What are explosives?

Explosives are substances that release a very large amount of energy in a short time when they burn. They all contain a fuel plus an oxidizer, which is a substance containing sufficient oxygen to burn the fuel. Explosives do not need air to explode, because they contain their own oxygen, and so they can burn in confined spaces or even underwater. Some explosives, such as those in a cartridge detonator, explode violently when hit or heated. Others only cause a violent explosion when confined in a gun barrel or a hole drilled in rock for blasting.

Gunpowder, the first ever explosive, was invented in China over 1,000 years ago. Large amounts of modern explosives are commonly used in quarrying and mining, as well as for munitions.

What is electricity?

Electricity powers our lights, heating, electronic appliances such as computers and television, and a host of other essential services that we take for granted. However, electricity has much more important aspects because it is the force that holds together the molecules and atoms of all substances.

The type of electricity that is most familiar to us is electrical current. This is the flow of electrical charges through a substance called a conductor, such as a metal wire. This flow happens because some of the negatively charged electrons circling the nuclei of the conductor's atoms are held loosely. The electrons can move from one atom to the next, producing an electrical current.

Energy can no be created. An electrical generator is simply a means of converting mechanical energy into electrical energy. In its simplest form, a generator spins coils of wire in a magnetic field, causing the flow of electrical current in the conducting wire. The power to spin the generator comes from other forms of energy. This energy might be stored energy in fossil fuels such as coal or oil, hydroelectric power from dams, wind power from turning huge windmills, or nuclear power produced by the radioactive decay of elements. In all these cases, one form of energy is simply converted into electrical energy.

What happens to our waste?

The huge quantities of domestic and industrial waste that we produce cause a major environmental problem. sometimes waste is buried in vast landfill sites, which are often old quarries. Alternatively, waste can be burned or in some cases recycled.

Waste from our toilets, baths and washing machines is collected in sewers and carried to a treatment plant. Bacterial action breaks down solid waste into a harmless form, and the waste is stirred in huge pools while this process takes place. after treatment, purified water is run off and can safely be drained into rivers. The solid material remaining is usually processed into fertilizer, after further treatment to make sure it contains no dangerous microbes.

How is gold mined?

Gold is unsuall because it is found in its metallic form, rather than as a chemical compound. Metallic gold, which is easy to identify and shape, has been mined for thousands of years. Most gold is found in what are called alluvial deposits. They consist of river mud containing tiny particles of gold washed out of rock over thousands of years. Water currents are used to wash away the mud and gravel, leaving the heavy gold particles. Gold is mined in many parts of the world, but most modern gold suppllies have come from countries such as South Africa and Russia.

Gold does not tarnish, and this makes it very valuable. It is used mainly for the manufacture of jewellery and for coating electrical contacts. It is also a very good conductor of electricity.

What is Greenwich Mean Time?

In 1884 an international conference decided that the 0 degree line of longitude, or meridian, would run through the Royal Observatory in Greenwich, England. As you move to the east from the Greenwich meridian, the time is one hour ahead of Greenwich Mean Time for each degree you move. If you move to the west, time is one hour behind for each degree. Midday is the point where the sun is highest in the sky, whichever time zone you are in.

The amount of daylight varies with the seasons, so daylight-saving time, or summer time, was introduced to make maximum use of daylight hours. In the northern hemisphere, clocks are reset one hour ahead in spring and one hour back in autumn. In the southern hemisphere the seasons are reversed.

What type of materials are plastics?

Plastics are synthetic materials that consist of long chains of molecules called polymers. Whe nthe chains a positioned in a long the plastic is rigid. When the polymer molecules are tangled tpgether, the plastic is soft and flexible. All plastic can be moulded under pressure into complicated shapes. Thermoplastics melt when they are heated, and this means that they can be remelted at any time. There are other forms of plastic, known as thermosetting plastics, which cannot be remelted.

The majority of plastics are made from synthetic resins, which are usually derived from oil. Other types come sources such as coal or wood. As they do not conduct electricity, most plastics are excellent insulators, so are widely used in electrical wiring.

The main disadvantage of plastics is that they are very slow to break down,causing serious environmental problems when discarded.

What are silicon chips?

A silicon chip is a tiny wafer of silicon (a semiconductor) on which a complete electronic device can be produced. An image is produced photographically and etched into the chip, but it differs from a printed circuit in some important ways. The chip is often microscopically small and contains huge amounts of "wiring". More importantly, part of the process allows other devices to be produced in the manufacturing process, such as tiny resistors and capacitors. So a silicon chip, or integrated circuit, which measures just a few millimeters across, is a complete electronic device.

How is natural gas obtained?

Natural gas is widely used to supply energy for domestic use and for industrial processes. It was formesd millions of years ago by the same process that produced oil. Gas flows or is pumped by boreholes, often mixed with air and water. Then gas is separated and passes through a refinery. Some of its constituents, such as propane and butane, are removed and liquified so bthatn they can be pumped into cylinders and used as fuel. Liquified gases held under presure can be carried all around the world in specially constructed ships.

The remaining gas, which consist mainly of methane, is pumped along pipelines for domestic use. Methane has no smell, so a strong-smelling additive is used to make people aware of gas leaks.

Who invented the first steam engine?

During the first century AD, a Greek inventor and mathematician called Hero of Alexandria produced a device that later led to the development of modern turbines and jet engines. Hero's device was a hollow water-filled ball mounted on a swivel. Two nozzles stuck out of opposite sides, pointing in different directions. When the ball was heated, steam shot out of the nozzles, causing the ball to spin rapidly.

Hero failed to see the practical use of this device and regarded it as an interesting toy. He went to invent several mathematical formulae, one of which is still used for calculating the area of the triangle.