Heureka Classics Catalogue

By varying the speed of rotation, can you predict where the objects placed on the spinning table come off?

Slide objects across the spinning table and investigate what happens when you change the speed of rotation. Where do the objects come off? What direction are they moving in?

When the table spins, friction affects an object's direction of motion — depending on the table's speed of rotation, as well as on the object's initial velocity and moment of inertia. The heavier the object, the greater its moment of inertia, and so the smaller the effect of friction. Also, if the object has a high initial velocity, frictional force has little time to affect its motion.

Can you make the tennis ball reach the ceiling?

Pull the cord to drop the Bowling ball and see what happens to the tennis ball in the other tube.

The Bowling ball in the large tube acts like a sting. The same amount of gas, at the same time, has to move through the narrow tube. So, the air speeds up, producing a jet that sends the tennis ball rocketing towards the ceiling.

Can you talk to a friend who is out of earshot?

Whisper into the center of the concave reflector and listen to your friend's reply from the other reflector. Amazingly, you can hear each other clearly across a crowded noisy room.

The secret is in the shape of the reflector: it's a parabola. The parabolic reflector projects sound from its focal point outwards, in a bundle of parallel waves. And these are received by the other dish and reflected back into its focal point — where your friend is standing.

Which ball bounces the highest?

Lift the two stacks of balls along the cables and let them drop from the same height.

According to the law of conservation of momentum, the total momentum of objects before and after they collide is the same. When the smallest ball is on top, it bounces much higher than its original height: it's projected by the momentum of the larger ball. But when the smallest ball is at the bottom, its momentum is not great enough to lift the larger ball off the top of the Super Ball stack.

Does light disappear into a black hole like a ball into a funnel?

When you set the ball spinning, it orbits towards the center of the funnel. The closer it gets, the greater its speed. This funnel is like a black hole in outer space. The funnel represents the curvature of space, and the ball is an object being sucked into the hole's center of gravity.

When a photon of light comes within a black hole's 'event horizon' it cannot escape the hole's pull, which is why black holes cannot be observed directly.

Does the sculpture defy the law of conservation of momentum?

When you spin the rattleback one way, it goes for a long time until friction stops it. But when you spin it the other way, it starts to rock and then — without you touching it — starts turning round.

The rattleback is a special shape. It is flat on top, with an asymmetrical ellipsoidal bottom. The top and bottom axes are not parallel so the rattleback is predisposed to spin in one direction. When you spin it clockwise, it slows down and starts rocking. Then the rocking motion is transferred into spin in the preferred (anticlockwise) direction.

Does the double cone defy gravity?

The double cone appears to defy gravity by rolling uphill. In fact, because of its geometry, its center of gravity is descending, so as the track widens it is actually moving downwards.

This experience is a dynamic paradox — an apparent violation of the Law of Universal Gravitation. But a more detailed examination quickly corrects this impression.

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

When the disk spins fast enough, you see the images on both sides of the disk in such rapid succession that the brain combines them into a single image. This phenomenon is known as an 'afterimage'.

You can experience a strong afterimage by staring at a bright light and then turning to look at a pale-colored surface. After about one second, the afterimage turns into a 'negative' in its complementary colour.

Why does the series of images appear to be moving?

Spin the zoetrope and peer through the slits: the pictures begin to come to life and look like a short film. You will also notice that the story is looped — it always begins and ends with the same image.

When the images in a series follow each other closely, your brain perceives continuous motion, even though each image is actually an individual still picture.

'Zoetrope' means 'wheel of life' and is the name it was given by the Frenchman Pierre Desvignes who first marketed it in 1867.

Can you make an image appear from nowhere?

Wave the wand rapidly: an image appears.

In fact, the wand only reflects — one strip at a time — sections of the image. But your brain stores its perception of each Strip just long enough to join them together effortlessly and so you see a complete image.

Can you stop the bell ringing without touching it?

When the Dome is filled with air, you can hear the bell clearly. But when there is less air in the dome, the sound becomes muffled.

Sound travels as a wave of vibrating air molecules: as the wave moves, the vibrations reach your ears. In a vacuum, there are hardly any molecules to vibrate, so sound cannot travel.

What does the shadow reveal?

Look at the sculpture and its shadow. As the sculpture spins, you'll see the faces of a man and a child, and two birds.

When a three-dimensional object blocks the passage of light, it creates a two-dimensional shadow.

Looking at a shadow, we try to find something meaningful. We search for identifiable, familiar elements. Then our brain fills in the missing bits. Because human faces are so familiar and important, we are particularly good at recognizing them.

Which are the same colour? Which difference?

Compare the adjacent figures, then slide the display to check their true color.

This is the 'colour contrast phenomenon', in which the color we observe changes according to the color around it. When surrounded by a Darker colour, the gray lightens. When surrounded by a lighter color, it darkens. A red background gives the figure a greenish tint, green produces a reddish tint, and a blue background gives a yellowish tint.

But color is also a question of the eyes' photoreceptors. So, color perception is the result of both our brains and our eyes.

How can a bar feel hot to one hand and cold to the other at the same time?

Your skin is sensitive to heat at temperatures around 35–45°C: compared to this, the middle bar feels cool. And it's sensitive to cold at temperatures of 15–35°C: compared to this, the middle bar feels warm. Cold receptors are also activated if the temperature rises above 45°C. So, an extremely hot stimulus can produce a paradoxical cold sensation.

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

Aha! The balls are exactly the same weight, but the smaller one feels heavier. Why is this?

Everyday experience tells us that larger objects are heavier and we'll need more muscle strength to lift them. This is known as a cognitive illusion.

Imagine working at an airport, lifting suitcases onto a conveyor belt. How would it feel if the largest suitcase was empty? What if the smallest was full of bricks?

What types of particles are constantly passing through us?

Examine the cloud chamber and the tracks that appear inside the chamber. What causes the lines to appear? What can the lines tell about our surroundings?

The streaks appearing in the chamber are primarily caused by cosmic radiation arriving from outer space. The Cosmic rays create a trail of ions in the cloud chamber and the alcohol vapor condenses around the ions as a visible trail of tiny droplets which we can see. It is possible to observe different types of particles such as muons, electrons, and alpha particles.

Do the big bubbles or smaller ones rise faster?

The bubbles rise because they are lighter than the silicone oil around them. They are lifted by the force of buoyancy and slowed by viscosity. Buoyancy depends on the bubble's volume. Viscosity depends on its surface area. When a bubble's diameter increases, its volume increases relatively more than its area, so the buoyancy increases faster than the viscosity opposing lift. Thus, big bubbles rise faster than small ones.

How does a straight stick go through a curved slit?

The plane surface is vertical. The straight stick is attached to a vertical axle, but is set at an angle to it: the ends of the stick are furthest from the axle. For the stick to pass through, the slit in the plane must be curved.

The shape of the slit is a hyperbola. The surface which the straight stick describes as it rotates around its axis is a hyperboloid.

Do two wheels with the same shape rotate at the same speed?

Both wheels are the same size and same weight. But one always turns faster and beats the other. What's the difference between them?

One of these wheels has a heavy center and the other has a heavy rim. The closer the mass is to the center of rotation, the lower the object's moment of inertia, and the faster it spins. That's why the wheel with the heavier center always wins the race.

Which billiard ball reaches the bottom first?

The steeper the track, the faster the ball accelerates. The curved track is much steeper at the top than the straight track. This produces rapid acceleration and ensures the ball's victory, even though the distance traveled is longer than on the straight track.

This particular curve is a cycloid — the path along which an object rolls fastest from top to bottom under the effect of gravity.

Are ships sinking in the Bermuda Triangle?

Press the button to produce air bubbles. As the bubbles reach the water surface, the ship begins to sink. This happens because the large number of bubbles decreases the mean density of the water — the ship then loses buoyancy and sinks.

This effect might be the reason for mysteriously disappearing ships and airplanes in the Bermuda Triangle. However there seems no reason for methane gas to be discharged more often here than in any other region with a volcanically active seabed. Mysterious indeed!

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

Spin the disk fast and watch. As each hole passes over the image, it is fed to your eyes point by point and line by line. Due to the afterimage phenomenon, you see a complete image. Nipkow's invention allows you to see with your brain.

Are the figures exactly the same colour?

Compare the gray figures. Then slide the display and see what happens.
The figures are actually the same color — they only appear to change.

What happens here is opposite to the color contrast phenomenon. Black seems to cause a Darker effect, white lighter. This is explained by Gestalt theory, by which we see the gray stripes as part of the vertical striping — we don't perceive separate components, but make a perceptual construction of a single whole.

Which way is the head spinning?

The head always spins in the same direction. But as the convex side changes to the concave side, the direction of spin appears to change.

We do not observe the world passively, but rather, our brain interprets the information sent by our Senses and draws on previous experience. Real human faces are convex. So, as we watch the spinning head, we ignore the cues telling us that one side is concave. Instead, we 'see' a change in the direction of spin. The illusion is heightened by light and depth perception.

What keeps the ball floating in the air?

Try to take the ball from the air stream and put it back. Try to disturb the stream from different directions and observe how it affects the ball.

The ball finds the equilibrium point of three forces affecting it. The rush of air pushes the ball away from the tube; Gravity pulls the ball downwards simultaneously causing the flow to be faster above the direction of the stream than under it. According to Bernoulli's principle, the faster moving air is at lower pressure than on the opposite side. The higher pressure forces the ball back in. The stability is so strong that the ball can be lightly nudged, and it will still return to its equilibrium position.

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

Pull the leveler to get the nails out. Try with your finger how sharp the nails are. Go lie on the bed and lift the nails again. How does it feel?

The weight of the whole body is distributed evenly to so many nails that the pressure on a single nail is very low. In the end your weight is distributed to approximately the same area as the soles of your feet when you stand up.

How to make a physical 3D animation?

Through the slits of the zoetrope, 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. French Scientist Étienne-Jules Marey (1830-1904) invented a camera with Magazine plates that recorded a series of Photographs to study birds. This is one of the first movie cameras. With the help of the photos, he studied the motion and illustrated it by placing sculptures he made inside a zoetrope. The sculptures are copies of those found in Marey's zoetrope (1887), which is part of the collection at the National Technical Museum in Prague.

Why does sound frequency fluctuate with movement? Listen to what happens to the sound before and after you spin the disk. Can you hear how the frequency begins to fluctuate around the original pitch of the sound without movement? This phenomenon is called the Doppler effect, and it concerns all wave motions. The wavelength will get shorter when the source of the wave is getting closer and longer when the source is moving away from the observer.

What makes a vortex?

Adjust the rotating speed of the propeller in the tank and examine how the vortex is formed. Pressure on the surface equals atmospheric pressure. When the water speed increases a pressure difference between the atmospheric pressure and the water surface forms. The Deeper the vortex hole gets, the larger the hydrostatic pressure is, and the higher the water speed must be in order to keep the balance. The water level settles at the level where atmospheric pressure, impact of the water speed and the hydrostatic pressure are in balance.

Is it possible to see sound? Change the vibration frequency by pressing the button. Listen and watch the sand patterns on the plate.

When the plate vibrates the sand collects to the areas where the standing wave has minimum amplitude. These areas are called nodes. When carefully calibrated resonance frequencies are played to vibrate the plate, sand forms various symmetrical patterns depending on the vibration. The lowest frequencies have fewer nodes keeping the patterns simple, while higher frequencies produce more complex patterns.

How does the Bubble ring stay in its shape and not break up?

Blow air through the tube by pressing the button. Observe how the released air behaves in the cylinder.

A fluid donut can be created by blowing fluid through a round hole of appropriate size. Water flows upwards inside a rising ring and downwards outside the ring. The pressure differences keep the ring intact and the rings move without interference in still water. When colliding with water currents or the surface the shape of the ring will change, finally breaking into smaller bubbles. The same phenomena can be observed with other fluid combinations. Even air can form an Invisible ring inside air.

Why does the ball fall slowly between the copper plates?

Pull the magnetic ball up with a string and let it fall freely. Observe how the ball behaves when falling.
Copper is a non-magnetic metal with high electrical conductivity.

When a magnetic ball is dropped between the copper plates, the moving magnetic field creates an Eddy current in the copper. This is called electromagnetic induction. The Eddy current generates its own magnetic field which interacts with the balls own magnetic field slowing it down.

How do you convert movement to electricity? How do you convert electricity back to movement?

Turn one of the cranks. Observe what happens. Turn the other crank. What happened now? What happens if you change direction?

A Dynamo is a device that generates electricity from movement by moving copper wire in a magnetic field created by permanent magnets. A motor does exactly the opposite. In its simplest form they are actually the very same device; if you feed electricity to a dynamo, it is actually a motor. If you change the direction of the rotation, the polarity of the electricity will also change.

How to create a Lightning bolt?

Turn the crank to charge the capacitors. Observe what happens between the tips of the metal rods. When the crank is turned, the metal brushes collect electrical charges from the strips located on the discs. The charge increases when the discs are rotated in opposite directions. The collected electric charges are stored in two containers referred to as Layden jars which work as a capacitator. One container has a positive charge, whereas the other has a negative charge. When the difference in charges is large enough an electrical breakdown happens through the air, which can be observed as a lightning bolt between the metal rods.

Why does the small ball fly in the air?

Turn the crank and observe what happens to the small ball. Why does the ball float and why does it drop? By turning the crank, you generate a positive charge in the large ball and the small ball touching it. At the same time the medium-sized ball receives a negative charge. Identical charges repel each other causing the small ball to fly in the air. When the voltage between the large ball and the medium-sized ball becomes high enough, it will discharge as a Lightning bolt between the balls.

Can you wait for an eternity? Observe how fast the cogs are moving. Can you find the last one you can see moving? Can you guess which one of the cogs will take a day, a year, or 10 years to make a full revolution?
The motor rotates the first cog 138 rotations per minute. Each smaller cog turns the next large cog, where the rotation speed of the next cog is one tenth of the preceding cog. Repeating this 18 times, the time it takes for the last cog to complete one full revolution equals the age of the universe.

How can sailboats sail against the wind?

Adjust the sailing direction and sail angle. Can you find a good direction and sail angle to sail against the wind? How is this possible?

When sailing in the direction of the wind, the sails are set to optimize the push of the wind. When sailing towards the wind the Sails are set to redirect the wind towards the back of the boat. The keel of the ship prevents the ship from being pushed sideways by the wind. The point Deepest towards wind where you still can sail is called close hauled.