51. Magnetic or not?

Many iron and steel objects are magnetized without one realizing it. You can detect this magnetism with a compass.

If a rod is magnetized, it must, like the compass needle, have a north and South Pole. Since two unlike poles attract and two like poles repel, one pole of the needle will be attracted to the end of the bar and the other repelled. If the bar is not magnetized, both poles of the needle are attracted to the end.



52. Compass needle

Stroke a sewing needle with a magnet until it is magnetized and push it through a cork disk. Put the needle into a transparent plastic lid cntaining water and it turns in a north-south direction. Stick a paper compass card under the lid. The needle points towards the magnetic North pole of the earth. This lies in North Canada and is not to be confused with the geographical North Pole, round which our earth rotates. The deviation (declination) of the magnetic needle from the true north is 80 in London and 150 in New York (in a westerly direction) and l0 in Chicago and 150 in Los Angeles, (in an easterly direction).

53. Dip to the Pole

Magnetize two steel pins so that their points attract each other strongly. Push them into the ends of a piece of foam plastic about as thick as a pencil and balance this by means of a sewing needle over two tumblers (by shifting the pins and pulling off pieces of plastic), if you allow this compass to swing in a north-south direction, it will come to rest with the end facing north sloping downwards. The compass needle comes to rest parallel to the magnetic field lines, which span the earth from pole to pole. This deviation (dip) from the horizontal is 670 in London, 720 in New York. 600 in Los Angeles and at the magnetic poles of the earth 900.



54. Magnetic ducks

Make two ducks from paper doubled over and glued and push a magnetised pin into each one. Place the ducks on cork disks in a dish of water. After moving around they line up with their beaks or tail tips together in a north-south direction.

The ducks approach each other along the magnetic field lines. Their movement is caused by different forces: the attraction of unlike magnetic poles, the repelling effect of like poles, and the earth’s magnetism. Set the magnets so that two poles which will be attracted are placed in the beaks.

this all brings back old memories... nostalgia..,.,



Diving bell

You can immerse a pocket-handkerchief in water, without it getting
wet: stuff the handkerchief firmly into a tumbler and immerse it upside down in the water.

Air is certainly invisible, but it nevertheless consists of minute particles, which fill the available space.

So air is also enclosed in the upturned glass, and it stops the water entering. If, however, you push the glass deeper, you will see that some water does enter, due to the increasing water pressure, which compresses the air slightly. Diving bells and caissons, used under water, work on the same principle.

56. Balloon in the bottle


Do you believe that it is always possible to blow an ordinary balloon right up! You will be surprised: push a balloon into a bottle and stretch its mouth-piece over the opening. Blow hard into the balloon. It is only possible to stretch the rubber before your breath runs out.

As the pressure of the air in the balloon increases, so does the counter-pressure of the air enclosed in the bottle. It is soon so great that the breathing muscles in your thorax are not strong enough to overcome it.

57. Air Lock

Place a funnel with not too wide a spout into the mouth of a bottle and seal it with plasticine so that it is airtight. If you pour some water into the funnel, it will not flow into the bottle.

The air enclosed in the bottle prevents the water entering. On the other hand, the water particles at the mouth of the funnel, compressed like a skin by surface tension, do not allow any air to escape.

Close one end of a straw, push the other end through the funnel, lift your finger, and the water flows at once into the bottle. The air can now escape through the straw.



58. Hanging water

Fill a glass to overflowing with water and lay a postcard on it. Support the card with one hand, turn the glass upside down and remove your hand from the card. it remains on the glass, and allows no water to escape.

With a glass of normal height, a weight of water of about 2 ounces presses on each square inch of card. On the other hand the pressure of air from below is about one- hundred times as great on each square inch, and presses the card so firmly against the glass that no air can enter at the side and so no water can flow out



59. Weight of air on paper

Lay a cigar-box lid over the edge of a smooth table. Spread an undamaged sheet of newspaper and smooth it firmly on to the lid. Hit the projecting part of the lid hard with your fist. It breaks, without the paper flying up.

The lid is only slightly tilted when it is hit. In the space formed between the lid, newspaper and table, the air cannot flow in quickly enough, so that there is a partial vacuum, and the normal air pressure above holds the lid still as if it were in a screw clamp.



60. Bottle barometer

Stretch a piece of balloon rubber over the mouth of a milk bottle and stick a straw on top of it. As the air pressure varies daily according to the state of the weather, the end of the straw moves up and down.

When the air pressure is higher in fine weather, the rubber is pressed inwards, and the end of the pointer rises. When the air pressure falls, the pressure on the rubber is reduced, and the pointer falls.

Because the air in the bottle will expand if it is heated, the barometer should be placed in a spot where the temperature will remain constant.

61. Weather Frog

A tree frog made of paper will climb up and down a ladder like a real weather frog and predict the weather. Bend a 2f-inch-long strip of metal into a U-shape and bore through it so that a sewing needle can be turned easily when inserted through the holes. The needle is made able to grip by heating, and the frog, made from green paper, is fixed on to it by a thin wire. Stick the metal strip firmly on to the middle of the wall of a four-inch-high jar, and at the side a cardboard ladder.

Wind a thread round the needle, with a small counterweight at the end. Stick a paper disk on a piece of plastic foil, and draw the other end of the thread through the middle. The foil is stretched over the mouth of the jar so as to be smooth and airtight, the thread is tightly knotted, and the hole sealed.

When the air pressure is high (fine weather) the plastic foil is pressed inwards and the frog climbs up. When the pressure is low (bad weather) the pressure on the foil is less and the frog climbs back down.



62. Fountain

Punch two holes in the lid of a jam jar and push a plastic straw a distance of two Inches through one. Fix three more straws together with adhesive tape and push through the other hole. Seal the joints with warm plasticine. Screw the lid to the jar, which should contain some water, turn it upside down and let the short straw dip into a bottle full of water: a fountain of water rises into the upper jar until the bottle is empty.
The water pours out through the long tube, and the air pressure in the jar becomes less. The air outside tries to get in and pushes the water from the bottle.



63. Match lift

It is simple, using air, to lift matches from the table into their box. Hold the case between your lips and lower it over the matches. Draw a deep breath, and the matches hang on to the bottom of the case as though they were stuck on.

By drawing in breath you produce a dilution of the air, in the case. Air pressure pushes the matches from underneath towards the opening. Even a single match can be raised in this way, if the air is drawn in sharply.

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