My Science School

Mmm! When it’s hot, cheese is stringy and gooey. You know cheese is made with milk. But how does milk get to the cheese?

In a cheese factory, cheese makers pour milk into big tanks. They heat the milk and add something called a “starter” to make the milk turn sour.

Next, they add an enzyme called rennin. The rennin makes the milk thicken and harden. The milk turns into a thick solid called curds and a thin liquid called whey.

 The curds are heated until they are firm and the whey is drained off. Machines salt the curd. It is then cut up and pressed into moulds. Most kinds of cheese are stored at a certain temperature for a period of time. This is called aging. Some kinds of cheese are aged for many months to get just the right flavor. When it has aged, the cheese is sent to the shop.

Add a couple of 2 spoonfuls of lemon juice and sugar to a half cup of whole milk. Stir. Let it stand for one minute. Now stir again. What happened? Did it get thicker?

Lemon juice is an acid. It sours the milk. But it also reacts with the fats in the milk. The milk thickens, just as it does when making cheese. The sugar speeds up this reaction.

How was cheese discovered? There is a legend about an Arab traveller accidentally making the first cheese. The legend says that, over 4,000 years ago, this traveller made a trip across the desert. He used a pouch made from a sheep's stomach to carry milk on the trip. Using animal parts like this was common then.

After a long, hot day, the milk turned into a watery, lumpy mixture. Rennin is found in the stomach of some animals. The desert heat and the rennin made the milk separate into curds and whey. Because the traveller was hungry, he ate the curds and whey and found it delicious.

 

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This bread does not rise very high, but you will see how yeast makes the dough expand. When you slice the bread, you will see the holes made from the gas bubbles.

You Will Need:

• 1 packet active dry yeast (12 ml) 60 ml warm water (like bath water, about


• 29 °C)


• 360 ml whole wheat flour


• 125 ml all-purpose flour 125 ml rolled oats


• 60 ml packed brown sugar


• 1 teaspoon salt


• 2 tablespoons vegetable oil


• 240 ml very warm water


• 1 egg


• a clean dish towel


• a greased bread tin

What to do:

1. Pour the 60 ml warm water into a small bowl. Sprinkles in the yeast. It should foam and bubble.


2. In a large bowl, mix the flours, oats, brown sugar, and salt.


3. Add the egg, oil, and very warm water to the large bowl. Mix.


4. Pour in the dissolved yeast and stir. The batter should be thick and sticky. Let it rest for 20 minutes.


5. Pour the batter into greased bread tin. Cover the tin loosely with a clean towel and place in a warm place, such as on top of the oven, to rise for about 35 minutes.


6. Ask an adult to preheat the oven to 92 °C or its lowest setting. Place the bread in the oven for 20 to 30 minutes. It should rise to twice its original height.


7. Ask an adult to turn up the oven to 175 °C. Bake 25 to 30 minutes until lightly browned.

 

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You can't spread a peanut on your sandwich, but you can spread peanut butter. What happens to peanuts between the field and the lunch table?

First, a machine digs up the peanut plants and shakes off the dirt. Another machine separates the pods, or shells, from the leafy tops. Then the peanuts go to a warehouse, where blowers remove the stems.

Rollers crack open the pods. Inside each pod are one, two, or even three peanut seeds. Another machine gently brushes the skins from seeds. A laser scans for rotten ones.

The remaining seeds are washed and roasted. They go into a grinder with salt, oil, sugar, and other ingredients. The mixture is ground. A conveyor belt moves clean, empty jars along while nozzles squirt peanut butter into the jars. The belt carries the filled jars to the next machine. This machine seals the jars and puts on the caps.

Now the jars are ready to be labelled and shipped.

Today, most foods are canned, frozen, put in jars, or packaged in some other way. These are called processed foods. Food is processed to preserve it, or keep it fresh longer. Processing also makes food easier to use. Peanut butter is a good example.

 

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You know where drinking water comes from, but where does the dirty water go? Down the sewer. Sewer water is filtered to remove solids before it is pumped into lakes and streams. This activity will help you see how water is filtered in nature and in a processing plant. But you must never drink your filtered water. It may look clean but it could still have germs in it.

You Will Need:

• an empty plastic bottle muddy water clean gravel


• a small jar with a mouth big enough to fit around the plastic


• bottle


• scissors


• cotton wool balls


• small, clean pebbles


• clean sand

What to Do:

1. Ask an adult to help you cut off the bottom part of the plastic bottle, about 18 centimetres from the cap.

2. Turn the top part of the bottle upside down and place it in the jar.

3. Push a wad of cotton balls into the neck of the bottle. Put in a layer of small pebbles, then a layer of gravel, then a layer of wet sand.

4. Pour some muddy water onto the sand and watch it drip through into the bottom of the bottle.

5. The water that filters through looks cleaner. What happens when you pour the water through the filter a second time? Does it look cleaner still? It is cleaner. Even so, it is not clean enough to drink. Do NOT drink it.

 

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Thirsty? Turn on the kitchen tap and fill a glass with water. Where does that water come from? Like other raw materials, water goes to a factory before it reaches your home.

When it rains, water seeps through the soil and rock a factory called a waterworks cleans the water for people to use.

First, waterworks pumps water from under the ground or from a river or lake. Then it filters the water. It removes tiny bits of dirt. The filtered water looks clean, but it may contain germs. Small amounts of chemicals are added to kill the germs.

The treated water flows to a pumping station sends the water to underground pipes called water mains. When you turn on the tap, water comes from the water main into your house.

Some cities pump treated water into water towers. These are called holding tanks. When water is needed, it flows to water mains on your street.

 

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A radio controlled clock has a radio inside, which receives a signal that comes from a place where an atomic clock is located. Such a clock may be synchronized to the time sent by a single transmitter, such as many national or regional time transmitters, or may use the multiple transmitters used by satellite navigation systems such as GPS. Such systems may be used to automatically set clocks or for any purpose where accurate time is needed. RC clocks may include any feature available for a clock, such as alarm function, display of ambient temperature and humidity, broadcast radio reception, etc.

One common style of radio-controlled clock uses time signals transmitted by dedicated terrestrial longwave radio transmitters, which emit a time code that can be demodulated and displayed by the radio controlled clock. The radio controlled clock will contain an accurate time base oscillator to maintain timekeeping if the radio signal is momentarily unavailable. Other radio controlled clocks use the time signals transmitted by dedicated transmitters in the shortwave bands. Systems using dedicated time signal stations can achieve accuracy of a few tens of milliseconds.

 

Picture Credit : Google

The Internet is a network of computers and certain other devices. In a network, all of the devices are connected. The Internet links tens of thousands of smaller networks. The Internet connects millions of computers in homes, businesses, and schools. People can bank, shop, watch TV, and do many other things on the Internet.

People can also send personal messages through the Internet. Such messages include e-mail (electronic mail), which is sent to and from an electronic “address.” Instant messages, or IM’s, work like back-and-forth conversations.

Many devices can access, or get into, the Internet. They include computers, mobile phones, and electronic game machines. A piece of equipment called a modem connects some devices to the Internet. Other devices can connect by using wireless technology, such as Wi-Fi or Bluetooth. Wireless technology allows communication between devices by means of radio waves sent through the air.

Information on the Internet exists as digital codes. Computers and other devices translate these codes into text, pictures, sounds, and videos. Digital codes are split up into smaller pieces called packets. The packets travel separately through the Internet. When the packets reach a computer or other device they are put back together into a single code. All these bits of information make up pages on the World Wide Web, the system of computer files on the Internet where much information is stored.

 

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The moon is a satellite. It moves on a set path called an orbit around the earth. Anything that travels around a planet is a satellite. Rockets carry artificial satellites into space. They circle high above the earth.

While artificial satellites circle the earth, they pick up radio waves from transmitting stations on the earth. Solar panels on the satellites collect sunlight to make electricity. They use this electricity to send the radio waves back to receiving stations. The receiving stations are often thousands of kilometres away from the transmitting stations.

Today, many hundreds of satellites whirl around the earth. Each one makes life easier for people on the ground.

 

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You're walking down the street when you suddenly hear your favourite song start to play. But where is the music coming from? As you look around, you notice that the person walking ahead of you is searching through his pockets. Of course the song is his special signal, letting him know that he has a call or a message on his mobile phone.

A mobile phone rings, vibrates, or plays music when it receives a signal. A display shows the phone number of the caller and possibly a message, too.

Some people carry mobile phones in their purses, briefcases, or pockets. Mobile phones use radio signals to carry their messages.

The service area for mobile phones is divided into groups called cells. Each cell has a radio transmitter. Signals are sent to the cell where the person using the mobile phone is. People who move around a lot still get their signals. The signals bounce from the transmitter in one cell to the transmitter in the next cell. This happens very quickly. Even if people are on a train while they are talking on a mobile phone, their conversation is not interrupted.

 

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When you call your friend on the phone, how does the sound of your voice reach them? You speak into the mouthpiece of your phone. The sound waves push on a thin sheet of metal called a diaphragm.

The diaphragm then vibrates. It presses against a small cup filled with carbon grains.

Electricity passes through the carbon on its way through the telephone wire. When the carbon grains are squeezed together, the electric current gets through easily. But when the grains are spread apart, only a little current gets through. So the vibrating diaphragm causes strong or weak pushes of electricity to travel through the telephone wire.

Your friend hears what you say through the earpiece on her phone. Inside it is an electromagnet a long coil of wire wound around an iron core. The strong or weak pushes of electricity reach the electromagnet. They cause it to make strong or weak pulls on another diaphragm. This diaphragm vibrates and makes sounds just like the ones your voice made. So your friend hears a copy of your voice-a copy made by electricity in a wire.

The first telephone was not like our phones today. You could speak into it but you could not hear the other person on it. Alexander Graham Bell first used it in March 1876. But by October of that year, Bell had the first two-way conversation on his invention.

 

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Pick up your telephone and call a friend. As you punch the buttons, signals travel on the phone line to your local telephone centre. That centre sends the signals to the phone centre nearest your friend.

While you are calling your friend, thousands of other people are making calls, too! And some people are using modems. Modems are machines that send information from one computer to another over phone lines. Other people use fax machines or e-mail to send letters over phone lines. Today, people are sending out more messages than ever, and phone lines help us to communicate across the world!

Microwave links and optical fibres can handle many thousands to millions of phone calls at the same time. Microwave links send signals as a radio beam. At the receiving station, the microwave signals are decoded. Optical fibres are long strands of coated glass. Cables made of these strands use lasers to turn messages into pulses of light. The light pulses are then decoded at the other end of the optical fibre. These cables can carry millions of telephone conversations and faxes, as well as computer information. They can also be used to carry television programmes.

 

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A shop owner is shutting up shop for the night. Before leaving, the owner sets the security alarm by punching a code into a keypad.

Many people use security systems to stay safe. Security systems use signals that tell them when to sound the alarm. Codes are entered in a keypad near the door. This turns the system on and off. If you forget to turn off the alarm when you return, the alarm will sound.

Many security systems use a motion alarm. A small transmitter inside the house sends radar waves into the room. The waves scatter and bounce around the room. They set up an invisible pattern. When someone enters the room, the pattern is upset, and the alarm goes off. A motion alarm will not work well if you have pets. When the pets move, they set off the alarm.

Another type of security system uses metal strips on the windows. When the window is closed, the metal strips touch each other. When the window is opened, this connection is broken and an alarm goes off.

Security signals keep us safe in many ways. Airports and courthouses use metal detectors to detect weapons. Many look like doorways. A transmitter on each side of the doorway sends out radio waves. Metal absorbs some of these waves and reflects them, or sends them back. The detector's transmitter then beeps, or signals that metal is there.

Libraries and stores prevent theft by placing coded targets on items. The target sets off an alarm at the exit if it has not gone through the check-out process.

 

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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.

 

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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.

 

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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