Category Kids Queries

Thanks to bridges, rivers and lakes will not interrupt a journey. People build bridges to make it easier to cross rough land or water. There are thousands of bridges in the world, but only five basic kinds: beam, arch, suspension, cantilever, and cable-stayed bridges.

Do you think bridges could be made out of glass? Inventors are working on this idea now. Concrete used in bridges is worn down by salt, ice, and wind. The steel used to make the concrete stronger often rusts. But a special glass called fibreglass is very strong. When glass fibres are held together by a type of “glue” ice, and wind. The steel used to make the concrete stronger often rusts. But a special glass called fibreglass is very strong. When glass fibres are held together by a type of “glue” called resin, they become stronger than steel or concrete. Fibreglass is also lightweight and can be easily shaped.

Beam bridge: This can be made of wood, steel, or concrete.

Arch bridge: A beam bridge can break easily in the middle. But a curving arch helps to carry the load on the bridge.

Suspension bridge: The roadway is suspended, or hung, from long steel cables. This type of bridge can be much longer than other types.

Cantilever bridge: One or more independent beams joined by a centre span make a cantilever bridge.

Cable-stayed bridge: This is one of the newest kinds of bridge designs. It takes less concrete or steel than a beam bridge. And it fits across narrow rivers better than a suspension bridge.

Picture Credit : Google

People have been using bridges to cross water for thousands of years. The earliest bridges were tree trunks. A tree growing near the bank was chopped down so that it fell across the river. Then people walked across on it. In the jungles of South America, for a long time people have made bridges out of the vines that grow there.

The ancient Romans built arched bridges out of stone. Many of them are still used today! Some bridges are still made in the same way,

Bridge-builders build strong columns, called piers, on each side of the arch. Then a strong frame is made out of wood between the piers. The arch stones are laid on top of the frame. Each stone is wedge-shaped-it is wider at the top than at the bottom. The last stone, which fits in the middle of the arch, is called the keystone. When the keystone is pushed into place, the wooden frame is taken away.

The arch will then stay in place by itself. Each stone is pressing against the next, so they hold one another up.

Picture Credit : Google

You are building a road but a mountain is in the way. Could the road be built over the mountain? That would be rough travelling. What about going around? That would take longer-to build it and to drive on it. What about digging a tunnel? A tunnel is the shortest route, and there are many ways to build one.

Tunnels built through hard rock are usually blasted. Workers use explosives to blast each section of rock. Then they build supports in the newly opened part of the tunnel to keep rock from falling in.

Huge boring machines tunnel through clay or soft rock. As steel tubes dig through the ground, the machine “swallows” the earth and rock. The earth is dumped at the back of the machine the tunnel opening where trucks can haul it away. Reinforced concrete or steel is used to make the floor, walls, and roof of the tunnel.

Cut-and-cover tunnels are built close to the surface. Workers dig a deep trench. Then they build a floor, walls, and roof of reinforced concrete. When the concrete has hardened, the area around the concrete is filled to street level.

The mountain is no longer in the way. You simply drive right through it.

Picture Credit : Google

Aeroplanes get into traffic jams just in the same way cars do-especially around busy airports. But people called air traffic controllers know where each plane is located. They use radar to help them direct air traffic.

Radar allows the controllers to find planes that are too far away to see. And radar does this at night and in rain, fog, or snow.

A radar set sends out radio waves. When the radio waves hit a flying plane, or even a raindrop, they bounce back to the radar set. This makes spots of light appear on the tracking screen.

The moving spots of light tell a controller where the object is. They know how far away it is, how high it is, how fast it is moving, and which way it is going. Then the controllers can direct the air traffic, much as police officers direct road traffic. They make sure each plane follows a safe path when flying, taking off, or landing.

The planes have radar sets, too. The pilot can look at the radar to make sure that no violent storms or other planes are dangerously close.

Picture Credit : Google

Have you ever tried to switch channels on TV when someone stood in the way? Nothing happened. Why not? The transmission of the signal was blocked. The signal from the remote control hit someone’s body instead of the TV.

Remote means “far away”. When you use the remote control, you are controlling the TV from a distance. The remote control uses an invisible type of light called infrared light to send a signal to a receiver on the TV.

The buttons on your remote control send different codes to the TV. The code consists of long and short flashes of infrared light. When you press a button, the remote control sends the code for that button to the receiver in the TV. The TV “sees” the signal and carries out the command.

Some toy cars use a radio remote control to guide their movements. Turning knobs or moving levers sends a signal to the car to go forwards or backwards, or turn left or right. A garage door opener uses a radio wave to send its signal. Different openers have different frequencies so that you won’t open your neighbour’s garage door by mistake.

Picture Credit : Google

Did you know that the pictures on TV are a jumble of red, green, and blue dots? When you sit across the room, the dots blend into the images you see.

At the television station, a camera records the picture and sound from the scene you are watching. Mirrors in the camera split light from the scene into red, green, and blue. A tube in the camera changes the light to radio signals. The television station broadcasts the programme to your home.

TV antenna, cable, or satellite dish A receives many broadcast signals at once. The television tuner is used to select the signal for the TV channel you want to see. The tuner passes this signal to the amplifier. The amplifier separates the sound from the pictures.

The sound goes to the speakers. The picture signal is sent to a decoder. The decoder sends the signal to the electron guns. There is one gun for each colour red, blue, and green. The electron guns zip across the screen in weak or strong bursts of light. These bursts form the picture you see on the screen.

Picture Credit : Google