Send us your questions

Some of our visitors have sent emails with interesting questions, we decided to start having a space to answer them. In this space the blog "Restless Minds" will answer all questions you send us
Send us your question for the email: Restless Minds.

Science progress affects our daily life and "to know" means you are going to chose right, because it allows you to form your own opinion on scientific everyday issues. On the other hand, having an elegant and harmonious vision of the world where we live in leads to a feeling of intellectual satisfaction.
We believe this kind of scientific day to day knowledge should be encouraged from an early age, and that's why this project was born: science, culture, knowledge, crafts for your restless mind.

Tuesday, November 29, 2011

Christmas tree string ornaments

Another cool idea to make your Christmas tree the coolest in the neighborhood.

What we need:
  • balloons, we only blow it half way, chose the right size;
  • string, any color;
  • scissors,
  • ruler,
  • white glue,
  • water,
  • brush,
  • glitter
  • small bowl,
  • tablespoon,
  • tissue painting,
  • smmal sponge,
  • old newspaper,
  • plastic cup,
How to:
  1. Cover the work table with the old newspaper sheet;
  2. Cut a piece of string with 10 cm;
  3. Blow the balloon until its circumference is 10cm, simply place the 10 cm string around the balloon, when the ends touch each other the ballon has a 10cm  circumference;
  4. If you want to make several ornaments this 10cm don't need t be exact.
  5. In the small bowl mix the glue (3 tablespoons) with water (1 tablespoon);
  6. Cut a piece of string with about 6,5ft;
  7. If you want to paint the string, now it's the time, place a bit of fabric paint in a small sponge, grab the string with the sponge, next drag the sponge along the string to paint it;
  8. Let it dry for 3 or 4 hours;
  9. Dip the string in the glue, until it is soaked;
  10. Grab the balloon with one hand, and with the other one wrap the balloon with the string, your hands will be full of glue, don't worry water will take care of it later;
  11. When you finish press the string end against the balloon;
  12. Let it dry for 24h on the top of the plastic cup;
  13. In the next day blow up the balloon, and pull it through the holes in the string, cut it in small pieces if you need, don't cut the strings!!!!!;
  14. Glue all the ball again;
  15. Apply glitter;
  16. Hang on Christmas tree!
If you don't have glitter you can reuse old Christmas ribbons. Just cut the ends into small pieces. It's not the same thing but it works.

Et Voilá!
Another Christmas idea!


Bending bones with vinegar, the rubber bone

We can have lots of fun with vinegar. We leave you with another demonstration with this stinky friend.
Bending bones
What? Bending bones? How?

Yes, bending bones, the effect works best if we use a bird bone, that’s because this bones are hallow.

What we need:

  • a jar, with lid, big enough to the bone,
  • 1 chicken bone, Lucky bone or the leg bone works best,
  • Vinegar, no flavors, no additions.
How to:
  1. Wash the bone, with running water;
  2. Show the bone to your restless, show him/her how hard is to bend it;
  3. Place the bone on the jar;
  4. Cover it with vinegar;
  5. Screw the bottle cap;
  6. Let it rest for 3 days, place the jar in a safe place, you don’t want your kitchen smelling like vinegar;
  7. Remove the bone;
  8. Wash it on running water;
Bend it, tcham tcham! Is it really a rubber bone? Well it looks like one

Like our bones, chicken bone have calcium, this mineral gives it hardness.
What does the vinegar do to make this happen?
Vinegar is a weak acid, but it's strong enough to dissolve the bone calcium. Once the calcium gone there is nothing more to make it hard- all that remains is the soft bone tissue. Just like what happened here with the naked egg.

Ask your restless to answer this questions:
  • Does the number of hours the bone is in the vinegar affects the final outcome? How?
  • Does the size of the bone affect the demonstration? How?
  • Using different kinds of vinegar will lead to different results?

Et voilá!
A rubber bone


Painting old CD's

We found this Tutorial here it’s a very good idea to reuse old CD's and DVD's rather than throw them in the trash and besides, this will keep children occupied for a while

What we need:

  • Paint tutorial says it can be acrylic or nail polish. Use synthetic lacquer for longstanding results,
  • CDs and/or DVD's old and broken,
  • Varnish.
How to:
  1. If you want to leave your CD or DVD transparent, sand it, with thin sand paper, when you done wash it and dry it well;
  2. If you want to keep the "mirror" effect just clean it with alcohol to remove any grass and dust. You can apply paint on the "label" side;
  3. Let your restless paint the CD/DVD;
  4. Wait at least 24h before you varnish it.
You can paint geometric figures or use a stencil.

This CD/DVD's can be used for a lot of things. We can place them in the wall, one by one or as a set, we can frame them, or build some, dream catchers...

Et voilá!
Young restless will love to explore this circular canvas.


The air takes space- Try this

Another simple and basic science demonstration. Restless Minds already played with air a few times, check it out.

What we need:
  • flask with lid, metallic works best,
  • nail,
  • hammer,
  • straw,
  • molding clay,
  • water.
How to do it:
  1. Use the nail, and with the hammer punch a hole on the lid big enough for the straw. Don't let your child use the hammer;
  2. Fill the flask with water to 2/3, you can use juice;
  3. Close the flask with the lid;
  4. Place the straw in the hole;
  5. Seal the hole with the clay;
  6. Drink it, using the straw.
You can't drink. At beginning this looked a bit stupid right? But now you understand.

When we use the straw we don’t really think about what happens in the plastic tube, but the straw only works because the liquid we suck is replaced with air. In fact is all about pressure.
  • When, in optimal conditions, we place a straw in a drink, the air pressure in the drink in exactly the same inside the liquid on the straw.
  • When we pull the liquid up, we remove some air from inside the straw, and the pressure inside the plastic tube drops.
  • While this is happening inside the straw the pressure on the surface of the liquid remains the same.
  • This pressure variation, between surface and straw interior, makes the liquid to be pushed through the tube.
  • If we close the flask, and prevent the air from circulating freely there is no way to create a pressure differential and therefore there isn't nothing to push the liquid into the straw!

Et voilá!
The juice will stay there, until you unseal the jar!


Instant facts- Just add water 7

World Population:
is currently growing at a rate of around 1.15 % per year.
growth rate reached its peak in the late 1960s, when it was at 2%.

Monday, November 28, 2011

Needle magic trick

We saw here several demonstrations that give incredible magic shows. It'e a fact the balloon trick is an oldie, but is also true that sometimes the simple is the most interesting.

Before anything else: When does a balloon bursts? When the air inside is suddenly expelled, otherwise the balloon doesn't burst, just empties.
We say it bursts because it makes a big BOOM!
What we need:

  • balloon,
  • sewing pins ,
  • strong tape,
How to:
  1. Fill the balloon half way;
  2. Glue small pieces of tape, 2, 3 ,4 ... as you wish, it will depends on the number of pins you have and on balloon size;
  3. Make sure that the tape is well glued to the balloon, air bubbles will lead to a big BOOM!;
  4. Gently, but without fear, stuck a pin in the center of duct tape;
  5. Repeat this to all pieces of tape in the balloon.

What happens?
Balloon doesn't burst!

The balloon burst when the air is suddenly forced out the rubber coat. In this demonstration it doesn't burst because we made a "seal"- with the tape- around the spot where we pin it, here the rubber is reinforced.

We can try to take the pins of the balloon, which will make the balloon emptying slowly. While the tape
resist the balloon will not burst.

Try to observe the rubber ripping beneath the tape, near the spot where you place the pin, when the air pressure, inside the balloon, overcome the tape "seal" we can observe a small tear underneath the  tape.  The more the balloon is filled, the greater the pressure is, and faster the pressure overcomes adhesive and tear appears, the next step is Bang!

  • Glue the tape pieces apart from each other;
  • Use light color balloons, it will be easier to observe;
  • Use strong tape, works best
You can try to understand better this pin magic:
  • Use several balloons, same sized; fill them with different air quantities. Use a chronometer and see how long the air pressure takes to beat the rubber "seal". 
    • What is the ideal volume air?
  • Use more then 1 pin, and on each balloon vary the space between the tape pieces. 
    • Does this have any influence on the time the balloon takes to lose the air? 
    • And does it simply lose all the air or does it burst?

Et voilá!
It's magic


Dye techniques for T-shirts

Dye a T-shirt with the desired pattern, or at least a minimally predictable pattern, it is not a random challenge, today we share with you some techniques you can use, you can check the information on dying techniques here: Stamp and dye t-shirts, summer DIY.

Make sure the rubber bands are tight!

Knot technique
  • Grab the T-shirt on both ends and twist it, like a rope,
  • Tie a knot in the fabric. 
  • Place the T-shirt in a plain surface.
  • Place your thumb on the fabric; exactly in the place you want the spiral central.
  • Use your fingers to secure the fabric in place, and start to twist.
  • After each twist, with your free hand, flatten the fabric to prevent the spiral to fall apart.
  • At the end of the twists you must have something that looks like a giant flattened biscuit;
  • Put the rubber bands in place, like the picture.
  • This effect creates a pattern of overlapping or close circles;
  • Use a pencil to mark on the t-shirt a few points, these points will be the center of the dyed circles;
  • Use the thumb and forefinger to pick up the fabric in the same place you painted the point;
  • Hold this "tab" with the other hand;
  • Repeat the process for all the dots;
  • When finished you must have several of this "tabs" in your hand.
  • Wrap a rubber band around each "tab", and wrap 2 or 3 around all the set.
  • Wrap the t-shirt forming a long tube. The lists will be dyed perpendicular to the tube.
  • Squeeze the tube with the rubber bands, the more the bands are spaced thicker will be the lists.

Source: this idea came from here

Et Voilá!
Exclusive T-Shirts! 
Lean how to dye


Hunting animals with a camera

fotografar animaisThe child must understand there is live everywhere, under the stones, near the pool, on the sand under our feet...

What we need:
  • a camera, preferably cheap, the child can broke it, it can be a cell phone or disposable, for example,
  • a computer, for downloading photos,fotografar animais
  • a notebook,
  • a pen.
The project is simple but requires some hard work:  

    fotografar animais
  1. Stimulate your child to find a spot with live. Let him/her to take the camera everywhere he goes. Let him to look, to find and to capture the moment with it;
  2. Its allowed to capture same species in different locations;
  3. Tell him to take note of the place, time of the day, and other important information when shooting, for example, "Park, 2:30PM, very hot, 5 animals photographed in the grass, 2 near the swing";
  4. Download photographs to your computer;
  5. Place them is a special folder, named it after the place and/or the day where your child took the photos, your restless can do this, on the notebook write down the name of the folder corresponding to the location described previously;
  6. Let your restless child name each photo with the animal real name. Let him look for the names he doesn't know on the internet and/or books…;
  7. To finish you can place all the pictures on a slide show, he will be amazed with all the animals he saw.
fotografar animaisThe duration of this project is variable, only parents and/or educators can evaluate the availability of children for this project.
Set a day, or a specific hour during the day to catalogue and download the photos, or, and trust me on this one, it will be the chaos.

fotografar animais
Explain to the child that in any case he/she should arm the animals he/she is shooting, tell him/her not to hold them in his/her hands... any of this actions can lead to the animal dead or trigger defensive reactions.

If the child prefer use the vegetable kingdom

Et Voilá!
Life is everywhere waiting to be found!


The shrinking bottle

We already did several demonstrations here to prove that the air takes up space.
Today the demonstration is another way to play with the air.

What we need:
  • plastic bottle, with cap,
  • hot water,
  • funnel.
How to:
  1. Wash the bottle;
  2. Let it dry;
  3. Heat up the water, don’t let it boil, its not necessary;
  4. With the funnel pour the water in the bottle;
  5. Wait for 10 sec;
  6. Reject the water to the sink;
  7. Quickly cap the bottle again, you have to be fast.
What happen?
The bottle shrinks.
In other words, the bottle walls collapse.

Remember this? What happens to the bottle is exactly the same thing.
Before further explanations is very important to understand two things:
First: air exerts pressure on the bottle, like in everything around us, including ourselves.
Second: any forces system tends to look for equilibrium.

The hot water heats the air inside the bottle. Try to close the bottle immediately after pour the water inside, the bottle will swell, that’s because hot air can't escape to atmosphere. When you reject the water, the air inside the bottle rapidly cool. The cool air occupies less space then the hot air, and, theoretically there will be a lot of "empty space" inside the bottle, because of that the plastic walls collapse under the pressure of the air outside the bottle.

Et voilá!
Another fun way to spend some time


How to do a parachute toy

This is a old toy, no batteries needed, no updates or upgrades, just the plastic soldier and the plastic bag. Today we are going to see how to build a parachute and how it works.

We will need:
  • plastic square with a 40cm (about 15in) side. You can use a garbage plastic bag,
  • Scissors,
  • Ruler,
  • Pen,
  • 8 strings with 30cm (12in) length,
  • A small toy, like a plastic soldier.
How to:
  1. On each side of square measure and mark, with a pen, 4, 8 and 12in, like the image bellow;
  2. Cut off the shaded parts;
  3. With the scissors punch a hole on each corner of the plastic, like the picture, holes must be small, large holes will compromise the parachute;
  4. Attach one string to each punch you made, with a knot;
  5. Attach the other string end to the toy; the toy must have no more then 10cm (4in) height.

  6. Figure1
  7. Throw the parachute from a height place, like a balcony; remember the goal is to land the toy gently.
We hope your parachute landed gently giving an opportunity to your toy to survive.
When you throw the parachute the toy (the weight) pulls down the strings, forcing the plastic to open. Now the parachute contact surface with the air is bigger, the air resistance is also bigger and that’s why the parachute goes down slowly. The greater the air resistance the smoothly the parachute falls.

Try this with your restless:

  • Throw the parachute from different heights, keep a record of your results and variables:
    • Compare the falling times,
    • The parachute always opens?
  • Cut a small hole on center of the plastic, this will help the air to escape:
    • Does it fall faster with or without the hole?
Et Voilá!
A plastic soldier parachute


Giant soap bubbles

Blowing Bubbles

Dip your pipe and gently blow.
Watch the tiny bubble grow
Big and bigger, round and fat,
Rainbow-colored, and then

Margaret Hillert

Yes, today we are going to play with giant soap bubbles.
Not much to say about them, just that they make children smile and adults dream ... give a child a bubble, and its like you are giving her/him the magic itself.

What we need:

  • 2 cups of washing dish detergent,
  • 3 cups of warm water,
  • four ounces of glycerine, buy it at the drugstore, the secret ingredient,
  • large bucket, preferably with a lid,
  • "Hula Hoop",
  • small stool,
  • rubber pool, the hula hoop must fit
How to:
  1. Mix all ingredients in the bucket, water, detergent and glycerine;
  2. Upon mixing the solution pour it in the pool;
  3. Put the bow in the pool;
  4. Place the stool inside it;
  5. Equip your restless with goggles, fins, swimming suit, and whatever else you can remember of;
  6. Lift the Hula Hoop in order to cover the child, he will found himself inside a giant soap bubble!;
  7. Now, let your restless try it, replace him/her in the pool.
For better results:
The weather must be warm, wet weather works best
Heavy water makes this demonstration more difficult

But what happen in a soap bubble?

Surface tension
H2O molecules are in red and white
Blue circle:
hydrophilic end of the soap molecule,
Black "tail":
hydrophobic end of sap molecule
The soap is the main ingredient on a soap bubble; moreover, if you want to try, brands and different types of dishwasher detergent give different results. Soap is made of molecules with two distinct ends, one hydrophilic and another one hydrophobic. The first one attracts the water, the second repels it.
If we could cut a bubble we would see something like the picture, a water layer surrounded by two soap layers, one inside the other outside the bubble.
The interaction between the soap bubbles pushes the water molecules away from each other relieving surface tension.
On the other hand glycerine bonds with hydrogen in water preventing evaporation.

But a question remains:
With the hula hoop we can make spherical giant soap bubbles, but if we use a square form can we make square bubbles?...

Because everything in Nature happens with the minimum possible energy spent. This is a basic fact of Nature.
Surface tension of the bubble "is going to shape" it in a form with the less possible area to contain that volume. That shape is the sphere- also called bubble- the most effective shape in universe when comes to energy saving. Look the Sun, the planets, the water drops, the berries, and I am sure you can remember a few more spheres

Et Voilá!
Who would say we can learn with sop bubbles?


Making a shower- air pressure

Today we are going to see something we see every day but we are not trained to think about it. In fact is very simple and very easy to understand.

When we uncap a bottle and we turn i upside down, the liquid inside is spilled. But it will go slowly if you maintain the botlle at the 90 degrees angle, if you reduce the angle to 45 or even 30 degrees the flow of liquid increases . 

If it's your job to refill the cruet you know exactly what we are talking about.

What we need 

  • plastic bottle,
  • water,
  • hammer.
  • nail,
  • big bowl.
How to:
  1. Fill the bowl with water;
  2. With the hammer and the nail open 3 small holes on the bottom of the bottle, don't make them to large;
  3. Place the bottle inside de bowl;
  4. Fill the bottle with water;
  5. Close it tight;
  6. Grab the bottle by its neck and lift it, don't squeeze;
What happen? 
Nothing, water remains inside.
Slightly uncap the bottle, and now?
Close it again, and now?
We easily observe that even with a punched bottle the water stays inside, however, if we uncap the bottle the water flows.

The bottle is filled with water, but in order to make the water come out the bottle it is necessary that something "takes its place" inside the bottle.

Since the bottle is closed and the bottleneck is the only place where "something" can go in the bottle, the water stays in.
This something is the air. When we slight uncap the bottle the air goes in and push the water down, through the holes, taking its space inside the bottle.

In other words:
Atmospheric pressure.

When the cap is tight, the atmospheric pressure, which acts in all directions, apply force through the holes and secure the water inside the bottle.
If the bottle is closed, that pressure doesn’t act directly on the surface of water, the water remains inside.
If you uncap the bottle, atmospheric pressure acts in water surface and the water falls through the holes.

Et voilá!
Tricky uh?


Instant facts- Just add water 6

Humanity's right-hand dominance might be more than 500,000 years old.

Friday, November 25, 2011

Instant facts- Just add water 5

Children laugh about 400 times a day, while adults laugh on average only 15 times a day.

Thursday, November 24, 2011

Instant facts- Just add water 4

A typical pencil can draw a line 35 miles long or write about 45,000 words.

Wednesday, November 23, 2011

Osmosis demonstration using eggs

Remember this? Today we are going t need 2 of those, maybe more if you want to go a little further.
Today we are going to play and learn about osmosis.

Before continuing:
Cells have several transport mechanisms, in other words, several different ways to make the molecules to pass from inside to outside and vice versa. On of those mechanisms is called osmosis, and we can say for sure "that's all about concentration".

Osmosis is the movement of solvent molecules through a membrane from a region of  lower solute  concentration, to a region of higher concentration.
In other words, and considering the solvent is water, osmosis is the movement of water molecules from "in" or "out" the cell, aiming to match the concentration on both sides of the membrane.

In general we only can see a cell with a microscope. You don’t need a super microscope like electronic, a optical is enough.

In Nature there is a group of cells witch don't need a microscope to be "seen”, the eggs of species that "lay eggs." Ostrich eggs are the biggest eggs (not extinct specie), humming birds are the smallest, to "make" one ostrich egg we need 24 chicken eggs.

The egg is a cell, full of potential, to become a new being; only our frying pan or a starving predator can stop it from happen.
This cell have, like any other cell, a membrane (works as envelope for white and yolk), this membrane is double layered and is easy to observe on the blunt region where it forms a air pouch.

Let's start our demonstration. Before anything else we need to "undress" 2 eggs, you can see how here.

Let’s go

What we need
  • 2 jars with lid, big enough to place the egg inside,
  • marker, to write on glass,
  • water,
  • 2 naked eggs,
  • honey.
How to:
  1. Put a "naked egg" in each jar;
  2. Fill the first with water;
  3. Fill the second with honey;
  4. Close the two jars;
  5. Label them with the marker, write on the first "H2O" or "water" and in the second "honey";
  6. Place the jars in the refrigerator;
  7. Wait 24 hours;
  8. Take the eggs of the jars.
  9. What do you see?
The egg in the water jar looks like swollen and smooth.
The egg in the honey jar looks like wrinkled.

The white part of the egg has 90% water and the honey has only about 18%. We placed our cell (the egg) in two different environments, the water (with 100% water molecules, or close enough) and the honey (with about 18% H2O).

In the first case the water flow goes from a 100% environment to a 90% environment, from the water to the cell (egg), theoretically until the two concentrations are set at 95%, the egg swells.
In the second jar the water flows from the 90% environment to the 18% environment, from the cell to the water, theoretically until the two concentrations are set at 54%, the egg wrinkles.

At this process, where solvent molecules move (in this example H2O) to find a equilibrium concentration, in two different environments, separated by a membrane, we call osmosis.

  • |X| here the outside H2O concentration match the inside concentration;
  • |>X| here the concentration outside the cell/egg membrane is lower then the concentration inside it, the honey example.
  • |<X| here the concentration outside the cell/egg membrane is higher then the concentration inside it, the water flask example;
Make this an experiment
Try other variables; remember to write down all your observations:
  • Use water with food coloring;
  • Use alcohol;
  • Use salt water;
  • Use Vinegar;
  • Or simply, place your "honey naked egg" in a jar with water and wait another 24h, what do you think it will happen?

Et voilá!
Play with eggs, learn from them


Instant facts- Just add water 3

The major ingredient in ice cream is air
in ""

Tuesday, November 22, 2011

Black hole magic

Today we are going to do some magic!
Your restless will be amazed!

What we need:
  • chose a easy cleaning surface, as always, to avoid problems,
  • rubber gloves,
  • metal can, any size will do
  • Styrofoam, like the ones in the images.

How to:
  1. Put your gloves on;
  2. Make a large pile of Styrofoam;
  3. Pour the acetone in the can, about 1 in high;
  4. Ask your restless to set aside the quantity of Styrofoam he/she thinks to fill the can;
  5. Drop the pieces into the can one by one;
  6. Keep dropping;
  7. The pile is finish? Grab some Styrofoam from the big pile and keep dropping;
  8. If everything goes as planed the big pile will disappear before your eyes into the can, like it was a "black hole" that grabs everything around it.
Styrofoam vanish in the can!

The actors:
The acetone is an organic compound (CH3)2CO, is a highly flammable liquid with a high level of solvency. A lot of compounds dissolve on acetone, like nail polish.
Styrofoam is made of polystyrene. Manufactures use a blown agent that helps to transform the polystyrene in Styrofoam, the product this procedure originate is a highly porous and rigid polymer, with high percentage of air, trapped on porous

What happened?
In fact what happen is very easy to explain. Styrofoam is a polymer, made of several chemical units linked (like all polymers), acetone works on this links breaking them. Once the Styrofoam is made by thousands of air bubbles, all that remains at the end of the chemical reaction is: air.
Styrofoam is a very light material and with a lot of air inside, that makes it perfect o disappear with a small quantity of acetone.

After all where did the Styrofoam go?
When Styrofoam dissolves in acetone it doesn't disappear. Don’t forget  the statement "In nature, nothing is created, nothing is destroyed, everything is transformed". Polystyrene molecules continue in solution. Styrofoam solubility is very important when comes to recycling. Polystyrene in acetone solution can be extracted and used to make new materials avoiding its accumulation in sanitary landfills.

Kids must be kept away from acetone,
Use other acetone then the nail polish remover for better results.
Verify if what you are using is really Styrofoam and isn't other similar biodegradable product

Et voilá!
It's a kind of magic!
Tcham tcham!


Geyser Cola/ Mentos or Soda/ Candy

At first looks like a dangerous and silly prank, but if well done, on the right place is spectacular, and makes all adults want to be restless young minds.

Don't do this at home, chose an easy cleaning place!

What we need:

  • fotografar animais1 coke bottle, full,
  • 1 Mentos pack,
  • 1 cardboard, enough to "close" the bottle,
  • 1 test tube... or a paper funnel,
How to:
  1. Chose the place to this demonstration wisely, it will be messy, and you must be able to run away... fast;
  2. Uncap the coke bottle;
  3. Place all the Mentos (about 10) on the paper funnel, or test tube;
  4. If you are using a test tube , place the cardboard on the top and turn the tube upside down;
  5. If you are using the funnel close the end with the cardboard;
  6. Place the tube/funnel on the bottle uncapped top;
  7. Look around and chose a direction to run away;
  8. Remove the card quickly, so the candies fall in the bottle.
  9. Run!
Coca cola mentos geiser"Parents friendly" alternative
You can do this on a smaller scale, without the amazing geyser but with same effect, and best of all, without the mess.

What we need:
  • 1 glass,
  • 1 Mentos pack,
  • Coke or other carbonated drink.
How to:
  1. Put the glass inside a bowl;
  2. Fill half of the glass with your drink;
  3. Throw 1 Mentos inside;
  4. You don't need the running part.

Before any further conclusion, 
  • What happens isn't a chemical reaction! its a physical phenomenum, witch results in the sudden production of carbon dioxide resulting in a massive bubbling;
  •  If we look closer, Mentos surface is very rough... those irregularities are responsible for gas formation and sudden release.
  • Soda is made up mostly of water and sugar.
Knowing, these 3 things, lets try to find out what happen:

Carbonic drinks, like coke and other sodas, contain, as its name indicates, dissolved carbon dioxide. This gas is in equilibrium  and under a certain pressure- that’s the key the pressure- ready to escape as soon as the pressure on the liquid surface lower. All we know that’s necessary to remove the cap of the bottle with careful, without shake the liquid, otherwise all the drink will come out the bottle.
Until you open the bottle, the gas remains in suspension on liquid, and it can expand to form bubbles.
Note that if you place the soda in a glass and submerge a toothpick on it, its surface will form bubbles immediately.

Water molecules attracted each other strongly, holding the gas bubble in a kind of water molecules net. To form a new bubble or to expand the existing bubbles the water molecules must to move away from each other. Extra energy is needed to break this surface tension! In other words the water shows resistance to soda bubble expansion.

Coca cola mentos geiserIn this demonstration Mentos candy is going to perturb the coke equilibrium, the surface tension, this allows the CO2 to escape.

When you drop the Mentos on the bottle the surface tension is disturbed, and therefore the expansion and formation of new CO2 bubbles becomes possible. Mentos have thousands of micro holes on the surface those are called nucleation places- perfect places to form CO2 bubbles. As soon as Mentos touch the soda the bubble formation is initiated in its entire surface.
When all this CO2 is released from the bottle takes the liquid with it.

In conclusion:
This process depends greatly on CO2-under pressure- and on a element that disturb the tension -the element must be porous with nucleation holes), So we can conclude this demonstration can be done with any drink with bubbles like Sprite, beer, or even Red Bull.
We don’t know any other candy that works best then Mentos. They have thousands porous and heavy; they drown and don’t come out with the geyser.

Watch MithBusters movie "MythBusters - Diet Coke & Mentos":

Note that: Internet sources tells us that the use of diet coke works best because the low sugar ratio, witch delays the bubble formation

Mentos e Coca-Cola- Ciência Hoje

Et voilá!


Instant facts- Just add water 2

Pi, Greek letter (π), is the symbol for the ratio of the circumference of a circle to its diameter. Pi Day is celebrated by math enthusiasts around the world on March 14th. Pi = 3.1415926535…

Monday, November 21, 2011

Control digits- Portuguese Identification Card case- ISBN numbers

Each Portuguese identification card has a digit to the right of the ID number.
Countless stories have been created around this digit, most of them myths.

Although this article is in "answers to readers" section, there isn't any particular reader asking about this using the normal channels, but it's a question often brought to the conversion.

So, what is this digit?
Jorge Buescu, degree in physics from the FCL, PhD in mathematics from the University of Warwick and Professor of Mathematics at IST (1), explain this in his book "O mistério do bilhete de identidade e outras histórias"- "The mystery of the identity and other stories".

It's important to clarify
This digit isn't the total number of people with exactly same name as you. This is a urban legend, if you don’t believe me just take a moment to think about this:
This is always a 1 digit number, i.e., the range is from 0 to 9, so, if I have 9 people exactly same name as me it's nuts to think there must be someone with 12 or 14 people with exactly same name? The control number for those people should be higher then 9.

So what is this mysterious digit?
On same book Jorge Buescu, explains that "The extra digit is (or would be, if the Portuguese authorities hadn't committed a pathetic mathematical error!) Only a control number that detects if the number of the card is correctly written", and continues to explain that the human brain can't handle with hundreds of number with many digits if they don’t have a link between them, or a pattern. That’s why this method is used, so the computer can detect errors in the numbers. What would happen if a supermarket operator makes a mistake with the barcode numbers and "... charge 200 bucks for a butter package..." it would be unthinkable.

This number, if there wasn't an error, like noted by Buescu, would be used to detect if the Identification Card Number entered in database contained errors or not. 
This system of "digits detectors" is used in several other daily things such as credit cards, the ISSN for periodicals, the ISBN for the books, there are many other cases like those, where we use a control digit.

So how it works?
Buescu uses book ISBN as an example.
This number is usually in the back of the books and each title have a unique 10 digit number. For instance the ISBN for Buescu book "O mistério do bilhete de identidade e outras histórias", Edições Gradiva from collection "Ciência Aberta", is 972-662-792-3.
To check if the sequence is correct the computer applies the following formula:

x1+2x2+3x3+ … +10x10

Where ISBN number is:


The result, explains the author, is divisible by 11.

Try yourself:

ISBN:  972-662-792-3

Some of you, restless minds always on alert, would say: Some of the ISBN numbers have X's! Yes you are correct, some control numbers are not digit but letters, in those cases the 10 is represented by an X, that's due to the nature of used algorithm (2).
If you have a Portuguese identification card, you can try it yourself, do the same as the ISBN numbers, but read the number from right o left, like the image.

The pathetic mathematical error is that the number 10 (or the X in ISBN numbers) was replaced by a 0, so half of the people with control digit 0 should have a X.

(1) Buescu, Jorge. "O mistério do bilhete de identidade e outras histórias", Lisboa, Gradiva- Pulicações Lda, 2nd ed 2001

Et voilá!
Don't believe everything you ear

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