A cat on a mat

By Upali Salpadoru
If a cat sits on a mat and when you pull the mat, will the cat come? You don’t need a cat and a mat to find this out. We could substitute a coin for a cat and a strip of paper for a mat.
The coin is on a strip of paper, standing on its edge. The paper is jutting over the table. Now, take a ruler and hit the paper so that it gets pulled out quickly.
Does the coin come?
Further activities:
The experiment may be repeated in many other ways. Here are some suggestions.
• Use the same coin and paper but, vary the force.
• Use the same coin and same force but, vary the mat. [Instead of paper you may use cloth]
• Use the same paper and same force but, different coins or, other objects.

****

Bubbles go where the air goes!

Air is invisible. Yet, we feel the air, when it blows or when it comes from a revolving fan. How do we check the movement of an invisible substance? The experimental method is to use tracers. A tracer is a substance that can be seen or detected by a sensor.
When the branches sway and the leaves fly, we conclude that the air is moving. When there is smouldering (Often producing smoke) the smoke particles will go where the air goes. When the particles of air or, a gas or, a liquid, moves in a particular direction, we call it a ‘current’; air currents or water currents. The observatory learns about the movement of air in the upper atmosphere, by sending up Hydrogen filled balloons. Transmitters called ‘Radiosonde’, are attached to these balloons, which send signals indicating where the wind is blowing...
Our experiment is to find out how the air moves around a hot body such as a candle flame or, an electric iron.
Fig 1. Nellie blowing bubbles into the magic box.
Take an empty cardboard box. Open the lid and place a board of non inflammable material at the bottom. Cut a window on one side and paste cellophane paper over the opening, so that you could see inside. Keep an electric iron or, a burning oil lamp, on the non combustible surface. [If you cannot find a non combustible substance, you may add a layer of sand].
Close the lid, keeping the end of the power cord out. Make two openings at the top, and fix two pieces of thick paper rolled up as cylinders. They are shown in the diagram as ‘A’ and ‘B’.
Switch on the iron. If it is a lamp or a candle, light it carefully. Close the lid and place the two chimneys A and B. Blow soap bubbles near the box and observe.
You may even use smoke from a joss stick, instead of soap bubbles.
Warning
If you are using an oil lamp or a candle, you must have a bucket of water, ready to extinguish the fire if the box catches fire.
This kind of particle movement in a gas or a liquid carrying heat energy, is called a convection current.

****