. Prior information is washed off automatically. In this way this tape is used repeatedly.

               When an airplane meets with an accident, efforts are made to recover these instruments to know the causes of the accident. Recorded information is analyzed and the reasons of accident are established. In fact, this electronic equipment records details of the flight. 

               We know that our Earth is ball-shaped. If we continue digging at a particular place, we would notice that the temperature goes on increasing with the increase in depth. Before we discuss the subject we must have an idea about the three main layers of Earth. The top, the second and the third. The top or first layer of Earth is a thin crust of hard rocks that floats on the second thicker layer of rock called “mantle”. This is so hot that most of its rocks are partly melted. The third layer is made of hot liquid iron. In fact, at the core it is extremely hot. The temperature can be imagined from the huge amount of energy which is released when the volcanoes erupt.

               Around the year 1800 some Italian scientists performed certain experiments, to make use of Earth’s internal heat. They dug a hole in the earth through which jets of hot steam and pungent gases shot out. These blow-holes are a sign of volcanic activity taking place under the ground. The gases they release into the air come from molten rocks known as magma which lies at depths ranging between 20,000 and 80,000 metres or more.

               Scientists found boric acid in these vents. An industry was set up to extract this chemical substance in Italy in 1818. Later it was discovered that the power of these gas jets could be harnessed for other tasks, including the generation of electricity. For the first time geothermal electricity was generated at Landarello in Italy in 1904.

               The internal heat can be used to produce electric power in four ways: dry steam, as at Landarello; hot water as at Reykjavik, in Iceland; low temperature areas in basins of sedimentary rocks, containing water between 40°C and 100°C which is used for agricultural purposes such as heating glass houses; and high pressure zones found by petroleum drilling deep in sedimentary basins. The natural gas released from the earth in particular localities (generally near deposits of mineral oil) is used as fuel and also as a source of energy.

               In the last few years the scientists have developed several mechanisms for the optimum use of Earth’s internal heat. They have been trying further to develop such instruments further that could be used to utilize the earth’s geothermal energy effectively.