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Absolute zero

The absolute zero temperature is the minimum possible temperature to every matter. This is equal to -273,15 ºC or 0 K. For this temperature, the particles movement is null. The 0 K temperature has never been reached. For example, liquid air is at 73 K (- 200 ºC).


Rainbows are formed in sky when solar light passes through small water drops (rain). The solar light is reflected and refracted when it passes through them. Then, each light wave length is refracted different angles, spreading the light in a spectrum of colors.

Speed Mach 1

The unit mach is used by supersonic airplanes to measure its speed divided by the speed of the sound at the altitude that it is flying. A speed of Mach 1 is equal to the sound speed (1220 km/h at sea level and 1070 km/hr at 11000 m altitude). Mach 2 is the double of the sound speed. When the airplane travels with speed above Mach 1, it is supersonic.

IS units

The abbreviation IS means, in French, Système International. In Portuguese, this abbreviation, IS, is entitled by International System. This system was agreed internationally by scientists with the aim that everyone publishes experimental results and calculations with the same units.


The echo that we hear in certain occasions is due to the repetition of a sound by its sound wave reflection. The sound wave is reflected in a barrier (rock, building), arriving later to us.

Distilled water

The distilled water is water turned pure by distillation treatment. Man should not drink distilled water because this contains small amounts of salts, being harmful for health because it dissolves the organism salts.


The abbreviation TNT is used for the compound trinitrotoluene. Although insensitive to heat and shock, when detonated, the TNT atoms rearrange forming products that have a volume a thousand times higher than the original. The formed products are water vapor, carbon dioxide and nitrogen gases.


The nettle leaves contain thorns with formic acid. This acid is responsible for the painful bites that we suffer when touching the nettle leaves. The formic acid is colorless and extremely painful. There are ants that use this acid as poison.

Graphite and Diamond

The graphite used in a pencil, for very strange that seems, it has the same composition as diamond. These two minerals are formed exclusively by carbon. The properties of these differ a lot because they have very different crystalline structure. While the graphite is used to write, the diamond is known as the hardest natural material.


The fireworks exhibition begins with a gunpowder explosion (activation). This reaction supplies the needed energy to excite the alkaline-earthy metals (elements of the group II). When these metals are excited they exhibit their characteristic colors. Alkaline-earthy metals as barium (Ba), magnesium (Mg) and strontium (Sr) are often used in pyrotechnics shows.


The compound 1-butanotiol is responsible for the characteristic smell of smelly weasels. The weasel segregates this compound in its own metabolism. This compound belongs organosulfurated groups, being more properly a tiol.

Conserve cans

The walls of conserve cans have a tin film deposit. You can verify that when you open a tuna can. The tin can be used in the alimentary industry because it isn't toxic. Apart from that, tin doesn't suffer erosion easily and it has the property of forming a uniform film deposited in the can surface.


Inside normal lamps the electric light is made in an inert atmosphere of Argon and Nitrogen (20%). Argon is an inert gas that doesn't reacts with tungsten filament when this is at very high temperatures (3000 ºC).


The matches head is made of potassium chlorate and sulfur. This also has phosphorus sulfur compound that, when rubbed in an abrasive surface, enters in ignition activating the rest of the match.


The nitroglycerine is mixed with powder wood producing the known it dynamite. The wood is used due to its high porosity, acting as a stabilizing substance of nitroglycerine. The nitroglycerine is produced with concentrated nitric acid.

Fireworks show

The components used in rockets for luminous effects are alkaline-earthy elements (Barium, Beryl, Calcium, Strontium, Magnesium). When subjected to a strong source of energy (gunpowder), each one of these elements emits an intense light with a certain color. The white color is produced by Magnesium, red by Strontium and green by Barium.

Human fatigue

When we make exercises, the oxygen lack in our organism originates the formation of lactic acid in the muscles. This lactic acid is responsible for the persistent muscular pains. The ideal conditions for organism to eliminate this acid are rest and a lot of oxygen (pure air).

Biological preservative

To preserve biological samples, biologists use formalin. This is an aqueous solution of formaldehyde, using methanol as stabilizer. The formalin especially has a very unpleasant smell.


As well as fog, milk is a colloidal mixture of oil drops (dispersed phase) with diluted liquid (dispersion middle). The oil drops have microscopic dimension being able to stay in suspension in the liquid.


The wine is a complex mixture of several compounds with water. In its composition there are hundreds of esters that contribute to its flavor and scent. However, the smell of the wine can be produced by the synthesis of the ethyl decanoate, being this one ester with low molecular weight.


The used fuels in space rockets are oxygen and hydrogen. These are stored at high pressures, in the liquid state. In the space rocket take off, oxygen and hydrogen reacts producing water vapor.

Aquarium fishes

The fresh water contains about 3% of dissolved oxygen. This oxygen is consumed by fishes through their gills. Therefore we should constantly oxygenate the aquarium water to prevent the suffocation of fishes.

Preservation herbs

The oxygen of air oxidizes food, producing a constant degradation of these. The sage and rosmaninho are herbs that can be used as preservants because they contain antioxidant components. These herbs can conserve food for long periods of time.


In the antiquity, the mercury was known as "liquid" silver. Although having unique characteristics and good appearance, the mercury is highly toxic and can emit vapors at any temperature. Thus it is being gradually retired of the market (thermometers).

Banana fragrance

The isoamil etanoate is the compound that gives has the banana fragrance. This ester is very used in the alimentary industry. The yogurt with banana fragrance has this compound. The same happens with chewing gum with banana fragrance.

Soap balls

The colors spectrum produced in the soap ball surface is a result of the light reflection. The visible light contains a spectrum of all colors depending on its wavelengths. The thickness of the soap ball film isn't uniform. Therefore, in the surface of the soap ball there will be zones with different color effects. The result is wonderful!

Plastic balls

The golf balls external part is made of balata. The balata can have natural or synthetic origin, being this last one the most used. On the other hand, the snooker balls are made of celluloid. The celluloid is a polymeric material that can acquire certain hardness, consonant to the wanted application.

Deodorant can

The deodorant is stored under pressure inside the can. When the can is used, a decrease in temperature is verified close to the diffuser. It is due to the abrupt dilation of pressurized gas inside the can. This Joule effect can be felt by you placing your skin close to the diffuser. That's cold!

Term bottles

The term bottles base their success on the high heat transfer resistance. The external wall is separated from the intern by vacuum, minimizing the convection and conduction of heat. That because when we have vacuum there are practically no molecules. Apart from that, the two walls are also covered with silver to minimize the heat transfer by radiation.


The methane has important domestic applications, being obtained mainly from fossil fuels. However, the methane is also produced by bacteria's in the absence of air. This type of methane is designated by bio-gas.


The computers microchips and of other electronic systems have gold covered electric contacts. The gold is used because it doesn't oxidizes and it presents good characteristics as conductor of electrons.


The glass is constituted by sand, sodium carbonate and calcareous stone. The sand is used to supply the main compound of glass, silica. To give a certain coloration to glass, iron oxide is used for a green coloration. On the other hand, the barium carbonate is added to produce a brown coloration.


The frying pans are covered by a Teflon film. This organic halogenated compound is very resistant to solvents, thermal stable and, mainly, it offers little attrition to food.


Soap is an alkaline metal salt (sodium potassium), acid, with a long aliphatic chain (5 to 14 carbons). The molecules extremities that constitute the soap have different polarities. One of the extremities attracts polar compounds (water) and the other attracts nonpolar (fats). It is due to this fact that soap presents the capacity to remove fats in molecular clusters (micelles).

Titanium dioxide

The titanium dioxide has countless applications when finely divided. It can be used to increase the opacity and whiteness of paints and paper. It can be also used in electronic components. Apart from that, when finely divided, this oxide can be used in acrobatics airplanes shows.

Fragrances of fruits

Esters of low molecular weight have characteristic fruits fragrances. For instance, butyl butanoate is a compound with pineapple fragrance. In the same way, the isoanil valerate has the apple fragrance. These esters are used broadly in the alimentary industry as synthetic aromas.


The gas hydrogen is the lightest gas providing a larger elevation for balloons and aircrafts (Zeppelin's). Since the Hindenburg accident, the balloons and aircrafts instead of using hydrogen they started to use Helium. Apart from being the lightest gas after hydrogen, Helium is significantly less reactive.


A parachutist in free fall at a certain moment reaches a terminal speed. On that moment, the gravity force is balanced by the air viscous resistance. Therefore, the parachutist starts to move with constant speed, not having acceleration.

Thick fog

Thick fog is a heterogeneous mixture of air and droplets of water. The droplets of water have very reduced dimensions, making possible the suspension in air. We have the formation of thick fog because the air surrounding the droplets is saturated in water.


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