Emulsion, oil/ water coloring droplets

Cleaning the fryer back home is not exactly easy. Who usually does this knows that is a messy, sticky and dirty work. To minimize this greasy effect we usually fill the fryer with boiling water and add detergent on a very generous amount. In fact I usually pre wash all the dishes before putting them in the machine. Why? Because it allows the fat to dissolve in the water and not inside the machine or in my hands.

Why?
Because the detergent is an emulsifier, and as such promotes the formation of emulsions.
An emulsion is a system consisting of two immiscible liquid phases (oil and water). We may have emulsions of oil in water (O / W: external aqueous phase) and water in oil (W / O: oily external phase).
The emulsion stability is ensured with use of emulsifying agents such as detergent, surface-active substances generally.

We will need:

• 3 transparent cups, glass or plastic,
• water, enough to fill two cups,
• cooking oil,
• food coloring,
• pencils.

How to:

1. Fill one of the containers with water (2/3) and the other with the same amount of cooking oil;
2. Add 3-5 drops of food coloring to each, leave some space between the drops so that they do not touch each other;
3. What happens?
4. Fill the third container with water up to 2/3, add some oil, enough to form a layer on top of the water.
5. Add the food coloring the same way as in the previous point. Try to predict what will happen;
6. What happens?
7. With the sharp pencil touch a droplet of colorant of the third cup;

What happens?
When the food coloring is added to water, it blends completely with it. When you add the same food coloring to the oil, a small sphere is formed on oil surface.

Why?
Water molecules are polar, in other words they have a small positive charge at one end and a small negative charge at the other, for this reason they remain together, by forming hydrogen bridges. Unlike water molecules, the oil molecules are non-polar - have no charge-, for this reason, the molecules of oil also tend to stick together.

When we "force" an oil to mix with a water based solution (the food coloring) those form an emulsion.
A emulsifier it's a molecule with to different ends, one that loves water (hydrophilic) and a second that hates water (hydrophobic). Imagine a wood stick with two ends, one of them "sinks" in the oil- the hydrophobic end- the other in the water- hydrophilic end. This phenomena is responsible for the formation of small oil droplets -spheres- in the water. This is a stable structure and it's what we call emulsion, many things around us at home are emulsions like mayonnaise and face creams, for example.
If you try to mix the jar 3 emulsion you will verify that after a while the oil will came back to the top..

When you use food coloring (FC), what happens is that the FC droplets drag a small amount of oil with them as a "coat", that's why the FC stop in the oil. the oil acts as a life saver coat, preventing the droplets to drawn. When you punch the droplets with the sharp pencil, the "oil coat" is broken and the FC- a water based solution- blends, almost immediately, with the water bellow the oil. 

Go further
If you want to go further change the variables, one at time and take notes.

• Use different kitchen oil types;
• Use vinegar or any other kitchen liquid instead of FC.

Et voilá!
Now you can avoid your daily bath: "Mom I'm hydrophobic!"

Enjoy!

The air takes space- water in the jar

This is a very simple demonstration that proves the air takes space


We will need:

• 2 jars,
• funnel,demonstração, experiência de física, pressão, propriedades do ar, água,
• water,
• modeling clay, a lot,
• coloring, food coloring is the best,
• pencil, or a pen, a wood stick, something good to punch the clay ...

How to:

1. Fill half of the jar with water;
2. Add a few food coloring to the water, 3 or 4 drops;
3. Place the funnel in the jar;
4. Seal the jar area around the funnel with the modeling clay, the air can't go in or out through the jar/funnel contact zone;
5. Now fill the funnel with some more water.

What happens?
A small quantity of water rolls through the funnel into the flask, but in a few seconds stops, despite the funnel is full of water.

Why?
There is no more space in the jar! The jar is half full of water and half full of air, we must to take the air out in order to get the water get in.

Use the pencil to open a hole in the clay.

What happens?
The water immediately falls into the jar.

Why?
The water "falls" and pushes the air out the jar, now the air can get out through the hole.


Et voilá!
Easy uh?

Enjoy!

Growing crystals at home

What is a crystal?
Crystals are regular structures formed by a regular repeating pattern of atoms or molecules.

These structures grow by a process called nucleation. During nucleation, the atoms or molecules of what we want to transform in a crystal (solute) are dissolved in a solvent. The particles of the solute will tend to cluster together, forming subunits of atoms or molecules. These larger particles will also group with each other and eventually become large enough to "pop out" the solution (crystallize).

Other solute molecules will continue to adhere to the surface of the crystal, causing it to grow until equilibrium is achieved between the solute molecules in the crystal and the solution.

Growing crystals
Three factors that can influence the growth of "home" crystals:

• A good/poor solution saturation- The first stage of home crystal growth is a saturated solute. In a saturated solution the probability of molecules colliding with each other in order to form a core for initiating nucleation is greatly increased.

• Surface type-A rough surface tends to be more attractive for nucleation. It is more likely that a crystal is formed on a piece of rough rope than the in the smooth walls of a glass.

• The presence of deposits in the bottom-This occurs when the solution is not scrambled or means that too much solute was added to saturate the solution. The presence of these deposits create areas for optimum crystal growth however prevents crystal formation in the "target."

Lets see how to grow sugar crystals, these crystals can be sucked and eaten like a lollipop. This demonstration may take up to 3 weeks.


We will need:

• 3 cups of sugar, we have to adjust this quantity, we want to saturated at 100% but no precipitate,
• cup of water, to boil,
• food coloring,
• small jar,
• small bowl,
• wood stick, or rope,
• kitchen paper or paper filter.

How to:

1. Boil the water, careful with burns!;
2. In the bowl, mix the boiling water with the sugar;
3. Stir the water until all the sugar is dissolved;
4. If you want to give sugar some color, now it's the time, add the food coloring;
5. Place this solution in the jar, attention! wash the jar really well to avoid nucleation in it's walls;
6. Avoid any amount of sugar precipitate in the jar- any not dissolved sugar-, this sugar will be a good nucleation "start point";
7. Suspend the stick or rope in the solution, do not wash those, we want this to be a suitable "start up" spot for nucleation;
8. Chose a nice and quiet spot to place your jar for at least 3 weeks;
9. Wait until the solution cool and cover it with a paper filter. 

What happens?  
After cooling the solution will use nucleation spots to form crystals.

NOTE: You must check the jar on daily basis, if you see any nucleation in jar walls, change the jar;

Wait about 3 weeks for excellent results.

Go further:

• Follow the growing crystals with a graph;
• Use salt and compare the growing velocity with the sugar;
• Use 3 jars, in the first one use boiling water, in the second tepid water, and in the last one repeat the essay with cold water;
• Try to dissolve the sugar/salt/other while the water is boiling;
• I am sure you can remember other ways to change this demonstration into a experiment...

 Source: about.com; squidoo.com; buzzle.com
Et Voilá!
Science you can eat!  

Enjoy!

1+1 sometimes is not 2

This is one of the greatest math problems, side by side with the one that states that 0 is different than 0. But this demonstration is not about math, is about Archimedes' Principle.

Archimedes' Principle states:
" a body immersed in a fluid is buoyed up by a force equal to the weight of the displaced fluid"

In other words, when we place a body in a fluid, like water, the volume of the object equals the volume of displaced water.

The simplest example is a bath. If we fill the tub with water up to the top and we lay down inside it, the water will exit, and your bathroom will be a very wet place similar to a lake. The amount of water that came out equals your body volume. You can, with some time and work, calibrate the tub to find out your body volume, 1L=1dm3.
In this example 1+1=2, but sometimes 1+1= "not sure" 

What we need :

• glass container,
• tape, one you can write on
• pen,
• sugar,
• glass container with a scale,
• paper towel,
• straw,
• spoon,
• hot water.

How to:

1. Clean the container;
2. Apply a vertical strip of tape in the container;
3. Fill the scaled container with hot water (container A);
4. Pour the water in the other container (container B); 
5. Use the pen on the tape to mark the water level in container B;
6. Fill the container A again and add the water to the container B
7. Use the pen again and mark the water level in container B;
8. Reject the water;
9. With the paper towel clean and dry container B;
10. Repeat step 3, 4 and 5;
11. Now fill up the container A with sugar;
12. Add the sugar to container B;
13. Use the spoon to mix the solution;
14. Use the pen to mark the level;

What happens?
1 volume of hot water + 1 volume of sugar it's different from 2 volumes of hot water.

Why?
Water molecules are organized like a net. This net is stable and cohesive due to hydrogen bridges. When this net is formed some hydrogen atoms link to neighbor water molecules by a "false" bond with the oxygen, those are called hydrogen bridges. When this happens some "blank spaces" are left between the molecules- in the net. This spaces are as big as the molecules are excited, thats why we used hot water- more empty space makes dissolution more efficient.

When we add the sugar the sugar molecules occupy the empty spaces between water molecules, thats why:

1 sugar unit+ 1 water unit doesn't equal 2 water units

This is a demonstration, but you can make it an experiment:
Go further:
Try with 1 unit of water+ 1 unit of sugar. Does that equals 2 units of sugar?
Try with cold and ice water, what happens?

Et Voilá!
Now you can teach some stuff to your math teacher

Enjoy!

The air takes up space- ballon in a bottle

The challenge is to blow a balloon inside a plastic bottle. A big bottle works better but you can use a small bottle if you want. But is it that easy? Lets see

What we need:

• plastic bottle and stopper,
• latex balloon,
• water,
• nail,
• hammer.

How to:

1. Place the balloon inside the bottle, with the tip out;
2. Try to inflate the balloon, try again!;
3. Remove the balloon;
4. Fill the bottle with water and cap it tight;
5. With the nail punch a hole in the bottle bottom; 
6. Remove the nail and uncap the bottle, what happens?,
7. Leave only a small amount of water in the bottle;
8. Place the balloon inside the bottle again, just like in step 1;
9. Try to inflate the balloon, what happens?;
10. When the balloon is full of air, use your finger to close the nail hole;
11. Stop blow, what happens?;
12. Now remove your finger, what happens?

What happens?
In step 2, you aren't able to inflate the balloon.
When you remove the nail and uncap the bottle- step 6- the water exits the bottle through the hole.
Step 9-  you are successful.
While your finger is in the hole the balloon will remain full of air- Step 11.
If you remove the finger the balloon deflates.

Why?   
Step2- The bottle is full of air, there is no room for anymore air.
when you punch the hole in the bottle the air can escape through it and and "make some space" to the air in the balloon , while you inflate the balloon it "pushes" the air and the water inside the bottle to the outside through the hole.
Same reason explains why the balloon remains inflated in step 11 and deflates in step 12, amazing humm?



Et Voilá!
It takes space

Enjoy!

Newton discs, How do they work?

Sunlight has no color, that's why it is known as white light. In fact the white light is a mix of different colors, these colors are visible only when light passes through a transparent object such as glass, and decomposes in all colors, this effect is commonly called rainbow and scientifically called spectrum.

The spectrum consists of seven colors:

• red; 
• orange; 
• yellow; 
• green; 
• blue; 
• indigo; 
• violet.  

Today we will do a "magic disc"- the Newton disc. We will learn that white light is made by mixing all these 7 colors.

What we need:

• pencil,
• scissors,
• thick white card,
• crayons, markers will do,
• ruler,
• compass,
• protractor.

How to:

1. Cut the card in a circle, use a compass;
2. Use the protractor to divide it into 7 parts, like in the picture, sections of 55 º, 60 º and 35 º;
3. Paint each piece with a spectrum of colors, the figure shows the red, the orange, the yellow, the green, the blue, the indigo and the violet. Paint it as uniformly as possible and use the same intensity with all the colors;
4. Make a hole in the middle of the circle and pass the pencil through it, the center of the circle is where the "hole" of the compass is;
5. Spin the pencil quickly, like a top, look at the color wheel, adjust as necessary to rotate the set easily.

What happens?
The disc appears as a grayish white tone.

Why?
In fact if the conditions were optimized we would see a clean white circle, without the grayish tone.

The colors painted on the wheel are the main colors of the white light, like those that are present in the rainbow. When the wheel spins it creates a visual effect that makes your brain believe that they mingle and wheel appears white when in reality it´s multicolored.

This is a demonstration, turn the test in to an experiment, experiment with different color combinations. Here are two suggestions: red, blue and green, or red and green for example, what happens? Why?

Et Voila!
After all the white has a lot of color

Enjoy it!

Floating pin

Another demonstration. So simple but so interesting

What we need:

• straight pins,
• water,
• toilet paper,
• bowl.

How to:

1. Fill the bowl with water;
2. Wait a few seconds until the water stop moving;
3. Can you place a straight pin floating in the water? Try it;
4. What happened?
5. Try a second pin.
6. Place the pin on the top of  a piece of toilet paper;
7. Place both things in the water, very carefully and gently
8. Wait a few seconds.

What happens?
The paper sinks, the straight pint floats.

Why? 

Surface tension, that's the answer.

When we place the pin in the water, without using the paper, it immediately sinks, its weight is too high for the area it occupies, ie is very dense.

The paper, by contrast have much area for the weight, in fact it doesn't sink, actually it soaks, in other words water molecules fill the paper pores in it's porous structure and fill the voids in the web cellulose paper. this way the paper becomes heavier and sinks.

Surface tension is responsible for what one might call "skin."

The water surface is formed by a barrier of water molecules. This barrier is what allows insects to land on water, the soap bubbles to exist, and the pin does not sink.


The first pin sinks because it doesn't start from a position of equilibrium and rest, unlike the second which is resting on the paper. The paper when sinks exerts sufficient force on the skin of the water to bend it but not to break it, and the pin floats.

Et voilá!
It's magic! No, it's science!

Enjoy!

Electric and bouncy pepper

This is another version of the Jumping paper circles demonstration.
Today we will use black pepper powder.
 
What we need:

• black pepper powder,
• salt, 
• wool cloth,
• plastic fork or spoon,
• plate.

How to:

1. Mix some pepper and salt in the plate,
2. Mix well, use the fork to help you;
3. Ask your restless to separate the salt from the pepper, humm... tricky uh?;
4. Rub the fork in the cloth for 30-60sec;
5. Approach the fork and the plate, keep the fork 2,5cm away from the plate.

What happens?
The pepper jumps to the fork, leaving salt behind 

Why?
When you rub the fork with the cloth it becomes negatively charged, pepper is positively charged. That means, when you approach the fork the pepper is attracted to it, and "jumps".
The salt is also negatively charged but is slightly heavier and it doesn't jump so easily. However, if you don't keep fork distance the salt will eventually jumps, thats because the electrical attraction overcomes the weight.

See the movie:

You can learn more about this here.

Et voilá!
Bouncy pepper!

Enjoy!

Jumping paper circles

This is a classic! A electric balloon full of static electricity
What we need:

• 1 balloon,
• 1 wool cloth, you can use your hair,
• 1 paper hole puncher,
• old paper, reuse some old paper.

How to:

1. Blow the balloon;
2. Punch some holes in the paper, fold the paper several times before you use the puncher, that will give you more circles;
3. Rub the balloon in your hair or in the cloth;
4. Approach the balloon and the paper circles.

What happens?
The circles "jump and glue" to the balloon walls.

Why?


Although this is a very simple and basic demonstration some of us never stop to think about what is really going on.
The paper and the balloon are made of atoms. This atoms have a positive core surrounded by negative electrons, these move around the core.
As we saw here several times everything tends towards an equilibrium and thats why almost everything that surround us is charged with a neutral charge. Is the same as saying that the sum of its charges is 0.


Repulsion and/or attraction are only possible if the charges of both materials are different in sign. That means: repulsion and/or attraction are only possible when the objects have excess or lack of electrons and because of that have a negative or positive charge.

When the balloon was rubbed it passed from a resting state to a excited state, and therefore electrically charged(in this case with excess negative charge).

Why the balloon become charged? This was possible because the cloth and the balloon have different characteristics, one can receive electrons and the other can give them, despite they are both in a rest state to begin with. This means one is electronegative (easier to receive negative charges, balloon), and the other is electro-positive (easier to donate negative charge, hair or cloth), when two such materials are rubbed, negative charges migrate from one material to another, when are removed one is positively charged and the other negatively. If you use the hair you will find that it "will glue to the balloon."

The paper was in a rest state, neutral charged. If that is true why does it jumps to the balloon wall?

Yes, the paper was not charged.

The attraction between a neutral charged material and another can be explained using the idea of electrical dipoles, a phenomenon commonly referred to as "charge separation" (in Figure). This separation happens when neutral object is subjected to the action of other electrical charges, in this case electrical charges of the balloon, thats why the paper circles "jump" to the balloon, attracted by the negative charges.

Note: This electrical phenomenon only occurs between insulating materials, conductive materials do not have the ability to retain electric charges, as they seep through the material.

A step further:

• Change the rubbing time;
• Change the friction material (cloths can try silk, cotton, wool ...);
• Change the amount of air in the balloon.
• Make a table to record your results.

ATTENTION:
Do not forget the first rule: do not change more than one variable at a time.

sources: cienciamao.usp.br; eurekahandsonmindsonscience.blogspot.com

Et Voilá!
So simple so scientific

Enjoy!

Floating lemmons, or not

Observation:
Peeled lemons sink, unpeeled lemons float.

Why is that? Maybe the lemon peel acts like a lifebuoy, keeping the lemon above the water line.  

What we need:

• water,
• small box or a glass container, transparent,
• 1 lemon,
• your lab notebook.

 How to:

1. Fill the container with water, enough to float lemon;
2. Place the lemon inside the container;
3. Observe carefully what happens and record the results in your notebook;
4. Remove the lemon from the water;
5. Peel the lemon;
6. Place it again on the water;
7. Observe carefully what happens and record the results in your notebook.

Attention: Ask an adult o handle the knife

 

What happens?
Peeled lemon sink, unpeeled lemon float.

Why?
Notice that when the lemon was unpeeled it only sunk enough to stabilize its weight. In the picture you can see 1/4 of the lemon off water.

This is due to, at least, two factors, density and porosity.

Density, density depends on lemon weight and volume. But if we peel the lemon it becomes lighter nevertheless it sinks.

Porosity, Lemon peel is extremely porous and when placed in water, the air is trapped in these pores and can not escape, this makes the lemon float. Just enough to compensate its weight.

By simple observation we can see that the peel is made off two areas, a white and spongy one and a yellow and porous one. What if we separate this yellow and white areas?

1. Place the lemon peel in the water. Does it float?
2. Observe carefully what happens and record the results in your notebook;
3. With a knife separate the yellow section from the white section;
4. Try to place the white section in the container. Does it float?;
5. Observe carefully what happens and record the results in your notebook;
6. Now try with the yellow exterior section;
7. Observe carefully what happens and record the results in your notebook.

"The peel white section" floats! The yellow one sinks!
If you look closer you can see that the white section is very spongy, and therefore very light, ie works as a buoy.

In terms of evolution, in which only the fittest survive, we see this floating lemon as a competitive advantage, the fruits may fall from the tree, float in a water course and travel to other destinations and lands where their seeds can proliferate at will.


A step further:

• Use different citrus, like lime or orange.
• Use different fruits like  apples or bananas.
• In nature we can find different thicknesses of peels in lemons. Do the peel thickness affect the outcome?

Et voilá!
Archimedes in action.

Enjoy!

Bernoulli demonstration- Blow the ping pong ball

Use a hair dryer and a simple ping pong ball and you can make a simple but great Bernoulli Principle demonstration- check it out here.
Today we will see the same Bernoulli Principle working in a different way


What we need:

• ping pong ball,
• plastic soda bottle, funnel,
• scissors.

How to:

1. Cut the top of the bottle, the rounded section, just like shown in picture;
2. Place the ping pong inside;
3. Fill your lungs with air;
4. Blow in the bottleneck, as many times as you want.

What happens?
Nothing! The ball stays in the plastic bottle section.

Why? 
The air you introduce in the plastic "cup" make its way leaning against the walls of the ball, as shown in the picture, causing it to rotate instead of rising.

Of course it is possible to make the ball "fly" but no lungs are able to do it.

See the video:

Et voilá!
Your Lungs can't do it!
Enjoy!

It's magic? No it's Science

With water, and a cardboard you can do a little magic with your restless.
This water is defying gravity.
Thats because the air in it can't escape to let in new air.

Et voilá!

It looks like magic, it sounds like magic, it tastes like magic, but it's science!

Enjoy!

Overcome the force of gravity

When we add salt to water we increase its density, which will allow some objects to float.

What we need:

• 6 glass jars,
• different objects, like beans, grains, paper clips, eggs, etc.. we used dry beans, dry grain and an olive;
• salt,
• dessert spoon,
• water,
• pen,
• labels,
• your notepad.

How to:

1. Clean the jars;
2. Label them with letters or numbers;
3. Select the objects you want o test,
4. Write on your notepad which letter goes with each object, one of the jars will be the control, for example A- control; B- olive; C- bean....;
5. Fill the jars with the same quantity of water, we used 250ml;
6. Verify if any of your objects floats;
7. Write down your results;
8. Take the objects from the jar;
9. Add 1 dessert spoon of salt to the B jar, 2 to the C, 3 to the D... don't add any salt to the first jar (control);
10. Mix it well until the salt is all diluted, if you are using jars with lid is easier to close the jar and shake;
11. Test all the objects, one by one, jar by jar;
12. Write down your results.

At the end you will have precise notes about the number of spoons you need to add to water in order to float  a certain object.

These were our results:

A- 0 salt
B- 1 salt
C- 2 salt
D- 3 salt- floats: grain
E- 4 salt- floats: red bean; black bean
F- 5 salt- floats: white bean; olive

Attention: you may get different results; those depend on the beans/grain/olive trademark, size and water content.

It's possible to find on internet and some books some references to some restless minds that made heavier objects to float, like marbles, or stones, using larger amounts of salt. We didn't test those objects, in theory, yes it's possible to make it happen, but the amount of salt in the water will be hugely high.
Accept this challenge and try to float denser objects.

What happens?
As you salt the water, this will become denser, in other words, heavier. This density is closely linked to the force that water exerts on the items, if this force is higher then the force that pushes objects down (gravity) the objects are boost up and float.
With this experiment you can also observe water saturation, write down the number of salt spoons you need to saturate the water.

It is possible to do some variations to this essay:

• Use only one kind of bean but with different water levels (1 dry, hydrated but raw and 1 cooked);
• Use only one kind of bean with different water levels, from 3 different trademarks (dry, hydrated, cooked from trademark A, dry, hydrated, cooked from trademark B; dry, hydrated, cooked from trademark C);
• Use green olives or black, with pit, without pit...

Write down your results.

Et voilá!
Can you make it work with the marble?

Enjoy!

Swirling colors in a milk bowl

Try this and watch the colors swirl in a milk bowl. This is very easy to do and takes less then a minute to do.

We need:

• bowl,
• food coloring, red and blue,
• toothpicks,
• detergent,
• milk.

How to:

1. Pour a bit of milk on the bowl;
2. Add 2 drops of blue food coloring;
3. Now, away from the blue, add another 2 drops of red food coloring;
4. Let your restless play with the toothpicks and the milk on the bowl, let them "draw" at will, What happens?
5. Now, add a drop of detergent;

What happens?
The colors blend immediately, almost instantly, after we add the detergent

Why?
When we add the food coloring, it just stay there, exactly where we placed it.
Then, when we introduce the detergent to the equation, the colors blend in a sec. That’s because the detergent will make the surface tension to drop, and the "milk skin", that allows the color "to sit there", will disappear.
As we saw  here, this skin works as a coat that maintains other molecules at surface, and therefore preventing its dissolution n the milk. When his surface tension is disturbed, the food coloring (and other milk molecules) find less resistance and therefore they can move all around in the bowl.
But there is another phenomena happening in the bowl: Some milk protein denaturate by the action of detergent.
Both things contribute for the surface tension changes.

See the video:

Et voilá!
A ocean of colors!

Enjoy!

Coanda effect

Try this:

We need:

• a candle,
• a bottle,
• match box, or any other small rectangular box.

How to:

1. Light the candle;
2. Place the bottle between you and the candle, close as possible but without touching each other
3. Place yourself near the on the opposite side and blow to the bottle, like you wish to extinguish the candle, what happens?;
4. Light the candle again;
5. Replace the bottle for the box;
6. Now blow, try to blow with same intensity.

What happens?
When you e a bottle the candle extinguish at first blow. When you use the box, the candle resist, even if you blow harder.
Eventually it will extinguish if we blow very hard, that’s because a vortex will be formed and the air circulation will extinguish the candle at the end.

Why?
This is a simple Coanda effect demonstration.
Coanda effect was discovered in 1910 by the Romanian engineer Henri Coanda (1885-1972), Coanda began to study this phenomenon after having he crashed a prototype aircraft (Coandă-1910). (1)
To the capacity of a fluid, to follow on a curve surface, like it's glued to it, we call Coanda effect- of course this is a very simple way to explain this, in fact is far more complex.

Bottle surface is smooth and curved, and the air we blow travels like its glued to the glass surface, the air goes around the bottle circumference, this allow us to blow the candle with just a little breath. On the other hand, the match box is a rectangular and plain surface, in this case the air flows to the corner of the box, this corner is a 90º angle, and therefore the air can't travel glued to the surface, like in first example. In fact the air is expelled away from the candle; this will form a vortex, which will eventually extinguish the candle.
This effect helps to explain why the plains stay in the air. 

Et voilá!
Simple and fun!

Enjoy!
Sources:
in pt.wikipedia.org/wiki/Efeito_Coand%C4%83