Sunday, 30 January 2011

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.



Why does the series of images appear to be moving?

Spin the zoetrope and look in through the small slits. You can also design and draw your own animation and see if it works.

The pictures begin to come to life; they appear like a short film. You will also note that the zoetrope’s story is looped; it always ends in the same image from which it began.

You see a series of consecutive images divided by black framing. When the consecutive images follow each other closely, your brain perceives the images as a continuous motion, even though each image presents one individual still picture. The black surface between the slits corresponds to a film projector’s shutter; while the machinery shifts the image from one frame to the next, the shutter obscures this event. Therefore, the images flow in front of your eyes as a seemingly continuous stream.

The zoetrope was developed in 1834 by Englishman William Horner, who originally called it a Daedalum. In 1867, Frenchman Pierre Desvignes introduced it to the market with its new name, zoetrope, a wheel of life.

Film projectors present images at a speed of 24 frames per second. A long film is, in reality, truly long, approximately 2.5 kilometres of film. Within the European PAL system, a digital television image can be changed 25 times per second. The jerky effect of these changes can be reduced by changing the image in an interlocking fashion, in other words, by moving a half frame at a time. This can be accomplished at a doubled rate of 50 times per second.

Spinning head

Which way is the head spinning?

Look at the face from a distance of a few metres for a minimum of one full rotation. Also try looking at it while covering one eye, as well as changing viewing position and distance.

The head is actually spinning in the same direction all the time. However, as the convex side changes to the concave side, the direction of the spinning head appears to change.

We do not observe the world in a passive manner, but rather, our brain makes interpretations of the information sent by our senses. These interpretations also draw upon our experiences, and we try to change surprising or odd observations into something more usual. The real human faces we see are convex. As we look at the spinning head, we ignore the observational cues which tell us that the other side is concave. Instead, the direction of the spinning appears to change when light and shadow change their locations on this face that we interpret as being convex.

The illusionary effect is further affected by light and depth perception. By covering one eye, we miss the concave features of the face, since the ability to perceive depth is based on the use of both eyes. The significance of light is revealed by viewing the face from different directions.

Depth perception is the ability to perceive the world in three-dimensional form and to assess distances. Depth perception is based on slightly different superimposed images that our eyes provide of the same object. Test this principle by lining up your finger with, for example, the vertical frame of a door. Now open and close each eye.

More about optical illusions

A shade of difference

Are the figures exactly the same colour?

Compare the shades of the grey figures. Then slide the display surface and see what happens to them.

The figures are the same colour. The shade of colour appears, however, to change when the surface of the display is moved.

This is called the colour contrast phenomenon, in which the shade of colour we observe changes in response to the colour surrounding it. When surrounded by a darker colour, the grey lightens and when surrounded by a lighter colour, it darkens. When surrounded by yellow, the figure turns bluish, and violet makes it yellowish. In this exhibit, however, the contrast effect appears to act in the opposite manner. The grey stripes have more contact surface with the colours next to them, but still black seems to cause a darker effect, white lighter, violet bluish and yellow yellowish.

This anomaly can be explained by the Gestalt laws of perception. They refer to perceptual methods which enable us to perceive entities based on individual observations, and to group or select perceptual stimuli from among others. Both the figure and the vertical stripes of the background are entities which guide our interpretation. We interpret the grey figure as a solid surface that is intersected by vertical stripes. On the other hand, we see the grey stripes as a part of the vertical striping. Hence, we are not comparing the grey colour to the colour next to it but rather, to the colour of the vertical stripe that forms a continuation for it. The Gestalt laws of perception concern e.g. the relationship between figure and background, proximity, similarity, continuity, familiarity and common fate.

Designers in different fields utilise these laws of perception in order to create, for example, products that are easy to use and comprehend, or to organise smooth traffic systems.

Nipkow disk

Can an entire image be seen one small hole at a time?

Spin the disk fast and watch.

You see the entire image, although you are actually only seeing one small portion of the image at a time.

You are seeing with your brain. Each hole passes over the image and the image is fed to your eyes point by point and line by line. Due to the afterimage phenomenon, you see a complete image; the visual perception of each part of the image remains in your brain for a sufficient period of time. Paul Nipkow patented this type of disk in Berlin in 1884. It can be used for mechanical scanning.

Nipkow’s invention was an important stepping stone for the development of television: Using light cells, the points visible through the disk can be transformed into an electric current and transmitted as ultrashort waves. The receiver converts the electric current back into visual dots, which shine with a different brightness depending on the intensity of the current, and they reproduce the transmitted image onscreen for viewing.

Straight through the curve

Why does the straight stick need a curved opening?

Swing the stick through the opening in the vertical plane.

The straight stick passes cleanly through the curved opening in the plane.

The straight stick is attached to a vertical axle. The plane is also vertical, but the stick is angled. The ends of the stick are furthest from the axle and the centre of the stick is closest to it. Each of the points on the stick passes through the opening at its own relative distance from the axle. For this reason, the opening in the plane must be curved.

The shape of the opening is a hyperbola. The surface which the straight stick describes as it spins around its axle is a hyperboloid.

It is often difficult to perceive the path that a moving object will take in reality. When moving from one residence to another, you might need several attempts to get the sofas and tables in and out through narrow doorways – and not always do they fit.

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.