Science

Acid: a sharp or sour-tasting substance.The degree of acidity is measured by its pH. Anything with a pH below 7.0 is an acid Alkali: the opposite of an acid. A substance having a...

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...

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 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...

What is the Doppler effect?

You will have noticed that as a car travels quickly towards you, the sound of its engine gets higher, then becomes deeper after the car has passed by. This is called the Doppler effect....

What is an echo?

Like light, sound can be reflected from certain surfaces. Hard surfaces such as rock or the side of a building reflect sound well; as the sound bounces back you hear an echo. The delay...

What is sound?

Sound is a form of vibration passing through the air or some other material. Sound travels in the form of waves but, unlike electromagnetic waves, sound waves cannot pass through a...

What are lasers?

Lasers are devices that produce a narrow beam of very strong light. Lasers amplify light by causing photons to be bounced back and forth in a substance (solid, liquid or gas), which...

What are isotopes?

The nucleus of an element normally has a fixed number of protons and neutrons. Some elements exist in different forms, however, with varying numbers of neutrons in their nuclei. A...

Radioactive healing

In a nuclear reactor, uranium or plutonium undergoes fission, releasing huge amounts of energy. Graphite rods absorb some of the energy and prevent the reaction 'running away' and causing...

What is a nuclear reactor?

A nuclear reactor is used to control nuclear fission. In most reactors, uranium is encased in metal tubes that are inserted into the reactor. The tubes are surrounded by a moderator...

Atom bomb

The atom bomb is such a powerful weapon that it has only been used in anger twice, near the end of World War II, and even testing has now been abandoned. The technology to produce atomic...

How do nuclear power stations work?

Once nuclear fission takes place inside a nuclear reactor, the chain reaction has to be controlled, or moderated. The reactor's core of uranium is surrounded with a substance that slows...

How is nuclear energy produced?

Nuclear energy is produced by changes in the nucleus of the atom of a radioactive element such as uranium or plutonium. This process is called nuclear fission. The nucleus is split...

How do computers work?

A computer is a device for processing information very rapidly and accurately. It processes words, pictures, sounds and numbers, and some computers can make billions of calculations...

What is a printed circuit?

Any modern electrical device requires a huge number of connections to join together all the small components needed for it to work effectively. At one time these connections were made...

How does radio communication work?

Radio signals are transmitted using a carrier wave. A radio transmitter changes, or modulates, this radio wave in order to convey information. In AM radio the height of the carrier...

What are radio waves?

Radio waves form part of the electromagnetic spectrum. They are not part of the visible spectrum of light, and they have even longer wavelengths than infrared radiation. Radio waves...

How does a compass work?

The magnetized needle of a compass tries to align itself towards the Earth's field of magnetic force. The magnetized needle balances on a pointed pin or floats on oil to allow it to...

Is the Earth a magnet?

The Earth is actually a huge magnet, with a magnetic north and a magnetic south pole. These poles are not quite the same as the true geographical poles, and they wander about slightly....

How does electricity produce heat and light?

A good conductor such as copper has only very low electrical resistance. It does not get very hot when electricity flows though it, making copper suitable for household wiring. Other...

How do batteries work?

Batteries produce electricity by means of chemical action. A battery contains two different conductors, or electrodes. Usually, one of these is the metal case of the battery. The...