Too much air

Are ships sinking in the Bermuda Triangle?

Press the button to send air bubbles into the plastic tube and watch what happens to the ship.

When the bubbles reach the surface of the water, the ship begins to sink.

Gas released from the bottom rises as bubbles toward the surface. A large amount of bubbles decreases the mean density of the water, and a ship situated where the gas reaches the surface will lose the buoyant force of the water and sink like a stone.

The Bermuda Triangle is a triangular region in the Atlantic Ocean, located between the southern tip of Florida, and the isles of Puerto Rico and Bermuda, where numerous ships and aeroplanes have allegedly disappeared. According to one theory, the reason for the disappearances of ships is the methane gas in the sea bottom around Bermuda. There is, however no theoretical or statistical evidence for this hypothesis.

 

Links

Funny but rather noisy about Acrhinmedes principle

Slow bubbles

Which bubble will rise the fastest?

Pump bubbles into the tube and watch them rise.

The larger bubbles rise faster than the smaller bubbles.

The pressure in the liquid increases as you go deeper. The difference in the pressures on the upper and lower surface of an object in liquid creates the buoyancy of the object. In this example, the bubble is the object. Buoyancy lifts the bubble to the surface, because air is lighter than liquid.
The liquid resists the movement of the objects within it. This phenomenon is known as fluid resistance. The degree of the fluid resistance depends upon, for example, the speed and cross-sectional area of the object, and the viscosity of the liquid. The viscosity of the silicon oil in the tube is high. Therefore, the bubbles rise slowly. The larger bubbles rise faster than the smaller bubbles, because the buoyancy of the bubble is proportional to the size of the bubble, and the fluid resistance is proportional to its cross-sectional area. When the size of the bubble increases, the volume increases relatively more than the cross-sectional area.
In silicon, the bubbles rapidly reach their terminal velocity. Once this occurs, all bubbles of the same size will rise at an equal rate. If a large bubble catches up to and “swallows” a smaller bubble, the resulting larger bubble will again for a moment accelerate in speed.

The word viscosity derives from “viscum album”, the Latin name for mistletoe. People used to smear tree branches with the thick, gluey resin from mistletoe berries in order to catch birds when they land.

Flying carpet

Low-flying carpet

Use the hose to fill the compressed-air tank. Release the hose by pressing the button and push yourself off to slide.

The carpet remains in the air for about 30 seconds, as it ‘flies’. In the end, the air in the tank runs out, the air stream weakens, the pressure under the carpet decreases and the carpet lowers to the ground.

The air leaks through the small holes in the bottom of the tank, thereby forcing the carpet upwards. The 'skirt' around the carpet prevents the leaking air from immediately escaping from under the carpet. The resulting extra pressure keeps the carpet hovering above the ground. The carpet settles at the height in which the combined lifting force of the air stream and the pressure of the air underneath the carpet are equal to the weight of the carpet with its passengers. When the carpet is off the floor, it moves nearly without friction, so it only requires the force to overcome inertia to start it off – or to stop it.

The same principle is applied to a hovercraft, which is an extremely handy means of transportation in the Finnish archipelago during the period when the sea is thawing out in spring. Hovercrafts can be used to move about on land, water and ice. The first hovercraft was designed in Sweden at the beginning of the 18th century. It was, however, never built. It is not likely that it would have worked, since it was designed to use high pressure air created by human power. As far as is known, the first functional hovercraft was built by the Finnish Engineer Toivo Kaario in 1935.

Links

Cat Matikainen
Flying carpet