204 Simple Science Experiments ~ {ERG} - Page 6

LoneRanger · #76 06-19-2008, 12:02 PM

64. Shooting Backwards

Hold an empty bottle horizontal and place a small paper ball just inside its neck. Try to blow the ball into the bottle. You cannot! Instead of going into the bottle, the ball flies towards your face.

When you blow, the air pressure in the bottle is increased, and at the same time there is a partial vacuum just inside the neck. The pressures become equalised so that the ball is driven out as
from an airgun.

LoneRanger · #77 06-20-2008, 01:12 PM

65. Blowing trick

Place a playing card on a wineglass so that at the side only a small gap remains. Lay a large coin (half a dollar or 10 new pence) on the card. The task is to get the coin into the glass. Anybody who does not know the trick will try to blow the coin into the gap from the side without success.

The experiment only works if you blow once quickly into the mouth of the glass. The air is trapped inside and compressed. The increased pressure lifts the card and the coin slides over it and into the glass.

LoneRanger · #78 06-21-2008, 11:40 AM

66. Compressed air rocket

Bore a hole through the cap of a plastic bottle, push a plastic drinking straw through it and seal the joints with adhesive. This is the launching pad. Make the rocket from a four-inch-long straw, which must slide smoothly over the plastic straw. Stick colored paper triangles for the tail unit at one end of the straw, and at the other end plasticine as the head. Now push the plastic tube into the rocket until its tip sticks lightly into the plasticine. If you press hard on the bottle the projectile will fly a distance of 10 yards or more.

When you press the plastic bottle, the air inside is compressed. When the pressure is great enough, the plastic straw is released from the plug of plasticine, the released air expands again, and shoots off the projectile. The plasticine has the same function as the discharge mechanism in an airgun.

LoneRanger · #79 06-22-2008, 03:59 PM

67. Egg Blowing

Place two porcelain egg-cups one in front of the other, with an egg in the front one. Blow hard from above on to the edge of the filled cup. Suddenly the egg rises, turns upside down and falls into the empty cup. Because the egg shell is rough, it does not lie flat against the smooth wall of the egg-cup. Air is blown through the gap into the space under the egg, where it becomes compressed. When the pressure of the cushion is great enough,
it lifts the egg upwards.

LoneRanger · #80 06-23-2008, 07:11 PM

68. Curious air currents

If you stand behind a tree trunk or a round pillar on a windy day, you will notice that if offers no protection, and a lighted match will be extinguished. A small experiment at home will confirm this: blow hard against a bottle which has a burning candle standing behind it, and the flame goes out at once. The air current divides on hitting the bottle, clings to the sides, and joins up again behind the bottle with its strength hardly
reduced. It forms an eddy which hits the flame. You can put out a lighted candle placed behind two bottles in this way, if you have a good blow.

LoneRanger · #81 06-24-2008, 12:38 PM

69. Bernoulli was right

Lay a postcard bent length ways on the table. You would certainly think that it would be easy to overturn the card if you blew hard underneath it. Try it! However hard you blow, the card will not rise from the table. On the contrary, it clings more firmly.

Daniel Bernoulli, a Swiss scientist of the eighteenth century, discovered that the pressure of a gas is lower at higher speed. The air stream produces a lower pressure under the card, so that the normal air pressure above presses the card on to the table.

LoneRanger · #82 06-25-2008, 01:09 PM

70. Wind-proof coin

Push three pins into the middle of a piece of wood and lay a coin (5 new pence or 25-cents) on top of them.

You can make a bet! Nobody who does not know the experiment will be able to blow the coin off the tripod.

The metal cannot hold the gust of air on its narrow, smooth edges. The gust shoots through under the coin and reduces the air pressure, forcing the coin more firmly on to the pins. But if you lay your chin on the wood just in front of the coin and blow with your lower lip pushed forward, the air hits the underside of the coin directly and lifts it off.

LoneRanger · #83 06-26-2008, 11:46 AM

71. Trapped Ball

Place a table tennis ball in a funnel, hold it with the mouth sloping upwards, and blow as hard as you can through the spout. You would hardly believe it, but nobody can manage to blow the ball out.

The air current does not hit the ball, as one would assume, with its full force. It separates and pushes through the places where the ball rests on the funnel. At these points the air pressure is lowered according to Bernoulli’s law, and the external air pressure pushes the ball firmly into the mouth of the funnel.

LoneRanger · #84 06-27-2008, 01:39 PM

72. Flying coin

Lay a sixpence or a dime four inches from the edge of the table and place a shallow dish eight: inches beyond it. How can you blow the coin into the dish!

You will never do it if you blow at the coin from the front - on the false assumption that the air will be blown under the coin because of the unevenness of the table and lift it up. It will only be transferred to the dish if you blow once sharply about two inches horizontally above it. The air pressure above the coin is reduced, the surrounding air, which is at normal pressure, flows in from all directions and lifts the coin. It goes into the air current and spins into the dish.

LoneRanger · #85 06-28-2008, 12:02 PM

73. Floating card

Many physical experiments seem like magic, but there are logical explanations and laws for all the strange occurrences. Stick a thumbtack through the middle of a halved postcard. Hold it under a cotton spool so that the pin projects into the hole and blow hard down the hole. If you manage to loosen the card, you really expect into fall. In fact, it remains hovering under the spool.

Bernoulli’s law explains this surprising result. The air current goes through at high speed between the card and the spool, producing a lower pressure, and the normal air pressure pushes the card from below against the spool. The ascent of an aircraft takes place in a similar manner. The air flows over the arched upper surface of the wings faster than over the flat under-surface, and therefore the air pressure above the wings is reduced, providing lift.

LoneRanger · #86 06-29-2008, 02:19 PM

74. Wind Funnel

Light a candle and blow at it hard through a funnel held with its mouth a little way from the flame. You cannot blow out the flame; on the contrary it moves towards the funnel.

When you blow through the funnel the air pressure inside is reduced, and so the air outside enters the space through the mouth. The blow air sweeps along the funnel walls: if you hold the funnel with the edge directly in front of the flame, it goes out. If you blow the candle through the mouth of the funnel, the air is compressed in the narrow spout, and extinguishes the flame immediately on exit.

LoneRanger · #87 06-30-2008, 03:21 PM

75. Explosion in a bottle

Throw a burning piece of paper into an empty milk bottle and stretch a piece of balloon rubber firmly over the mouth.

After a few moments, the rubber is sucked into the neck of the bottle and the flame goes out.

During combustion, part of the expanded, hot air escapes. After the flame goes out the diluted gas in the bottle cools and is compressed by the external pressure. The rubber is therefore stretched so much that the final pressure equalization only occurs
if you break the bubble, causing a loud pop.

LoneRanger · #88 07-01-2008, 06:44 PM

76. Twin tumblers

Light a candle stump in an empty tumbler, lay a sheet of damp blotting paper over the top and invert a second tumbler of the same size over it. After several seconds the flame goes out and the tumblers stick together.

During combustion the oxygen in both tumblers is used up - the blotting paper is permeable to air. Therefore the pressure inside is reduced and the air pressure outside pushes the tumblers together.

LoneRanger · #89 07-02-2008, 12:58 PM

77. Coin in the well

Place a coin in a dish of water. How can you get it out, without putting your hand in the water or pouring the water from the dish?

Put a burning piece of paper in a tumbler and invert it on the dish next to the coin. The water rises into the tumbler and releases the coin.

During combustion the carbon contained in the paper, together with other substances, combines with the oxygen in the air to form carbon dioxide. The gas pressure in the tumbler is reduced by the expansion of the gases on heating and contraction on cooling. The air flowing in from outside pushes the water into the tumbler.

LoneRanger · #90 07-03-2008, 01:51 PM

78. Bottle ghost

An empty wine bottle, which has been stored in a cool place, has a ghost in it!

Moisten the rim of the mouth with water and cover it with a coin. Place your hands on the bottle. Suddenly the coin will move as if by a ghostly hand.

The cold air in the bottle is warmed by your hands and expands, but is prevented from escaping by the water between the bottle rim and the coin. However, when the pressure is great enough, the coin behaves like a valve, lifting up and allowing the warm air to escape.