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.

 

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Funny but rather noisy about Acrhinmedes principle

Zoetrope

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.

   

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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.

Freezing burn

Can a bar be both cold and hot at the same time?

Grasp the outermost bars and hold on to them for a minimum of ten seconds. Now grasp the centremost bar with both hands.

The room-temperature bar in the middle feels hot to one hand and cold to the other.

While you were holding onto the outermost bars, the cold and heat sensitive receptors in your palms adapted to their different temperatures. The room-temperature bar then felt different to each hand, because of the way that the receptors reacted to the change in temperature; for one hand the change was cooling and for the other, warming.

The receptors on the surface of the skin that are sensitive to heat only produce impulses at temperatures of 35–45°C. As the heat increases, the heat-sensitive pain receptors begin to work at the same time as the tissue begins to be damaged.

The receptors that are sensitive to cold temperatures react at temperatures between 15–35°C. They are also activated if the temperature rises above 45°C. Contact with an extremely hot stimulus may produce a so-called paradoxical cold sensation.

Both heat-sensitive and cold-sensitive receptors adapt within a few seconds in the same manner as most sensory cells. This is seen, for example, in the way that our skin adapts to the feel of a hot bath or a cold pool.

Indistinguishables

Can you see a difference between the colours of the figures?

Compare the adjacent figures in terms of their shades of colour. Then slide the display surface over them to check their true colour.

In two of the pairs, the colour of the figures is the same, even though they appear to be different. In one pair, the colours are different even though they seem to be the same.

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. A red background gives the figure a greenish tint, green produces a reddish tint and a blue background, a yellowish tint. The cause of the phenomenon is not fully known. On the cellular level it involves a stimulation of the sensory cells on our retinas that prevents the activity of the adjacent cells. However, the illusion is also the result of other higher level perceptual processes.

Normally, changes in colours result from changes in the quality or amount of light entering our eyes. With the three types of cone cells on our retinas we perceive short wavelengths of light as the colour blue, medium wavelengths as green and long wavelengths as red. Other colours are created through the simultaneous activity of these three cell types. Colours are, thus, a product of our sight and our brain. The different materials in our surroundings simply reflect or absorb light in different ways.

How we see things, depends up many things. If a born blind person gets his ability to see later, he usually can not interpret his vision, because there are no seeing memories in his brain.

Revealing shadows

What does the shadow reveal?

Examine both the sculpture and its shadow on the wall. What do you see?

As the sculpture spins, the shadow appears to form the faces of a man and a child, and two birds.

A shadow is created when an object blocks the passage of light. The parts of the sculpture that are blocking the light create the area of the shadow, a two-dimensional surface. While the shape and size of the shadow are determined by the object itself, they are also affected by the distance of the light source from the object, and the angle at which the light hits the object.

The shadow and light areas created by the sculpture together produce the recognisable figures we see. As we are looking at the shadow, we try to formulate significant and meaningful interpretations of what we see. Once we have located a sufficient number of identifiable and familiar elements in the shadow, our brain fills in the missing pieces around them. Human faces are one of the most familiar and important shapes for us, so we are particularly skilled at recognising them.

One Finnish New Year’s Eve tradition is to melt tin and use the casting to make predictions for the new year. When making these playful predictions, some choose to use the shadow the cast tin creates, while others make interpretations of the casting itself. The tradition of making predictions based on metal castings is common to many countries and has been practiced since the classical period.

Magic wand

Can you make an image appear from nowhere?

Wave the wand up and down rapidly over the line marked on the table.

The motion of the wand makes an entire image appear.

The wand reflects, one width at a time, sections of an image that is projected over the line. Our sensory system, however, stores the visual perception of each width for such a length of time that we effortlessly perceive the images as a single entity.

Move the wand at different speeds and notice how the speed affects your perception of the image. At what speed does the illusion of a complete image break into individual streaks of light with no meaning?

Normally, we see images projected on a screen at the movie theatre or in a lecture hall. Images can also be projected onto other materials, such as water, steam or fog, as long as they reflect the light sufficiently.

Thaumatrope

Can you see both sides of the disk at the same time?

Spin the disk and focus on the image.

When the disk spins fast enough, you see the images on both sides of the disk in such a rapid succession that your brain combines them into a single image.

Since the previous image remains in the retina and brain for a short time, there is time for a visual perception of the following image to be created in the brain at the same time. As the spinning continues, you now see both images continuously superimposed, although they are actually on opposite sides of the disk and are not, in reality, simultaneously in our field of vision. This phenomenon is called an afterimage. All of the moving images we observe are based on the afterimage phenomenon. The thaumatrope or “wonder turner” was introduced in England in 1825.

A strong afterimage can be experience by staring at a source of light and then turning to look at a light surface. After about one second, the afterimage turns into a “negative”, or, in other words, its complementary colour. The afterimage may, in some cases, be irritating, but usually we do not pay any attention to afterimages.

Capturing movement

How does a bird fly?

Look into the zoetrope, first from the side and then from above.

Through the slits, you can see a 3D animation of a flying seagull. From above, you will notice that the illusion is created by ten separate sculptures that depict the different phases of the wing strokes.

Human beings are not able to detect details in rapid motion. For example, the debate about whether or not all of a galloping trotting horse’s hooves lift off of the ground at the same time was not solved until 1877 using the photo series taken by Eadweard Muybridge. It was discovered that a horse is, indeed, entirely off the ground for a second when trotting.

The French Ètienne-Jules Marey (1830–1904) studied the physiology of living creatures and that which the eye does not have time to detect. His chronophotographic gun (1882) took 12 consecutive frames per second all on the same picture. With the help of the photos, Marey studied motion, but also illustrated it by placing sculptures he made inside a zoetrope. Marey’s gun was actually the first movie camera.

These sculptures are copies of those found in Marey’s zoetrope (1887), which is part of the collection stored at the National Technical Museum in Prague.

High speed cameras will allow us to photograph at a rate of up to 100,000 frames per second. This method is used to examine the details of movement, and is helpful, for example, in quality control; the camera can pick up deviations in a rapid production process.

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.

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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.

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Slow motion

Racetrack

Which ball will reach the bottom first?

Place the balls at the upper end of the tracks. Set the balls rolling down the tracks at the same time.

The ball rolling down the longer, curved track will be the first to reach the bottom.

The speed of both balls as they reach the bottom is the same, because they receive the same kinetic energy as they move the same distance on a vertical plane. The ball rolling down the curved track is faster at the start, because its speed of acceleration along the steep track is greater. Due to this fast initial acceleration, this ball will have a faster time, even though its acceleration at the gently sloped end of the track is slower and its track is longer than the straight track. In this race, it would be in vain to put your hopes in any final sprint for the finish line!

A track along which an object will descend the fastest or roll, as a result of gravitational pull, the distance between two points of differing heights without any frictional resistance is called a brachistochrone curve. The mathematical shape of the curve was studied – and explained – already during the 17th century by famous scientists including Newton. The curve is known as a cycloid.

A point on the circumference of a rolling circle draws a cycloid. If we attach a small lamp to a bicycle tire and drive with the bike in the dark, a camera that is set to a slow shutter speed will take an image in which it appears that the light from the lamp forms a cycloid pattern in the air.

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Cat Matikainen

Racing wheels

Why is one wheel faster than the other?

Place both wheels at the top edge of the angled plane and release them simultaneously

The same wheel will always win the race. Can you find any differences between the wheels?

The wheels are the same size, the same weight and are made from the same materials. The only difference is the placement of the weight. One of the wheels has a heavy centre and the other wheel’s weight is located toward the outer rim. For this reason, the wheels have different moments of inertia.
The moment of inertia signifies the inertia of the object as it rotates, or, in other words, its ability to resist any change in the rotational speed. The wheel whose weight is located around its outer rim has a higher moment of inertia. Therefore, it accelerates slower as it rolls and falls behind the other wheel whose weight is located closer to its axis of rotation.

Many public bathrooms have very large toilet paper rolls in their stalls. Due to their high moment of inertia, these rolls spin slower as the paper is being pulled off the roll. If the paper is pulled too quickly, it will tear too soon. A knowledge of physics is an asset in this situation as well. In order to get a suitable amount of paper, it should first be pulled off of the big roll slowly. Then the paper can be torn off with a rapid tug without needing to use your other hand to hold the roll steady, as is necessary with a smaller roll.

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Cat Matikainen

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.

Visualising cosmic radiation

What types of particles are constantly passing through us?

Examine the cloud chamber and the tracks that are visible inside the chamber.

The flashing streaks are primarily the tracks of cosmic radiation arriving from outer space. The tracks of the particles become visible in the alcohol fumes of the cloud chamber. When the particles collide with the fumes, they condense into small droplets. Part of the radiation in the chamber originates from the Earth.

Cosmic radiation is comprised of high-energy particles originating from the Sun and exploded stars. Altogether 90 % of the particles are protons, 9 % are alpha particles and 1 % represent beta particles and the nuclei of heavier atoms. Cosmic radiation is only one part of the ionizing radiation which human beings get from nature. Its amount is minor in relation to the other radiation that we get, such as the radioactive radiation from radon gas in the ground or the radiation from x-ray machinery used for medical purposes. The magnetic field and atmosphere of the Earth almost entirely prevents any cosmic radiation from reaching the Earth’s surface.

Flight personnel may receive up to 10 times more cosmic radiation than the rest of the population. Its health impacts are, however, quite minimal, even though it may be the most significant source of radiation for flight personnel.

For whom does the bell toll?

Can you make the bell stop ringing without touching it?

Press the button for the bell inside the dome. Then, suck the air out of the dome by pressing the green button, and ring the bell again. You can return the air to the dome by pressing the red button.

When the dome is filled with air, the sound of the bell can be heard quite clearly. As the amount of air decreases, the sound becomes muffled and eventually inaudible.

Sound is a mechanical wave motion that requires a medium in order for it to travel. The source of the sound makes the air molecules vibrate and the vibration is further transferred through the molecules to your ears. Sound cannot travel or be heard in a vacuum, because there are no particles in a vacuum to transfer the sound.

In space films, there are sometimes battle scenes in which the characters are shooting with laser guns. The laser beams flash back and forth and the din of the battle is deafening. These scenes are made in accordance with the laws of drama rather than the laws of physics. There is no air in outer space, so the beams of the lasers would not be visible from the side; air molecules are required in order for the beam to scatter to the sides. As there is no medium to transfer the sound either, the battle would, in reality, be completely silent.

Hydrogen rocket

Can you use water to launch a rocket?

Begin the test by turning the handle. The lights will turn green when the rocket is ready to launch. Press the button to initiate the countdown.

The rocket launches into the air once the gases generated by the turning of the handle are ignited.

The electric current created by the turning of the handle breaks down the water molecules H2O into gaseous elements, hydrogen (H) and oxygen (O). This chemical reaction is endothermic in nature, in other words, it requires energy, which in this case comes from the muscles of the person turning the handle. The reverse reaction, in which the hydrogen and oxygen are fused, in other words, the combustion of hydrogen into water, is correspondingly exothermic, meaning that it releases energy. As the gas mixture explosively combusts and turns into water vapour, pressure forms in the combustion chamber. The pressure releases as the combustion gases flow with force out from the end of the rocket, thereby causing the rocket to lift.

The thermal value of the burning hydrogen in relation to its mass is very high. It is about three-fold in comparison to that of petrol. Hydrogen serves as the fuel for space rockets, because any extra weight in the rocket would be detrimental to its takeoff. The hydrogen, and the oxygen required for it to combust, are placed into the rocket as cooled liquids, each in its own separate tank.

Stubborn boat

Does the sculpture defy the laws of physics?

Set the boat spinning first anticlockwise and then clockwise. Watch closely the direction in which the boat rocks.

When you spin the boat anticlockwise, it spins for a long time and eventually stops. When you spin the boat clockwise, however, it begins to rock longitudinally, the spinning slows rapidly and it changes its direction to rotate in an anticlockwise direction.

When an object is spun around an axis whose rotational inertia is other than the maximum or the minimum, it becomes subject to torque and begins to rock. Our stubborn boat is slightly asymmetrical and, on its base, it spins around an unstable axis. For this reason, it begins to rock as it spins both longitudinally and laterally. The rotating direction determines with of these two unstable motions will be dominant. Here, spinning the boat clockwise will cause more rocking in a longitudinal direction, while lateral rocking is greater when the boat is spun in an anticlockwise direction. Longitudinal rocking affects the spinning motion more and, in the end, when combined with friction, it will alter the spinning direction. At the same time, the rocking motion changes to a crosswise motion. The first attempts to explain the physics of the stubborn boat were conducted more than a century ago, but the behaviour of a spinning boat still remains without a definitive physical explanation.

The phenomenon is similar to that of a poorly balanced car tyre. It also begins to wobble if the direction of the spinning axle is slightly different that the natural direction of the spinning axle of an asymmetrical tyre.

Links

Slow Motion

Black hole

Does the black hole swallow everything?

Set the ball spinning into the funnel.

The ball travels in accelerating speed toward the throat of the funnel.

In our model, the funnel represents the curvature of outer space caused by the black hole, the throat is the black hole itself, and the ball is an object being sucked into the hole. Due to the drastic curvature of space, the force of gravity around the black hole is especially strong. Once an object enters into the area within the stationary limit it still has hope. Some of the objects will be hurtled out of the range of the black hole, while some will be sucked into its centre, the singularity. Beyond the event horizon, not even light will be able to escape the gravitational field of the black hole. This is the reason why a black hole cannot be observed other than indirectly.

In time, the speed of satellites orbiting the Earth in outer space slows down due to the friction present in the uppermost atmosphere. This friction will eventually cause the satellites to drop back to Earth. The limit of the atmosphere and the gravitational pull of the Earth are as fateful a combination for satellites as is the event horizon of a black hole. Those objects that venture beyond the borderline are facing unavoidable destruction – sooner or later.

Super Balls

Which balls will bounce highest?

Raise the stacks of balls up and release them so that the balls will fall as straight and freely as possible, without shaking the cables. Do not throw the balls upwards.

In the stack in which the largest ball is the uppermost ball, the balls will hardly bounce at all. In the other stack, the uppermost small ball in the other stack bounces metres in height.

As the stack of balls collides with the base, the biggest ball at the bottom of the stack bounces upwards. A split second later, it collides with the next ball. At the point of collision, the momentum of the larger ball transfers to the smaller ball to such an extent that the bounce speed of the smaller ball is nearly tripled. When the same is repeated two more times, the speed of the smallest ball could theoretically be up to 27 times (=3x3x3) greater than the falling speed of the balls.
The height of the upward bounce is proportional to the speed when squared. If the balls were dropped from a height of one metre, the smallest ball would bounce to a height of 27^2 = 729 metres – in theory that is, when friction, air resistance and the balls’ only partial elasticity are left out of the equation. During the collisions in the second stack, the momentum of the uppermost larger ball is downward. For this reason, the balls aim downward as a result of the collision.

When a large and small object collide elastically with one another, the smaller object gets a larger speed than the combined speed of both objects. The hardest trajectory in football is achieved when a player kicks at a ball coming towards him.

Links

Super Balls in slow motion
A short history and physics of Super Ball
Another short history and properties of Super Balls

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.

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Cat Matikainen

At the focal point

Can you find the focal point of the mirror?

Place your hand in front of the mirror and test the warmth reflected from the mirror at different points on the mirror.

The heat radiation is reflected most strongly at the mirror’s focal point. The focal point can be located with the help of both light and heat.

The light and heat radiating from a heat lamp are reflected off from the concave mirror so that the rays intersect close to the focal point. They do not meet at any one exact point, because the rays hitting the mirror are not parallel. The heat from the rays of the Sun can be utilised effectively with the help of large parabolic mirrors, if a high temperature is required at a specific point. The positive aspect of this system is the cost-free energy. The negative side is that the mirrors would have to rotate at the exact same rate as the Sun in order to ensure that the rays would always be reflected at the same point.

Archimedes is told to have lit Roman ships on fire with the help of concave mirrors at the siege of Syracuse. On the basis of practical research, this story has proven to be a myth. On the other hand, solar cookers that work using mirrors do actually work and can be used, for example, at cabins. As development aid, Finland provides solar cookers to many countries in which they are reducing the use of firewood and logging. They also relieve the workload of women responsible for the collection of firewood.