# Archives August 2012

#### THE STICKING FINGER

YOU NEED
• A ruler
It is well known fact that if you rest a ruler one on each end of your extended forefingers, and if you move them towards each other they will perforce meet at the centre of the ruler. The explanation is simple. Should one finger travel ahead of the other, the weight on that particular finger increases. Therefore, it raises the friction between the ruler and the finger. This in turn lowers the friction on the other finger allowing it to travel ahead. Now the question is: In a situation where both fingers are at the centre of the ruler, what is likely to happen should you move them back to the ends of the ruler. Trying guessing the answer before you  try the experiment. You are likely to be surprised.  HOW DOES IT WORK?  When one finger begins to move, its friction more...

#### A MYSTERIOUS PROPELLOR

YOU NEED:
• Two pencils
• A file and a pin
• A rectangular piece of cardboard
Cut notches along the edge of a pencil. Stick a pin through the centre of the cardboard and attach it to the pencil's  eraser as in the top illustration. The hole in the "propeller"' must be a bit larger than the pin, in order to cut down on friction. In your left hand, hold the end of the pencil. With your right hand, rub the second pencil back and forth across the notches as in the second illustration. If the tip of your first finger slides along the right side of the notches, the cardboard "propeller" will rotate rapidly  towards the left. If the pencil being rubbed is moved a trifle forward so that the tip of your thumb now slides along the left side of the notches, the "propeller" will stop and start turning towards the right! The more...

#### STICKY INERTIA

YOU NEED:
• A matchbox
• A paper match
• A cylindrical cork
Three impossible feats can be pulled off if you can be a little sneaky. It is fun and a great source of entertainment for your friends. Consider these three feats: Drop a matchbox from a height of six inches (15 centimeters) over a table top so that it lands on its end and remains upright. 2.   Drop a paper match so that it lands and stays on its edge. 3.    Drop a cylindrical cork so that lands on one end. The way to go about it: For1: Push the matchbox drawer about an inch upward holding the box vertically. You can conceal the protruding top with your hand. When you drop it over the table top, the match box will not bounce.   HOW DOES IT WORK?   For 1:     Once the matchbox hits the table more...

#### A JUMPING PEN

YOU NEED:
• A pencil
• A square of paper 6” x 6”
• A tape & rubber band
• A ball point pen with cap (as the illustration)
A pen can be made to jump back into its cap as though pulled by a invisible hand, a magnet or a rubber band. Take the pencil and roll a square of paper around it like a tube about six inches (15cm) long. Tape it. Now tape the end of a rubber band to one end of the empty tube, as shown in the illustration and then push the rubber band into a tube. Procure a ballpoint pen with a cap shaped as in the illustration. Point first Insert the pen into the tube. Go through the motion of trying to hook its pointed end on the rubber band. Take  the pen some way out of the tube. It zooms back into the tube as if jerked by more...

#### THE TRICKY DICE

YOU NEED:
• Two dice
• A glass
This is  one experiment that you can baffle your friends with. Take the two dice and hold it against the side of the glass as in the illustration. The tricky part is to throw the dice into the air, one at a time and ensure that it drops in to the glass. It is easy to toss and drop the first dice in the glass. But if the same thing is  tried with the second dice, the first one tends to fly out of the glass. Allow your friends to try and do it. They won't be able to do it either. Here is how you can catch both the dice in the glass.   HOW DOES IT WORK? The secret is not to toss the second dice. The idea is to let the dice drop and then lower the glass fast more...

#### THIS RIGID NEWSPAPER

YOU NEED :
• A sheet of newspaper
Hold a sheet of newspaper in your left hand and let the sheet hang down as shown in the illustration. Now can you poke your index finger through the paper? While it seems unlikely, it can be done. Jab your finger as rapidly as you can at the centre of the paper. You need to be fast and then only will your finger go through the sheet    HOW DOES IT WORK?  When you jab your finger into the newspaper the air pressure behind the newspaper maintains a rigidity in the paper which is also reinforced by the newspapers inertia, this is what causes it to tear.

#### SIMPLE ROTATION

YOU NEED:
• Two kitchen towel rolls
• A large cylindrical can
Gingerly place one toilet paper roll on top of the other as shown in the top illustration. Rotate the top roll with your fingers along the table top.  As you would expect, the bottom roll rotates in the opposite direction and the two rolls travel together merrily. This  time around change the top roll with a cylindrical can as in the illustration. Should you rotate the can, do you think the cardboard tube will move smoothly with the can or will it travel faster or slower than the can? The surprising thing is that the two companions travel as  if they were sized buddies.   HOW DOES IT WORK? Simply the point of contact between the can and the tube travel on the same speed and cover the same distance. This has nothing to do with the sizes more...

#### THE ROTATING RING

YOU NEED: • A ring and some string       When an ice skater spins with outstretched arms, then quickly lowers her arms, her speed of rotation increases enormously. This is because her arms are suddenly forced to move in a smaller circular path. This effect can be demonstrated with a finger ring and a piece of string. Attach the string to the ring so that it hangs down, as in the illustration, while you hold the ends of the string. Now twirl the ring in a circle about six inches (15 cm) in diameter. As you twirl the ring, pull on the ends of the string. The ring speeds up.   HOW DOES IT WORK?   When the ends of the strings are pulled, the ring is forced to go around in a smaller circle, causing its angular velocity to increase suddenly. Much the same thing happens when water goes down more...

#### MOTION IN SURFACE TENSION

YOU NEED :
• A piece of thick plastic
• A tub
• Some water
• Some liquid detergent
Cut out of plastic in the shape of a boat bottom, having one side pointed and the other straight. In the centre of the straight side cut a small ‘V’ shaped notch. Place this shape in a tub of water. The shape will not move once the water is still. Without shaking the water, carefully  put a drop of detergent in the 'V’ shaped notch that you had cut earlier. You will see that the piece of plastic begins to move.   HOW DOES IT WORK? This  happens because the detergent disturbs the surface tension of the water and the plastic moves Forward.

#### HOW PENDULUMS WORK

YOU NEED :
• Cardboard tube
• An apple
• A rubber bail
• An Iron nut
Do you know that the time taken for a pendulum to swing is not related to the weight attached to it but to the length of string it is attached to. You can test this by taking a number of strings of the same lengths and attaching to it different weights, then again by taking different lengths and attaching the same weight to it, and so on.   HOW DOES IT WORK? Since the pull of gravity is the same on all the objects, irrespective of their weight, all the objects swing at the same speed. This is why the weight of the object has no relation to the swing of the pendulum.

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