ELECTRICITY AND MAGNETISM

If you ever hear you cloth crackle when you take them of, you will have made your own electricity. Electricity is a form of energy, carried by tiny particles of matter. When these particles are on the move, their energy can do lots of useful things. Closely linked with electricity is magnetism. This is an invisible force that makes things attract or repel each other, and can be strong enough to lift cars off the ground.

How does electricity move through a wire?
Electric currents are carried by particles called electrons, which are part of atoms. When a current flows through a wire, electron are jolted from atom to atom, carrying energy with them. Unlike static electricity, electric currents can only move through conductors, such as electric wires, and they always travel in a circuit. Conductor are metals and similar substances which have electrons that are easily dislodged.

Tag :electricity and magnetism

How does an echo work?
Sounds waves can bounce off solid objects, just as light waves can bounce off off mirrors. But because sound travels much more slowly than light, it can take several seconds to reach our ears. When it arrives, we hear it as an echo. Bats and dolphins use high-pitched echoes to find their food. Echoes are also used in sonar, a way of detecting submarines and mapping the seabed.

Calling back
If you shout at a wall, the sound will bounce back as an echo. To produce a good echo, the wall needs to be big and at least 25 m (80 ft) away.

Tag :echo

Overtaking sound
If the plane flies faster than the speed of sound, air begins to pile up in front of it. When this air slips out of the way, it suddenly expands, making a loud noise called a sonic boom. At one time, scientists thought it would be dangerous for planes to fly 'supersonically', but now planes like Concorde break the sound barrier every day. They usually do it over the sea, so the deafening sonic boom is not heard on land.

hearing faint sounds
You may not be able to hear a pin drop, but your ear can pick up some amazingly faint sounds. The faintest sound that most people can hear is about 10 billion times quieter than the sound of a live pop concert.

Tag :overtaking sound
Tag :faint sounds

Sound on the move
When sound comes from aboard a slow-moving boat, the sound waves spread out evenly through the water, where they move even more quickly than in the air. When the sound comes from a plane, the pattern of sound waves is quite different. This is because the plane moves much more quickly, 'catching up' the sound waves that it makes.

Sound in the air : Sound travels through the air at abut 330 m (1082 ft) a second. It move slightly faster on a warm day than on a cold one.

Underwater sound : Sound travels nearly four times faster in water than it does in air. This means that a fish will hear the boat before a person standing nearby it on land.

Chasing sound : Most passenger jets move at about two-thirds of the speed of sound. At this speed, a plane keeps catching up the sound waves in front of it, and race away from the one it leaves behind. These trailing waves make a low-pitched rumble as the plane flies away.

Fading out : As the sound waves travel outwards, their energy is slowly soaked up by the air. Eventually, they become too weak to be heard. This is why it is hard to make yourself heard a long way off, even if you shout.

Tag :moving sound

Things that makes sound

Rocket liftoff : 150-190 dB

Jet takeoff : 120-140 dB

Motorbike : 70-90 dB

Orchestra : 50-70 dB

Whispering : 20-30 dB

Rustling leaves : 10 dB

What's in a wave?
Closely spaced waves produce a high-pitched sound, widely spaced waves a deeper one. The sound is soft if the waves are shallow, and loud if they are deep.

Tag :sound makes
Tag :wave