current science Archives - Champak Magazine

Make A Sundial

A sundial is a device that tells time using the position of the Sun, or more precisely using its hour angle, or sometimes its altitude.

Things you need:

• Mount Board • A Sweet Box Protractor Ruler Glue Box Cutter Sketch Pen White Paper

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Telling Time

A sundial is a time keeping device that measures time using the position of the sun. The earliest sundials were used by ancient Egyptians around 3500 B.C.

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Do:

Wrap your box with white paper. Draw a base line at the bottom.

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Mark out points 15° apart using a protractor, starting from the base line.

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Draw lines from the center through these points. The sundial’s face is now ready.

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To make the gnomon cut the shapes as shown from mount board.

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Fold the strips in an ‘L’ shape and paste them on either side of the triangular piece.

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Paste the gnomon along the middle line of the sundial and label as shown on the next page.

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Think about:

Water clocks

Since sundials can’t be used indoors or after sunset, the Greeks, Romans and Egyptians used a water clock or a clepsydra (klep-sid-ra). These devices would measure time with the help of a stream of water flowing from a container. The water would fill another container with markings which would tell what time it was. With time, water clocks became more complicated and hourly intervals would also be marked by chiming bells, moving figurines etc.

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Find Out:

Jantar Mantar

The world’s largest sundial is at the Jantar Mantar in Jaipur and is called the Samrat Yantra. It was built by Sawai Jai Singh between 1727 and 1734. The Samrat Yantra stands 27 meters tall and is accurate up to two minutes of the actual time.

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See:

How to use the sundial

You can adjust a sundial with a magnetic compass or a watch. For it to work properly it needs to face north. This is because the sun moves from east to west. If our sundial faced east or west, the shadow of the gnomon (the time-telling edge) would fall under it. By aligning the sundial on the north-south axis with a compass, we can get the longest shadows. Once placed a sundial must not be moved. The sundial can also be calibrated with a watch by simply placing the sundial in such a way that the time according to your watch is the same as what the sundial reads. For example, if the time according to your watch is 1:00 p.m., adjust the sundial in such a way that the gnomon’s shadow touches the 1 p.m. line.

Since sundials tell the local time according to the sun, it may be off from the current time.

DISAPPEARING COLOURS

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1. Use the lid to trace a circle on the white paper and cardboard. Cut both of them.

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2. Using a pencil and scale, divide the circular sheet of paper into 6 equal parts as shown, and colour each in a different colour: purple, blue, green, yellow, orange and red.

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3. Glue the paper to the cardboard.

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4. Make a small hole in the centre of the disc and poke a skewer through it. Hold the skewer and spin the colour disc.

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See

As you spin the disc fast, you will see that the different colours start to merge and appear as one colour (white).

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Think about

Why do the different colours combine and appear white?

First, the colours combine and appear as one because of the way our eyes read moving images. When the disc spins, our eyes cannot register the colours separately, and hence perceive them as one. Second, the colours combine and appear white because of the composition of white light. All types of light travel in waves of different frequencies. Our eyes can only see lights that travel within a specific range of frequency called the visible spectrum. This spectrum consists of lights of different colours: red, orange, yellow, green, blue, indigo, and violet. When these colours are combined or travel together, they fuse into one to form white light. So, when the disc spins, the colours combine and appear white.

Let’s Find Out

How are rainbows formed?

The (white) light that we receive from the sun is composed of several colours. When a beam of sunlight passes through rain drops (which is why we see rainbows mostly during the monsoon), at a certain angle on its way down, it splits into the different colours it is composed of, thus forming the rainbow.

Photo credit: Pixabay.com

MAKE A PARACHUTE

Stuff

Plastic cover/ bag
String
Scissors
Scotch tape
Your favourite action figure (should not be too big) or a small stone

1. Using a large circular lid or any circular object, trace a circle on the plastic cover and cut it out.

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2. Mark eight points along the edge of the circle as shown. The points should be equally spaced.

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3. Take eight strings of equal length (each about 50 cms long). Stick one end of each string to the markings on the circle.

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4. Tie all the loose ends of the strings into a knot and attach it to your action figure or stone using tape.

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See

When you drop the action figure or stone from a height, it lands gently on the ground as the parachute opens up and slows down the fall.

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Think about

How does the parachute slow the fall?

An object falls because the force of gravity pulls it down towards the ground. When the parachute attached to the object opens up, its surface area increases. Thus, it traps a large amount of air under it, which offers resistance to the falling object. Now, there are two forces that are acting on the object: gravity and air resistance it is similar to someone trying to you push you back when you are trying to move forward). The air resistance caused by the air trapped under the parachute is greater than the gravity acting on the object, and hence the fall is slowed down.

Let’s Find Out

What are the uses of a parachute?

A parachute is used to slow down the jump of people or fall of things from heights, ensuring they can land safely: soldiers use parachutes to land safely after jumping off planes; fighter jets use parachutes to slow themselves down after they land on aircraft carriers; packets of food and medicines are tied to parachutes and dropped from planes into areas affected by natural disasters.

HOW TO DRINK SALTY WATER

Stuff

A small cup (glass or steel)
A big mixing bowl
A small, smooth stone
Plastic wrap
String or scotch tape .
4 cups of drinking water
2 tablespoons of salt

1. In the big mixing bowl, pour 4 cups of water and add 2 tablespoons of salt to it. Mix well till the salt dissolves.

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2. Place the empty small cup in the centre of the bowl as shown. Make sure the salt water does not get into it.

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3. Take the plastic wrap and cover the bowl. Seal the edges with string or tape.

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4. Place the stone over the plastic wrap directly above the small cup so that the wrap slopes towards the centre. Now, place the bowl under the sun for a few hours.

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See

In a few hours, water droplets will start forming beneath the plastic wrap. These droplets will slide towards the centre of the bowl and collect in the cup. If you drink this water, you will notice it does not taste salty.

Think about

How does salt water become drinkable?

Water can exist in three states: solid, liquid and gas, depending on how much energy the water molecules have. When the bowl is placed under the sun, the water particles at the top of the water surface gain energy from the sun and turn into gas (water vapour). This process is called evaporation. As the water vapour is blocked by the plastic wrap, the water particles begin to lose energy and transform back into water and collect beneath the wrap as water droplets. Since the wrap slopes towards the centre, so do the water drops which then collect in the cup. This water is pure because only water can evaporate and not salt, which is then left behind in the bowl.

Let’s Find Out

How is desalination useful?

The process of removing salt from saline water to make it suitable for human consumption or agriculture is called desalination. As the world’s population continues to grow, there is a need to find alteranate sources of drinking water since fresh water resources are limited. Scientists are tapping the sun’s energy and creating largescale structures similar to our experiment to get drinking water from the oceans, which make up more than 70 percent of the surface of Earth. If fresh water contains 1000 ppm (parts per million) of dissolved salts, ocean water contains about 35,000 ppm of dissolved salts.

How To Make An Easy RotoCopter

SLIPPERY CARDBOARD

Stuff

A coffee mug
A small piece of cardboard
A rubber ball

1. Place the coffee mug on the table and cover it with the piece of cardboard and place the ball on it.

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2. Slowly pull the sheet and observe what happens.

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3. Now, again put the sheet back in place with the ball on it.

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4. This time flick the sheet with your index finger very quickly. Observe what happens.

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See

When you slowly pull the sheet, the ball doesn’t fall off. When you flick the sheet with your finger, the sheet flies off but the ball doesn’t. It falls into the coffee mug.

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Think about

Why does the ball fall into the glass when you flick the sheet off the glass?

Newton’s First Law of Motion states that a body at rest stays at rest and a body in motion stays in motion unless acted upon by an outside force. When you are in a moving car you are going at the same speed as the car. When brakes are applied, the brakes stop the car but not you. You move forward till your seat belt stops you. Here, when the paper sheet is slowly moved, the ball moves along with it because of friction between ball and sheet. Friction is the force between one surface and another. The friction between the ball and sheet causes the ball to move along with the sheet. When the sheet is flicked away quickly with your index finger, the ball does not move along with the sheet as the speed of the applied force is more than the friction between ball and sheet. The force of gravity on the ball makes it fall into the glass.

Winter Animals Winter Sleep

Trees shed their leaves. People wear jumpers and parkas and at home turn the heater on. But what about the animals? How can they survive low temperatures, long chilly nights and the lack of food?

Animals have developed few strategies to get through winter. They migrate to warmer places, they adapt to the season or they fall asleep and remain inactive until external conditions suit them better. This long, very deep sleep over winter time is called hibernation.

The coolest winter hibernators on Earth are:

Alpine Marmots

(Marmota marmota) are quite sleepy animals. Found in the mountain areas of central and south Europe, they hibernate for up to 8 months.

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Bats

They might be the sleepiest animal on Earth. In captivity scientists have recorded a big brown bat that spent 344 days sleeping away!

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Common Poorwill (Phalaenoptilus nuttallii)

It is the only known bird species to hibernate. This bird sleeps for up to 5 months.

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Bears

They are not always found in hibernation, except for 4 species: American Black Bear, Asiatic Black bear, Brown bear and Polar bear. Then their sleep is not a real deep one. They can wake up at any moment. So beware!

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Bumblebees

They die at low temperatures but the queen bumblebee hibernates in a hole in the ground for 6 to 8 months. As soon as weather conditions warm up the queen wakes up and works to create a brand new swarm.

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Common Box Turtle (Terrapene carolina)

They can hibernate from 80 to 160 days. This length varies according to location and turtle subspecies. These turtles are very delicate. If they get up too early, they may not survive to winter.

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Snails

They can hibernate for years. They just need to lock them inside their shell and wait for the right time to get up and go out.

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Garter snakes are social. They hibernate in groups for warmth and as soon spring arrives and temperature goes up, they, in group, go out of their winter homes. People who see them say it’s quite amazing.

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Hedgehogs can sleep through the whole winter in their in their burrows.

Albert Camus (1913 – 1960) French Nobel Prize winning author, journalist, and philosopher told us why: “In the depth of winter, I finally learned that there was in me an invincible summer.”

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Make A Sundial

DISAPPEARING COLOURS

MAKE A PARACHUTE

HOW TO DRINK SALTY WATER

How To Make An Easy RotoCopter

SLIPPERY CARDBOARD

Winter Animals Winter Sleep

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