My Science School

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

What is your home like? Are the walls made of brick, or wood, or concrete? Are the windows large or small? Does it have a wood shingle roof or a tile roof?

Today, most houses are made of wood, brick, and glass. The kind of materials used depends on the size of the house, its design, and the climate.

Many houses use a lot of wood. Wood is used to make the frame of the house and the frames between the walls. Sheets of wood are used for the floors and roof.

The roof is covered with tar paper and then tiled. In warm climates, ceramic tiles are used to keep the house cool.

In snowy climates, the roof slopes to let the heavy snow slide off.

On the outside, many homes use aluminium or vinyl walls because it doesn't need to be painted. They can withstand cold, hot, and windy weather. Bricks also make very sturdy walls and are usually easy to get. Bricks come in many colours, too.

Large glass windows let in lots of sunshine.

Gutters are made of aluminium or plastic. They keep the water running off the roof from leaking into the house.

 

Picture Credit : Google

Every day, workers in factories make the clothes we wear, the toys we play with, and the food we eat. The workers are the people on the assembly line and the people who pack and ship the products. But there are other workers involved in making products and food, too.

Does your cereal stay crispy in milk? People called food chemists develop and improve foods. They test new coatings or glazes to keep cereal crispy in milk. They add vitamins and minerals to make it healthier. And they test different ways of cooking and packing to improve the taste or quality.

Agricultural engineers help design the machines used to make a new breakfast cereal. They might work with the food chemists to decide how the cereal will be made.

Quality technicians test the food for freshness. They also make sure the taste and texture of the food stay the same during production.

Plant technicians work with the people who buy the ingredients. Quality ingredients are important to make quality food. Plant technicians also work on improving how food is shipped to shops.

 

Picture Credit : Google

When you ride your bike, you wear a helmet to protect your head. If you play football or other sports, you may wear helmets or shin guards made of plastic, But did you ever think you would wear plastic clothes?

Soon after plastics were invented, scientists learned how to make some of them into wearable fabric. For example, nylon is an artificial fabric made from plastic Nylon is lightweight and waterproof. That's why it is a popular fabric for outdoor clothes. When it's cold outside and the wind is blowing hard, do you put on a waterproof jacket? If you do, the chances are you're wearing plastic.

The lining of your jacket probably contains polyester. Polyester is another artificial material. It is often used in coat linings because it is durable and warm.

Many other things we wear are made from artificial fabrics. Look at your boots. Do the soles look like rubber? Today most “rubber" is made from nylon mixed with other artificial materials. Like rubber that comes from the rubber tree, it is good at keeping water out.

 

Picture Credit : Google

Let your imagination go. Snap brick after brick together and create a castle, or a spaceship. Children have played with building bricks for many years.

As you are making your cities and ships, do you ever wonder how plastic building pieces are made? They are made of a strong, tough, long-lasting plastic. Each building piece begins as a bunch of plastic pellets. The plastic pellets are heated to 230 °C. When they melt, they are like bread dough. Moulding machines press this "dough" into different shapes and pieces.

The parts fall into bins at the end of each machine. Robots collect the full bins. They are then labelled and placed in a warehouse.

Different departments put different building kits together. First, they order the pieces they need from the factory. Then, workers in each department seal the pieces in small plastic bags. The bags are sorted into boxes for the building kits. Other machines make the labels and boxes for each set.

For some model designers, work is play! Many get to play with plastic building bricks all day. Their job is to make designs for displays at toy fairs and exhibitions around the country. Sometimes these designs are over 2 metres high! Children love to play with toy bricks, too.

 

Picture Credit : Google

Look at your toys. What are they made of? Many toys are made of plastic. Plastic is easily shaped, and it lasts a long time. Hard plastic helmets protect us when we ride bikes or play sports. Rubber-like plastic is used to make balls. Soft plastics are used to make dolls. And plastic can be recycled to make long-lasting benches and picnic tables.

Plastic is not dug from the ground like metal ore. It is made from chemicals in crude oil. The chemicals in plastic can be heated so that they soften or melt. Then they are shaped into different items.

Sometimes, the chemicals are poured as liquid into moulds. Once they cool, the plastic becomes solid.

A softer, movable plastic called vinyl is used to make some toys. The moulds used to make these parts are spun around so that the vinyl clings to the inside walls. The parts harden as they bake in an oven.

 

Picture Credit : Google

Look around you. What objects do you see that are made of metal? The doorknob may be made of iron or brass. Your fork and spoon may be made of steel or silver. The ring on your mum’s or dad’s finger may be made of gold or silver. Metals are all around us. But where do they come from?

You can’t dig metal out of the ground. But the ore, or mineral, that metal comes from is found underground. Ore is made of metal joined with rocks. Ore is metal in its raw form.

To get metals out of the ground, miners first dig out the ore. The ore is taken to a factory where heat is used to separate the metal from the ore. This process is called smelting. The ores are dumped into a blast furnace and heated to over 1600 °C. The metals in the ores melt and pure liquid metal sinks to the bottom. The rest of the ore is waste material called slag.

The liquid metal is poured into moulds until it hardens. The bars of hardened metal are called ingots.

The ingots are ready to be rolled, pressed, or moulded into the shapes of the things we use.

 

Picture Credit : Google

The next time you drink your favourite juice, look carefully at the cup. Is it made of glass? Look at the windows in your house. They are made of glass. Marbles are usually made of glass, too. Where does glass come from? Actually It’s mostly sand!

Glass is made by mixing sand with chemicals. The mixture is heated above 1430 °C. Coloured glass is made by adding chemicals. To make the sheets of glass you see in windows, liquid glass is poured onto melted tin and pulled onto rolled when it sets.

Glass containers were first made about 4,000 years ago. The liquid glass was built up around a piece of clay. When the glass hardened, the clay was removed. About 2,000 years ago, someone discovered that a gob of liquid glass on the end of a tube could be blown into a hollow shape – like your juice glass!

Today, most glass items are made by machines. Gobs of liquid glass are pushed into moulds. Others are formed by people who use fire to heat the glass and make it soft enough to blow.

 

Picture Credit : Google