# Archives September 2012

#### A VIBRATING CARD

YOU NEED:
• A saw
• A playing card
The sound of a reed instrument like a clarinet or a saxophone, is the result of the vibration of a reed. Vibration of the air creates sound in wind instrument like violins, comets and trombones. Again in musical instruments like violins or cellos the sound is created because of friction between the bow and the string. The pitch of the sound depends on how fast the vibration is .  This is amply demonstrated if the edge of a playing card is rubbed against the teeth of a saw. If you rub the card slowly it produces sound at a lower pitch which increases in crescendo when the card is moved faster. HOW DOES IT WORK? There is no difference between the manner in which vibrations are created when a card is rubbed against the cutting edge more...

#### THE DISTORTED PICTURE

Has this ever happened to you that you were watching a cricket match on the televison and you let out a cheer when a player hit the ball over the fence. Try it. Stand as far away from the television set as possible, then cheer as loudly a possible. You will notice that, when you do this the sound distorts the picture on the screen. It seems as if the vertical hold in the television is malfunctioning.   HOW DOES IT WORK? Surprisingly the cheer you let out has no effect on the television screen whatsoever. The strong vibration of the sound you have just made rattles your eye and it creates a strobe effect influencing your vision of the television screen’s scanning beam. This is what creates the blurring effect.

#### THE DISAPPEARING COIN

YOU NEED:
• A glass of water
• A small coin
• A table
Do you know that you are capable of making a coin simply disappear. Fill a clear glass, with straight sides, with water. Put it on the table and then place a coin about six inches (15cms) behind it. Once viewed through the glass, one will see two coins lying side by side. Now close one of your eyes- Lo! One coin will vanish! HOW DOES IT WORK? Light passing through a glass of water causes refraction" which means its path is bent. This causes objects to appear to be in a different position than in reality. In this experiment for instance, one eye sees the coin directly, while the other gets to see the refracted image of the coin which seems to be in a different position. The effect is that you more...

YOU NEED:
• A soft pencil
• A sheet of paper
• A piece of tape
• A glass of water
Firstly rub a soft pencil point back and forth to create a black area of graphite. Rub your thumb over the spot so that you have graphite on your thumb. Now press the tip of your thumb against the sticky side of the cellophane tape. Hold the tape up to the light to see a clear thumb print. Secondly put a full glass of water on a table. When the water settles down, press a thumb firmly against the side of the glass which is nearer to you. Now bend your head till you can view the tip of the thumb through the water. The ridges of the thumb will be clearly visible. HOW DOES IT WORK? A thumb print comprises of tiny ridges. The cellophane tape more...

#### THE MOVING CIRCLE

YOU NEED:
• White cardboard
• Scissors
• A sharpened pencil stub
• Felt – tip – pen
Cut a circle about six inches (15 cm) in diameter from a piece of white cardboard. Make a hole in the middle and push a sharpened pencil stub through it to make a top. Take the felt – tip pen, and draw a black circle on the disk as in the illustration. Guess what you will see you spin the top? You will see small concentric circles and that too, two of them!   HOW DOES IT WORK? The illustration reveals that XY drawn the diameter through the middle of the small circle, will intersect it at pots. As the disk spins, the spots move in almost a straight line compared to other spots along the little circle. The eyes see them for a longer time so as to more...

#### DOUBLE THE DISTANCE

YOU NEED:
• Two mirrors
• A tomato or any other object
Place two mirrors on a table face to face situated one foot (30cm) apart. Place a tomato halfway among the mirrors. The tomato's images form endless reflections in the mirrors. The question is: If you bring the tomato closer to one of the mirrors, will the two closest images come nearer, further away, or remain in the same place? Try to figure out the answer to this. HOW DOES IT WORK?    It does not matter where the apple is placed between two mirrors, the two closest images will have be two feet apart- For instance, if the apple is moved to a position which is one inch (2.5 cm) from one mirror, its image in that mirror will be two inches (5 cm) from the apple. Its image in the more...

#### A SIMPLE THERMOMETER

YOU NEED:
• A small drill
• A bottle
• Water colour
• Some ice
Insert a tube through a small hole drilled through cork. Fill a bottle with coloured water. Cap the bottle with the cork. Seal the joints with adhesive to make water tight. The rise in water level in the tube is measure of temperature. Stand the bottle in icy water mark the level of water in the tube as 0 degree. Make markings of other temperatures by comparing with a doctor's thermometer. Place the entire apparatus in the sun for a few hours. Check the water level in the tube, it would have risen. HOW DOES IT WORK? As the colured water in the bottle heats up, it expands and flows upwards into the glass tube. This process gets reversed as the water cools. Mercury thermometers work in the same manner.

#### BOUNCING BACK

YOU NEED:
• A bouncing ball made of hard rubber
• A table
Here is a trick to amuse your friends. You can tell them you have discovered a way by which you can throw the ball in such a way that it will halt in midair, turn directions, and come to you. Your friends would like to see this trick. It is not difficult to procure a bouncing ball made of hard rubber. You can get it a shop selling sports goods or even at your neighborhood store. A little spin on such a ball makes it bounce. Now try this on table  that is standing on a hard surface. Throw the ball as  shown in the ''illustration by the arrow marks. The ball will hit the table's underside; reverse its direction and bounce back to you.     HOW DOES IT WORK? As more...

#### MERGING WEIGHT AND FRICTION

YOU NEED:
• Two cardboard rolls from a paper towel roll
• A ruler
Arrange the two cardboard rolls side by side and ,balance the ruler on top of the two as shown in the illustration. If you happen to rotate the rolls inward, as indicated the arrows, the ruler remains balanced. It may shift back and forth slightly but it remains balanced. Even though it may move backwards and forwards.  It however remains balanced. Rotate the cardboard rolls in the opposite direction. The ruler will slowly travel to one side till it falls off the rolls.                    HOW DOES IT WORK?        The action that you have just noticed is the result of merger of weight and friction. Take the case of the rolls rotating inwards. The moment the ruler moves a little bit to the left — its weight on the cardboard roll increases. This more...

#### IMMOBILE BOLTS

YOU NEED:
• Two bolts
This one  does not need any apparatus. This experiment  can be done in the head. Just imagine that  bolts are placed together so that their three dimensional spiral structures, called a helix, intermesh with, each other as shown in the illustration. Now move the bolts around each other in your mind. It will be similar to twiddling your thumbs holding each  head so as not rotate it. Move the bolts in the direction of the arrow. Will the heads i)                    Come close to each other ii)                   Move away from each other iii)                 Or be static? Solution : You will be surprised to learn that the answer is iii) .It is comparable to a situation where someone is  up an escalator moving downwards.

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