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

Which is heavier?

Can you correctly assess the weight difference between objects of different sizes?

Hold the two metal balls in your hands to determine which one feels heavier.

The balls you were holding are exactly the same weigh, but the smaller one feels heavier.

Our assumption is in conflict with reality; the smaller of two objects that actually weigh the same feels heavier. Everyday experience tells us that larger objects will be heavier and, therefore, we expect to need more muscle strength to lift those objects. This is what is known as a cognitive illusion.

Imagine that you work in an airport and are lifting suitcases onto a conveyor belt. What would it feel like if the largest suitcase were empty? What if the smallest and most delicate suitcase contained lead? Unusually heavy luggage is marked in order to avoid unfortunate surprises and accidents.

Fakir bed

Do you dare to lie on a bed of sharp nails?

Use the handle to raise the nails of the Fakir bed and touch their tips with your fingers. Lower the nails and lie down flat on the bed. Now lift the nails up once again. Keep your head on the pillow.

It is unlikely that you even felt the nails, much less their sharpness.

There are many nails in our bed, altogether 2,335 to be exact. The pressure exerted by the nails is distributed evenly over the entire body, thus ensuring that the pressure of any single nail is minimal. The pressure is approximately the same as that which is applied to the soles of your feet when you stand barefoot on an even platform. If, therefore, you are able to stand barefoot on the floor, you will have no problem lying on the Fakir bed either. You should also note that the soles of your feet have a much higher density of nerve cells that react to pressure than exist in your back. Thus, the feeling of pressure is less on your back.

The pressure that any single object exerts on the ground depends upon the weight of the object and the area of the part that touches the ground. Therefore, a person walking in high-heeled shoes could damage a floor much more than an elephant would. Despite the enormous weight of the elephant, the pressure exerted on the floor beneath the stiletto heel of a pump can actually be significantly greater than that of an elephant’s wide foot.

Links

Cat Matikainen

The floating ball

What keeps the ball in the air?

Hold the ball in the air current and let go of it.

The ball floats in the air current while swaying only slightly back and forth.

In accordance with Bernoulli’s principle, the sum of the dynamic and static pressures of a flowing gas is constant. The greater the speed of the flow, the more dynamic pressure there is at work in the direction of the current and the less static pressure there is sideways. The dynamic pressure of the air current is always larger than that of the surrounding stationary air, and, correspondingly, the static pressure is smaller than that of the surrounding stationary air. In an air current that blows directly upwards, a ball will rise to the height at which the buoyancy created by the dynamic pressure and the weight of the ball are equal. The ball will remain in the air current, because the greater static pressure of the stationary air outside of the current pushes the ball back as it tries to escape the current. A situation in which the air current blows at an angle is more complicated. The fact that the ball does not fall is due to the combined effect of the dynamic and static pressures. The counter force exerted by the ball on the air also makes the air current turn slightly downwards.

Large birds, such as cranes, are especially talented in utilising the dynamic and static pressures of rising air currents to gain height in flight. They do not actually need to do anything other than hold out their wings. The dynamic pressure of the current lifts the birds up and the static pressure holds them automatically circling inside the current.

Links

Slow motion

Car lift

Can you lift up a small car?

Pull on the rope and watch what happens to the car.

When you pull on the rope, you are able to easily lift the car into the air.

The Golden Rule of Mechanics states that “whatever you lose in distance, you gain in power.” We can use a block and tackle to illustrate this principle. Using a rope and a stationary pulley attached to an overhead beam, we can turn the downward pull on the rope into the necessary force to lift a car. The force is increased manifold when we introduce several mobile pulleys to the equation.
Each mobile pulley in Heureka’s tackle is attached to the stationary pulley that is attached to the beam. Using this system, each mobile pulley doubles the actual pulling force. Therefore, the lifting force is 26 = 64 times as great as the pulling force.
The distances that the ropes travel will be in the same proportion to one another, but reversed. So, in order to lift the car 10 cm, the rope must be pulled about 6 metres.

Simple pulleys have been used since before the common era. It has been said that Archimedes used a block and tackle to lift ships onto docks. He is believed to have said, “Give me a lever long enough and a fulcrum on which to place it, and I shall move the world”; this statement is a fine illustration of the Golden Rule of Mechanics. In theory, it is possible to use this principle to achieve a limitless amount of force, but the practical realities, such as friction or material durability will cause problems long before such possibilities could be tested.

Links

Cat Matikainen

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