Category Science

How does bridge made?

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

How does tunnel made?

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

How does radar work?

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

How does a remote control work?

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

What is a plant life cycle?

Like all living things, plants start their lives, grow, reproduce, and die. These steps make up a plant’s life cycle.

A seed plant begins when a seed germinates, or sprouts. A tiny root bursts out of the seed’s shell and pushes down into the ground in search of water. A tiny stem pushes up through the soil in search of sunlight. A new plant soon pokes its head above the ground.

The plant grows. Its roots take in water. Its leaves make food. After a time, the plant is fully grown. Small plants may become fully grown in a few weeks or months. A huge tree may take hundreds of years or more.

When a plant is ready to reproduce, it makes flowers or cones. The flowers and cones make pollen and eggs. The pollen and eggs join. Then new seeds form. Some seeds will be eaten by animals. Others will land in a place where they cannot grow. But some seeds will find a spot where the soil, water, and temperature are just right. These seeds will germinate, and the life cycle will begin again.

When a plant grows old, it dies. Its roots, stem, and leaves become part of the soil.

Picture Credit : Google

How Do Plants Make Seeds?

All seed plants have special seed-making parts. Most seed plants make their seeds inside flowers. The seed-making parts of a flower include long stalks. Some stalks have enlarged tips called anthers. Anthers make a golden dust called pollen. Other stalks have a sticky top called a stigma.

A seed starts to form when pollen from one flower falls onto the stigma of another flower of the same kind. The pollen travels down the stalk until it reaches a tiny egg. The pollen joins with the egg, which then grows into a seed.

Other seed plants make their seeds inside cones. There are two kinds of cones. One is small and delicate. It makes pollen. The other kind of cone is covered with wood scales and makes eggs. A seed starts to form when pollen blows from the delicate cones and lands on the scaly cones. The pollen and the eggs join. The scales close around the developing seeds. When the seeds are ripe, the scales open up again, and the seeds fall from the cones.

Picture Credit : Google