Archiv der Kategorie: Allgemein

The shoebox speaker

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written by Michael Himmelbauer

By using a common shoebox, enjoyable music with a high sound quality can be played. What sounds to be unimaginable, can be realized with some components you may have at home, but can also be found in the physics room:

  • an amplifier (the older the better)
  • two cables
  • a magnet (the stronger the better)
  • a coil (or a long piece of wire and a cylinder (for example from toilet paper))
  • the star of the experiment: a shoebox (without the cover)
  • a device with a plug to play music
  • and of course: enjoyable music (for instance on your mobile phone)

First of all, you have to glue the coil (or the wire wrapped around the cylinder) onto the bottom of the shoebox. Furthermore, the cables have to be plugged into the amplifier (take care that you use the correct ports) and have to be connected to both of the ends of the coil (no matter whether it is bought or a self-made one) as shown in the pictures:

Moreover, you have to select a relaxing song to play (due to the wide range provided on the internet, this could be the most difficult part of the experiment). In order to broadcast the music, you have to connect your mobile phone, computer or MP3-player to the amplifier (either via another cable or wireless). As soon as you have started the song, place the magnet in the middle of the coil as shown in the picture:

In case you read the instructions carefully and the cable connection works, you may be speechless at that point as you can hear your favorite song without using a classical speaker (or headphones).

But why’s that? Why can music be played without using speakers?

Admittedly, the shoebox works as a speaker as the mantle of the cuboid replaces the membrane.

In order to understand that phenomenon, we need to take a look at an electro-magnetic force named by the physicist Hendrik Antoon Lorentz. It occurs as soon as a current flows through a conductor. Its direction has an angle of 90 degrees to the direction of the flow and the magnetic field.

And as the amplifier dispenses alternating current (AC), the direction of the flow inside the coil changes constantly and that is why the direction of the Lorentz force changes, too. Subsequently, as the magnet remains at the same place, the coil swings back and forth with the frequency of the flow (that the amplifier dispenses). As a result of that (the coil is sticked onto the bottom of the shoebox), the membrane swings with the same frequency. Moreover, the swinging membrane spreads waves into the air that get to our ears where they are converted into an electric signal that is forwarded to the brain (ask a biologist if you’ve got any questions concerning the processes inside the human body).

To convey the theory more easily, I made a drawing that outlines the effects of the currency to the coil and depicts the formation of the acoustic waves:

In case you are curious, you could also use the speaker for playing spoken records (for instance a speech from a well-known politician or the latest news program). While listening to the wisely chosen words from a famous person, you may be amazed by the high quality and the clear sound.

Another usage of the self-built speaker could be its opposite, a microphone. When recording waves, the Lorentz force is considered to move the electrons inside the wire and that is the reason why an electric voltage is induced (to try that, you could conduct an experiment on your own that is similar to the described one).

To sum up, it can be mentioned that with the help of a shoebox and some other components, but without a speaker, music can be played and quite some things can be found out about the characteristics of the acoustic waves that enable us to understand each other properly.

source:
Putz, Bruno; Jahn, Brigitte: Faszination Physik 7 bis 8. Lehrplan 2018. Linz: Veritas 2019, p. 13

fotocredit: (c) by Michael Himmelbauer

one laser pointer, nine rays

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written by Michael Himmelbauer

A usual laser pointer emits one ray, but nine can be seen on the wall after the ray passes a special optical instrument. What sounds to be impossible, can be realized with the help of some components that you may not have at home, but fortunately can be found in the physics room:

  • a laser pointer (for example a green one)
  • a bar grid
  • two tripods
  • for measuring: a measuring tape

First of all, you have to set up the components as shown in the picture, preferably in front of a white wall in a rather dark room.

When you switch on the laser pointer, you may be surprised by the fact that you can see nine rays on the wall, although only one ray is emitted by the laser pointer. At that point, you might want to ensure that it works properly, but please do NOT look directly into the light of the laser pointer for safety reasons (at least if you don’t want to damage your eyes forever).

Now you may ask yourself: Why’s that? Why can nine times as many rays be made out even if only one is emitted?

Therefore, we need to take a look at the structure of the bar grid. It consists of several lines into horizontal and vertical direction printed onto a disc of glass. The label „200 lines per millimeter“ means that there is a space of 0.000005 m between each of the lines.

For simplifying the process, we need to assume that the bar grid doesn’t feature several, but only two gaps (with the same width as above). When an electromagnetic wave passes these gaps, it turns from a straight to a circular wave. After that, the amplitudes of the waves interfere with each other, and those interferences are spread until they get to the wall. There, they are reflected and the light (again in the form of waves, but with a much lower density) gets to our eyes.

For illustration, I made a drawing to convey the theory:

The next question that comes to your mind might be: Can this theory also have benefits when using it in a practical way?

As a scientist, I say: Yes, it can. For instance, we can take usage of it when calculating the wavelength of a specific color (and that’s the reason why we conducted this experiment).

For simplification, we have to estimate that the sine of a small angle is has almost the same value as the tangent of the same angle (supported by the fact that for angles like that, the cosine is almost 1 and the tangent is calculated by the quotient of sine and cosine).

According to the drawing above, we can make up the following equations:

And as we are able to measure the distance from the tripod to the wall (2.08 m), the distance of the lines on the bar grid (0.000005 m) and the space between two points on the wall (0.225 m), we are able to do the following calculations easily:

That means that the light of the green laser pointer we used in the experiment has a wavelength of approximately 541 nanometers.

Another practical application of the effects of interference is used in clubs for the disco lights, featured with a small engine that slowly rotates the light emitting diode (LED). That is why some impressing patterns can be seen on the walls and on the ceiling.

To sum up, it can be mentioned that with the help of a laser pointer, a bar grid and two tripods, the wavelength of a specific color can be calculated and quite some things can be found out about the spreading of the electromagnetic waves that light up our everyday life.

source:
Putz, Bruno; Jahn, Brigitte: Faszination Physik 7 bis 8. Lehrplan 2018. Linz: Veritas-Verlag 2019, p. 68-69

fotocredit: (c) by Michael Himmelbauer

The liquid powders

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written by Michael Himmelbauer

Firstly, you put a few grams of two white powders into a beaker and after stirring for a minute, it turns into a turbid liquid. What sounds to be impossible (or fake news, as we would call it), can be realized with the help of some components you may not have at home, but luckily can be found in the chemistry room:

  • two beakers
  • a spoon
  • a scale
  • a brick of wood
  • the stars of the experiment: 15 grams of Barium hydroxide (Ba(OH)2) and 5 grams of Ammonium thiocyanate (NH4SCN)
  • some water (H2O)

First of all, we weigh the required amount of the two powders with the help of the scale and put them into the two beakers as shown in the picture:

Next, we do something you better should not do if you don’t know what’s inside the beakers (fortunately, I know what I’m writing about): We pool the two powders into one beaker (in case you’ve got two different sizes: put it into the bigger one) and mix them with the help of the spoon. After some time stirring (and maybe a hurting arm), we recognize that inside the beaker, the powders disappeared and were replaced by a turbid white liquid. Furthermore, the fluid smells strange. In case you touch the bottom of the glass, you may find out that it feels cold (although the windows and the fridge are closed, so the cause of the low temperature is the beaker – even if you don’t believe it).

But why’s that? How can two powders that look almost similar turn into a liquid that stinks and cools down its environment?

To explain that chemical process, we have to take a look at the reaction equation of Barium hydroxide with Ammonium thiocyanate:

Ba(OH)2 + 8 H2O + 2 NH4SCN → Ba(SCN)2 + 2NH3(g) + 10 H2O

According to the equation, the educts Barium hydroxide (that consists of Ba(OH)2 and solid water (H2O)) and Ammonium thiocyanate (NH4SCN) react with each other. The products on the right side of the equation are Barium thiocyanate (Ba(SCN)2), Ammoniac (NH3) and liquid water (H2O). The turbid liquid consists of Barium thiocyanate and water, Ammoniac is released into the air as a gas that causes the unpleasant smell.

And in case you put the beaker onto the wept brick of wood, you might be frightened when you want to lift the glass because you may recognize that the ice-cold beaker sticks onto the brick of wood:

But why can a liquid that consists of two strange powders make a glass stick on a wooden part?

In order to answer this question, we have to know that the chemical reaction described above is considered to be an endotherm reaction as energy (in the form of warmth) is required all the time. This energy is taken from the environment around the powder in the glass, and that is why the glass cools down. And as we all know (or have at least learnt at school), water freezes in case the temperature drops below zero degrees. Caused by the fact that we put some water onto the brick of wood before mixing the powders, the breaker has frozen onto it.

The energy graph (a diagram that shows the amount of energy a substance contains) of an endotherm chemical reaction outlines that the products in the end have a higher level of energy than the educts at the beginning. In order to compensate the difference, energy in the form of heat is required and is taken from the environment.

To sum up, it can be stated that when pooling two special powders into one beaker, their state of aggregation turns into liquid and the required energy can make the glass freeze onto a brick of wood. Both are results that wouldn’t come to your mind when you’re thinking about powders, would they?

source:
Anon.: Entropische Zauberei. https://www.uni-wuerzburg.de/fileadmin/08020000/pdf/erlebnis/endotherm_reak.pdf
[last access: 01.02.2022]

fotocredit: (c) by Michael Himmelbauer

Pans, Heat, and Bonding 

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by Sarah Diregger

While cooking, one can notice that metal becomes hot very quickly and wood or plastic is safer to touch if you’re not in the mood for a 2nd-degree burn. I’m sure everybody knows not to touch the pan while it sits on the stove. But why? What’s the difference between metal and plastic? Why does metal heat up so easily? 

Firstly, to prove my theory that metal heats up faster than plastic I experimented: 

You need a plastic rod, a metal rod, an infrared camera, and warm hands. You hold each rod in your hands for 1-2 minutes. Then you point the infrared camera at the two rods, and you can see the results immediately.  

Here, you can see an image of the two rods next to each other before the experiment: It’s very faint but I think you can make out two different sticks. The left one is metal, the right one plastic. 

This is what the plastic rod looks like after one hand held it: 

This is what the plastic rod looks like after 3 hands held it: 

This is what the metal rod looks like after a you hold it in your hand: 

On the scale at the bottom of the images, you can see which color symbolizes which temperature. Consequently, we can see that before the experiment, both were at about the same temperature. After the experiment, the plastic rod was only heated at the area you held it. However, the temperature of the warm hands spread farther and the area of warmth was greater than the size of your hands. 

The explanation for this phenomenon lies on the atomic level. It’s important to know that atoms form 3 different types of bonds: 

Covalent bond: Bond, in which atoms share electrons 

Ionic bond: One atom gives its valence (outermost) electron(s) to the other atom. Therefore, one atom acquires a positive charge and the second acquires a negative charge. Positive and negative attract each other, leading to the atoms forming a bond. 

Metallic bond: The nuclei (plural of nucleus) of the atoms arrange themselves in a fixed structure, while the negatively charged electrons move freely in between the positively charged nuclei. 

Here is an illustration to help you visualize what this looks like: 

Before I explain further, it’s crucial to know what heat is. Heat is basically the vibration of atoms and molecules within a substance. The more they vibrate, the hotter the substance is. 

We will be focusing on the last type of bond, the metallic bond. Since the electrons don’t have a fixed position within the atomic structure, they can move around more than the electrons in a covalent or ionic bond. If we look at the physical properties of heat, it’s obvious why metals, who have metallic bonds, conduct heat better. The electrons can vibrate easier and it’s easier for them to pass this vibration on to the next electrons. Plastic has a covalent bond. Therefore, the atoms within the polymer (the scientific name for plastic) are tied together tighter and vibrations can’t be transmitted as easily. 

In conclusion, metals transfer heat the best because of the type of atomic bonds they have. The metallic bond allows electrons to move between the nuclei. Therefore, the movement of heated electrons can be conveyed easier than in fixed bonds. Which important lesson do we learn in our day-to-day lives? Never use metal if you want to handle something hot because it doesn’t shield the heat. 

Sources:

https://www.edinformatics.com/math_science/why_metals_conduct.htm#:~:text=Metal%20is%20a%20good%20conduction,of%20their%20energy%20to%20them.

https://www.britannica.com/science/crystal/Conductivity-of-metals

https://www.lernhelfer.de/schuelerlexikon/chemie/artikel/waermeleitung#

https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Chemical_Bonding/Fundamentals_of_Chemical_Bonding/Metallic_Bonding

https://www.chemie.de/lexikon/Metallische_Bindung.html#:~:text=Als%20Metallische%20Bindung%20oder%20Metallbindung,Metallen%20und%20in%20Legierungen%20vorliegt.&text=Sie%20wird%20durch%20Anziehungskr%C3%A4fte%20zwischen%20Metall%2DIonen%20und%20freien%20Elektronen%20verursacht.

https://www.lernhelfer.de/schuelerlexikon/chemie/artikel/metallbindung

[last access: 24.01.2022]

The magic tube

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written by Michael Himmelbauer

I am quite sure you have already seen it or at least heard about it: the magic tube. An optical experiment which is usually shown at the presentation evening of our school. An experiment with the help of which you can impress students from primary school as well as grown-ups (believe me – I am talking out of my personal experience). Although the name sounds complex, it can easily be done at home.

Here is what you need:

  • a transparent plastic tube with a length of approximately thirty centimeters
  • two polarization-filters (honestly, these could be the components the most difficult to get)
  • a screwdriver
  • a ping-pong ball (or something similar)

At first, you have to put the two polarization filters into the tube rotated by an angle of 90 degrees as shown in the picture:

As you may expect, a round black disc can be made out in the middle of the tube. In order to check whether it is real or not, you could use the screwdriver or the ping-pong ball to try if you are able to penetrate the disc (especially young children can be impressed by that). After some tries you might find out that the magic black circle does not really exist or is at least not resistant against your power (caused by their knowledge and perspective, younger students are often confused at that point).

But why can a black disc be seen even if there isn’t anything inside the tube except two plastic films?

First of all, we have to get in touch with the physical discipline of optics. (Now you might ask yourself: What the hell is that?) It is the science of the spreading of light and the effects of different materials on its behavior. Normally, light is a wave spreading from its origin (for example the sun, but also the lightbulb inside the physics room) into all directions. As soon as it gets to the polarization filter, only the horizontal or vertical component of the wave is let through and the other parts are kind of absorbed by the film (at least, it is easy to imagine this physical process like that). To simplify the process, we imagine that light does not exist out of vectors into every direction, but only into the following two directions: horizontal and vertical. As you put the two filters rotated by an angle of 90 degrees into the tube (in case you read the instructions carefully), both one of them only let 50 percent of the entered light pass through. And in case you are able to square 0.5 (I suppose you can or know how to use a calculator), you’ll find out that only 25 percent (so almost nothing) of the original amount of light will pass both films. And that is why a magic black disc can be made out inside the tube. In case you are talented in imagining geometry (or attend geometry class), you might assume that when you look through both filters when being amazed by the effect inside the transparent glass, the waves getting to your eyes (ask a biologist if you have any questions concerning that topic) have to pass both polarization filters and that is why there seems to be an almost black object. The color of the disc can be explained by the fact that if 75 percent of the light is absorbed, the rest (25 percent) appears to be quite dark.

Just in case you are really fascinated by the effects of two toned plastic films, you can try watching reflections of the window on a smooth surface (for instance the floor in the physics room) by looking through one of the polarization filters. While rotating the filter slowly, you might find out that you can see the reflections when holding it in one direction, but in the other direction, they disappear. It’s magic, isn’t it?

To sum up, it can be stated that with the help of two polarization filters, many spectators can be impressed and quite some things can be found out about the characteristics of the magic waves that light up our everyday life.

source:
Anon.: Polarisation von Licht. Einführung. https://www.leifiphysik.de/optik/polarisation/grundwissen/polarisation-von-licht-einfuehrung [last access: 22.01.2022]

fotocredit: (c) by Michael Himmelbauer

Die große Implosion

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von Jana, Pia und Eva

Wolltest du schon immer eine Dose explodieren lassen, aber du durftest nicht? Dann lass sie doch mit unserer Hilfe implodieren. Achtung! Bitte nur unter Aufsicht eines Erwachsenen durchführen! 😉 

Dazu brauchst du:   

  • Eine Dose
  • Eine Wanne mit Wasser 
  • Einen Bunsenbrenner 
  • Eine Zange zum Halten 
  • Evtl. ein Haargummi zum fixieren 

Als ersten Schritt musst du ca. 3 El Wasser in die Dose füllen, die Dose mit der Zange festhalten und mit einem Haargummi fixieren. Als nächstes musst du die Dose über den Bunsenbrenner halten, bis das Wasser darin kocht und dampft. Sobald das der Fall ist, musst du schnell reagieren! Du musst die Dose schnell umdrehen und sofort in die Wanne mit Wasser tauchen und achte darauf, dass die Öffnung der Dose zuerst im Wasser landet. Die Dose sollte dann sofort sehr stark zusammengedrückt werden.   

Was ist gerade passiert?  

Der Effekt, den du dabei gesehen hast, nennt sich Vakuumeffekt. Durch das Erhitzen des Wassers entsteht Wasserdampf, welcher die Luft in der Dose verdrängt. Wenn man nun die Dose abkühlt, kondensiert das Wasser, wodurch ein Vakuum entsteht. Durch den umgebenden Luftdruck wird die Dose zusammengedrückt. 

Hier findest du noch Videos von unseren implodierenden Dosen !

The Hunt for the Shadow of the Flame

Veröffentlicht am von

Sarah D.

It’s Christmas time!! Which means candles. Like…a lot…literally everywhere. Consequently, many candle-related questions come up, such as “Which scent smells the best?”, “Which color should I buy?”, “Can I gift mom with even more candles this year?”. Those are the normal type of questions an average human asks. As scientists, we ask wonderful questions like “How hot is a flame?”, “Can I separate the different chemical components of wax?”, “Do flames have shadows?”. That is the question I want to answer. So, I decided to go on the Hunt for the Shadow of the Flame. Is it real? If it exists, how does it work? 

To demonstrate and help visualize the answer, I conducted an experiment. If you want to reconstruct the experiment you will need a candle, a white sheet of paper, a bright flashlight, and a match to light the candle (unless you want to try it with flint and steel, which I don’t recommend). Firstly, you must darken the room to see results. Then you set the lit candle about 5 to 10 centimeters in front of the white sheet of paper. Take a flashlight that is brighter than the flame and shine it on flame. Now, you will see that the flame itself has a faint shadow, and the air above the candle also has a shadow. It looks like this: 

Ein Bild, das Wand, drinnen, Kerze, Licht enthält. Automatisch generierte Beschreibung

Since the flashlight from the phone wasn’t bright enough, the shadows aren’t very visible. Therefore, I drew a picture of what the shadow is supposed to look like: 

Why do these shadows appear? 

I’ll start by explaining the shadow of the air above the fire: It’s important to know that the candle heats the air above it. The surrounding air remains cold, though. Molecules within hot air move faster than molecules in cold air. Because of the fast-moving molecules, the density in warm air is less than the density in cold air. That means when a light ray moves from the colder air into the hotter air, it goes through a change in the refractive index. (Sarah, what in the gods of physics, is a refractive index?) When a ray of light passes from one medium into another, it’s called a change in the refractive index. It’s important to know, that the light doesn’t get refracted inside the new medium but at the surface of the new medium. In our case, hot air is considered a different medium than cold air, since it has a different density. That means some of the light, which passes through the air above the flame, gets refracted (bounces off and gets redirected) and a shadow appears.  

Next, I’ll explain the shadow of the flame: Burning the wick results in hot ionized gas, burnt carbon fibers, burnt oxygen molecules, and burnt fuel. The resulting substance is also called soot. The soot particles refract the rays of light from the flashlight, forming a faint shadow. Due to the flame being hot, the change of RI also influences the path of the light. 

To sum everything up: Fire produces a faint shadow, and you can also see the hot air above the flame forming a slight shadow. This is because of the change in RI, which causes the refraction of some of the light. The flame itself consists of burning particles. These particles also redirect the path of the flames. 

Fliegende Löffel

Veröffentlicht am von

Von Jana G. und Pia Z.

Wolltest du schon immer einmal das teure Tafelsilber deiner Eltern, für ein Experiment verwenden? Dann nimm dir die Gold- oder Silberlöffel und probiere dieses Experiment aus.                                                                                                

Dafür brauchst du folgende Utensilien:  

  • 2 Löffel (am besten aus Gold/ Silber 😉) 
  • 1 Hand (am besten die, die nur als Deko dient) 
  • Schutzhelm/ Schutzbrille 

Bei möglichen Verletzungen:  

  • Kühlpad 
  • Überraschungsei als Aufmunterung  
  • Nun legst du die zwei Löffel in den folgenden Stellungen:  
Ein Bild, das drinnen enthält. Automatisch generierte Beschreibung
Ein Bild, das drinnen, Tisch enthält. Automatisch generierte Beschreibung

Jetzt musst du nacheinander bei jeder Lagerung auf den unteren Löffel mit der Hand draufschlagen. Wie in folgendem Video ersichtlich ist.

http://www.haberbauer.at/scienceblog/wp-content/uploads/2022/01/20211206_141524-1.mp4

Dabei  beobachtest du bei welcher Lagerung sich der obere Löffel am öftesten dreht. Nachdem wir die Versuche mehrmals ausprobiert haben, sind wir zu dem Schluss gekommen, dass sich bei uns der obere Löffel, wenn man sie so wie bei dem dritten Bild auflegt, öfter dreht als bei den Anderen. Als wir uns jedoch das Lösungsvideo zu dem Versuch angesehen haben, mussten wir mit schreck feststellen, dass unsere Löffel leider ihren eigenen Kopf haben ( im Video war das richtige Ergebnis Bild 1).  

Weil wir diesen schweren Schicksalsschlag nicht so hinnehmen wollten, haben wir die Versuche daraufhin wiederholt und alles versucht, um unser Ergebnis geradezubiegen😉 .  Aus Verzweiflung haben wir dann angefangen, die Löffel zu verbiegen, da uns aufgefallen ist, dass diese im Video nicht so stark gebogen waren, wie bei uns. Dadurch sind  wir auf das Ergebnis gekommen, dass sich bei dem 1. Bild der obere Löffel höher fliegt und sich schneller dreht, je gerader der Stiel des Löffels ist und je steiler die Schaufel.  

Die erste Methode ist am effektivsten, da der obere Löffel zwei Berührungsstellen mit dem anderen Löffel hat und somit mehr Schwung bekommt und höher fliegt. 

Unser Fazit ist, dass dieses Experiment sehr stark von der Form des Löffels abhängt. 

Yay, the water didn’t leak over the rim of my glass!

Veröffentlicht am von

Sarah Diregger

I was pouring a bottle of water into my glass and got distracted for a second. When I looked at the glass of water again, I was really shocked. The water was too much for the glass to hold, but it didn’t flow over on the table. There was this “bubble” of water above the rim of the glass. For the record, it looked really fascinating. So, I wanted to know why this was the case. Magic? Some antigravitational forces? God, having mercy on me, so I don’t have to get a napkin and wipe the table? Like any person in the modern days, I asked Mr. Google for help. He kindly explained to me what the actual, scientific reason was behind it. 

To prove the explanations, I also conducted my own experiment. All you need is a pipette, different sized coins, water and maybe some napkins to dry up your workspace afterwards.  

Ein Bild, das Text, drinnen enthält. Automatisch generierte Beschreibung

Then, using the pipette, I slowly dropped the water onto each coin and counted the drops. 

Type of coin Average amount of water drops 
2 Euro coin 41.3 
1 Euro coin 34.3 
20 Cent coin 34.3 
10 Cent coin 19.7 
2 Cent coin 20 
1 Cent coin 18.7 

Ok, so we’ve established that the amount of water drops depends on the surface area of the coin, but what causes the “bubble” on top to remain a bubble? It’s actually quite logical. 

First of all, it depends on the liquid. In our case it’s water. Water molecules are polar molecules. Now, you might ask yourself, “What the heck is a polar molecule?”. So, first of all, it’s important to know that a water molecule (H2OH2O) consists out of two Hydrogen and one Oxygen atom. The Hydrogen atoms have a slightly positive charge, and the Oxygen atom has a slightly negative charge. That means that the Oxygen atom of molecule A attracts the Hydrogen atom from molecule B. I drew a picture to help you visualize what I mean: 

The bond between the molecules is called cohesion. It keeps the molecules stuck together. Cohesion is strong, but not unbreakable. When the water is dropped on the coin, each water molecule is attracted to each other. Therefore, a thing called the surface tension (the “skin” of the bubble) forms. This is what keeps all of the water together and allows the water to move over the edge of the coin. Once there’s too much water over the edge, gravity overcomes the bubble, and it bursts. 

It is important, though, to remember that this only works with polar molecules. With nonpolar molecules, such as oil, the atoms from different molecules don’t attract each other and therefore, no bubble can be formed. To prove this, I tried the same experiment with the pipette and coin; but instead of water, I used oil. The result looked like this: 

Ein Bild, das Baumaterial, Stein enthält. Automatisch generierte Beschreibung

Once the oil flowed over the edge of the coin, it leaked to the surface of the table. To be honest with you, it was quite a mess. I’m talking from experience, when I say this: Don’t ruin any tabletops because your parents will give you hell for it!  

In conclusion, the mysterious “bubble” on top of the glass (which is actually the surface tension) forms because of the attraction of the atoms between molecules, and the surface tension gives out when there is too much mass over the edge. Then, gravity becomes stronger than cohesion (the force between molecules) and the bubble bursts. But remember, this is only the case when the substance has polar molecules. 

Fotocredit: (c) Sarah Diregger

Das gehorsame Ei

Veröffentlicht am von

von Jana und Pia

Wolltet ihr auch schon immer eine gute Ausrede haben, um im Physikunterricht ein Überraschungsei zu essen, dann probiert doch einmal dieses lustige Experiment aus. Dafür brauchst du nur einen einfachen Faden, ein Feuerzeug, eine Nadel, den Korken vom Vorabend und den Star des ganzen Experiments: DAS ÜBERRASCHUNGSEI 

  1. Der erste und wichtigste Schritt ist erst die Schokolade zu essen und natürlich das Spielzeug zusammenzubauen! 
Ein Bild, das Person, drinnen, Hand enthält. Automatisch generierte Beschreibung

2. Danach müsst ihr vorsichtig die Nadel mit dem Feuerzeug erhitzen (bitte nur unter Aufsicht einer erwachsenen Person😉). 

3. Nun müsst ihr auf beiden Seiten des Plastikeis jeweils ein kleines Loch machen.

Ein Bild, das Person, drinnen, Hand enthält. Automatisch generierte Beschreibung

4. Als nächstes nehmt ihr den Faden und fädelt ihn durch die zwei Löcher. 

Ein Bild, das Person, drinnen enthält. Automatisch generierte Beschreibung

5. Jetzt müsst ihr den Korken waagrecht in das Ei legen, sodass er den Raum gut ausfüllt.  

Ein Bild, das Person, haltend, Hand enthält. Automatisch generierte Beschreibung

6. Wenn ihr nun das Ei zumacht und es unter Spannung senkrecht an den beiden Fadenenden haltet, sollte es sich nicht bewegen. Wenn man den Faden locker lässt, bewegt sich das Ei langsam nach unten. 

Ein Bild, das Wand enthält. Automatisch generierte Beschreibung

Die physikalische Erklärung für Dummies:

Die Größe der Kraft, die den Faden an den Korken und an die Ränder der Löcher im Ei presst, ist proportional zu der Kraft, mit der die Hände den Faden spannen. Das heißt, je fester man den Faden auseinanderzieht, desto stärker wird der Korken an die Innenseite des Plastikeis gedrückt, die Reibung wird größer und das Ei wird langsamer oder kann sogar zum Stillstand gebracht werden.  

RG≤≤  Fg

RH < Fg 

(RG: Betrag der Gleitreibungskraft; Fg: Betrag der Gewichtskraft des Eis; RH: Betrag der Haftreibungskraft) 

Fotocredit: Alle Fotos wurden von Jana und Pia im WPG Scienceblog selbst erstellt.