Archives September 2012

  • A file card
  • A felt tip pen
  • A long pin
  On a file draw four thick black lines as in the illustration. On the card's centre pierce a long pin. Now hold the pin head beneath the card, and spin it fast by waving it with the other hand. What do you see? HOW DOES IT WORK? What will be seen are two concentric black circles! And not many make a correct guess. It is the same explanation as for "The Moving Circle" (refer to the contents). Once the card rotates, there is a spot on each line which travels a shorter length, in comparison to other spots on the line. You will view the four spots a mite longer. And they form circles.

  • A ten rupee note
  • Two paper clips
  • Two thin rubber bends
  This is a common trick with ten rupee note folded as shown and with two paper clips on it. If you pull the bill apart holding the ends until it is flat, the two clips jump on the bill. Put two thin elastic bands around the note, inside each fold as in the illustration. Now pull the ten rupee note flat. You will be taken aback by what happens! What happens is a chain, with clips in the middle and a rubber band at either end.   HOW DOES IT WORK? You need to pull the bill ever so slowly at the ends to find out how it works. The clips and the rubber bands are positioned such that they interlink to create the chain.  

  • A ring
  • A string
  Many decades ago, novelty stores sold this item as a gimmick. But you can make it at home simply by tying a small weight, such as a ring to one end of a piece of string. Call a friend over and tell her that should she hold the free end of the string, and suspend the ring over a man's hand, it will begin to swing back and forth in a straight line like a pendulum. Again should she hold it over the hand of a woman, it begins to swing in an ellipse.   This is an instance of how a belief unwittingly influences our hand. Should you find a person for whom the gender indicator works well, you could try this. Let the person hold the indicator so the ring is suspended inside a drinking glass. Just tell him more...

  • A sheet of typewriter paper
  • Scissors
Cut a one inch (2.5 cm) strip from the side of a typewriter paper. Study Figure 2 and tie an overhand knot in the centre of the strip. Pull the knotted strip taut and then flatten it.   As in Figure 2, fold end A over the knot. If you hold the knot up to a light what you will notice is a perfect five-pointed star in a regular pentagon. There are many amazing mathematical properties in it.  

  • A chessboard
  • Some grains of rice
  • A compass
  • A sheet of plain paper
  • Some coloured pens
If on a chess board one continues placing double the number of grains of rice, as compared to the previous one, on every square, i.e., one grain on the first square, two grains on the second square, four grains on the third square and sixteen on the fourth square and likewise. Calculate the number of grains of rice there will there be on the tenth square and the total grains on the board. Draw a circle with a radius of 2 inches with a compass. Draw another circle by placing the point of the compass on one edge of the first circle. Place the point of the compass at the points where the second circle intersects the first circle- Continue drawing circles from every intersection until there are no more. To form a proper hexagon more...

There is no mathematical problem that better Illustrates how a flash of intuition and an aha! — will provide a quick proof. Look at the illustration. The area of the larger square is exactly twice of the smaller square one in Figure 1, Is it correct? HOW DOES IT WORK? It is not necessary to make tedious calculations. Just rotate the inner square in your mind to the position shown in Figure 2, and you will see at once that the inner square is exactly half the area of the outer square.- Mathematicians call this a "look-see" proof.

  • A small coin
  Turn your back and ask a friend to hold a One rupee coin inside the fist of any of his hands. Ask him to hold up the hand with the coin high above his head, even as he counts to 50. Now ask him to lower the arm and turn around. Now ask the friend to extend both his hands where the back of the hands are up. Try and guess which fist hides the coin. You can guess correctly every time. HOW DOES IT WORK? Gravity makes the blood in the veins of the hand that is raised to come down. The downward motion of the blood causes the back of the hand that was held up to become a little lighter than the other one.

  • A pencil or a pen
  • Paper
  Try to write your name on the paper while making a circular motion with one foot. You will not be able to do it.   HOW  DOES  IT  WORK?   The brain which sends messages to the entire body will be unable to direct your foot to go around in circles while telling your hand to write.

  • A handkerchief
  A bit of secrecy is involved in this one. Tie a few tight knots in a handkerchief and secretly place it under one of your armpits. It will remain concealed by your clothes. Allow a friend to feel the pulse in the arm under which the handkerchief is hidden. Ask him to count up to three and you will stop your pulse. The pulse will stop much to the surprise of your friend.   HOW  DOES  IT  WORK?   To stop your pulse, all you have to do is press the sides of your arm against the knotted cloth under the armpit. Pressure is created on the arm's main artery. This lowers the pulse rate to a level which cannot be felt. After some time snap your fingers and end the pressure. The more...

  • A jug of water
  • Glasses , cups, bowls etc. , of different sizes
  • Newspapers
  • Some white paper
  • Red and blue marking pens
  Take containers and glasses of different shapes and fill them with water. Pour all the water from each container into a measuring jug. Measure the water in the jug and divide the total quantity by the number of containers. This is how the average amount of water in each glass can be calculated. The weather column in your newspaper shows the daily maximum and minimum temperature. Make a note of the temperature for a period of fifteen days. On the blank sheet of paper, draw the axes of a graph. Make 15 divisions on the horizontal axis and label these as days. Divide the vertical axis into 5 degree units. Begin with the maximum temperature for each day. Mark the temperature on the more...


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