How does an electric motor work?

Most powered devices in the home contain an electric motor, which turns electric energy into movement. When an electric current passes along a wire in the field of a magnet, it exerts...

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....

How do we obtain fresh supplies of water?

An adequate supply of clean water is essential for life and for health. Water is often drawn from rivers, or may be pumped up out of the ground. Rainwater soaks into the ground and...

How do we obtain oil?

Oil is thought to have formed from the remains of organisms that died millions of years ago. Billions of tiny organisms lived in shallow water or in the surface layers of the oceans....

How is coal formed?

Coal is formed from the compressed remains of plants that lived in bogs 250— 350 million years ago. This was during the Carboniferous Period, when primitive animals first appeared on...

How is gold mined?

Gold is unusual 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....

How is mining carried out?

The earliest form of mining involved following seams of metal in tunnels driven into the rock. This method is still used today, usually in deep mines where other techniques would be...

How is a photograph produced?

Cameras work by focusing light in order to produce an image on a light-sensitive surface. Some cameras work by forming the image on light-sensitive film. Sometimes film uses dyes that...

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...

Where does rubber come from?

Natural rubber comes from a kind of tree that originally grew in South America. Its liquid sap, called latex, is drained from the tree by making cuts in the bark. The latex is collected...

How can television pictures be transmitted by radio waves?

Television cameras break a picture into electrical signals, separating them into three colors (red, blue and green) and turning them into coded messages. Sound is recorded and coded...

How does a telephone work?

Telephones transmit speech messages along wires by means of electrical signals. Telephones were invented as long ago as 1876. The handset of a telephone includes a loudspeaker and a...

What is the difference between a petrol and a diesel engine?

Engines that burn fuel inside them are called internal combustion engines. A petrol engine injects fuel into a cylinder and ignites it with a spark. The mixture of fuel and air explodes...

How do jet engines work?

Like rockets, jet engines propel an aeroplane with a stream of hot gases. Unlike rockets, which produce hot gas as a result of burning an explosive mixture, jet engines burn fuel in...

How did Roman numbering work?

In some ways, Roman numbering worked like the modem Arabic numeral system where, starting from the left, there are thousands, hundreds, tens and individual units. However, Roman numerals...

What is the metric system?

The metric system is a group of various units of measurement. Its name comes originally from the meter. It is a decimal system, which means that each unit is ten times bigger, or smaller...

Why do we need to use numbers?

Numbers are used to describe the amount of things. We can express numbers in words, by hand gestures or in writing, using symbols or numerals. When we talk about a number we use words...

How were calendars developed?

Calendars have been used for thousands of years. The early ones were usually based on the phases of the Moon and the movement of the Sun. We still depend largely on the natural movements...

What is Greenwich Mean Time?

In 1884 an international conference decided that the 0° line of longitude, or meridian, would run through the Royal Observatory in Greenwich, England. As you move to the east from...

How is time calculated?

The Earth spins on its own axis once every 24 hours, or day. The Earth orbits the Sun every 365 1/4 days, or year. Every 4 years we need to have a leap year with an extra day to make...

Why do we need to measure time?

People have always organized their lives by the passing of time. The earliest hunters had to hunt during the hours of daylight. When farming had developed, it was important for...

How does a gyroscope stand up?

A gyroscope is a heavy metal wheel made with ball bearings that reduce friction. Once the wheel is set spinning at high speed in an upright position, the force of gravity will try to...

What is a force?

A force pushes or pulls something in a particular direction. Isaac Newton was the first person to make a study of forces. He realized that when an object produces a force on something...

What is the sound barrier?

At sea level, sound travels though the air at around 340 m per second, and slightly slower at high altitudes. The denser the substance, the faster sound will travel through it. Sound...