How is the light produced when an object is burnt?

A chemical reaction is a simple rearrangement of atoms leading to formation of newer substances(products). Hence, to favour the rearrangement,breaking of bonds in the reactants and making of bonds between atoms in the products occur.
Due to this in every chemical reaction there is involvement of energy (liberation or absorption depending on the bond energies of the elements in the reactant and the products). The energy involved may be light, heat or electrical energy.
All combustions (burning) are chemical reactions of a fuel with oxygen in which carbon-hydrogen and oxygen-oxygen bonds are broken in the reactants (except hydrogen) and carbon-oxygen and hydrogen-oxygen bonds are formed in the formation of the products.
The bond energies of these atoms are in such a way that the energy liberated is always more than the energy consumed for the breaking of bonds. The net energy is liberated in the form of both light and heat.


Why is fire hot?

Chemical reactions can be either exothermic(heat liberation) or endothermic (heat absorption). Oxidation reactions are exothermic and reduction reactions are endothermic. Combustion is an oxidation reaction and hence is exothermic.
All liquid,solid and gaseous fuels contain any one of the three combustibles constituents viz, carbon, hydrogen ans sulphur. When a fuel is burnt the heat liberated makes the products of combustion hot. The products of combustion are carbon dioxide, water vapour ans sulphur dioxide. Along with these, the unused oxygen in the atmospheric air supplied for combustion and also the entire quantity of nitrogen which is the major constituent in the air are also heated. That is why fire is hot.


How does one control the movement of hot air balloons?

Hot air balloons rise ito the sky because of the fundamental property of the hot air filled in them; air when heated becomes lighter (less denser) than the surrounding cold air. The balloon does not have controls such as accelerator, steering or brake. It is driven by breeze and so there is no control over the flight path. Ascending is by heating the air with the help of burners suspended beneath it. As a result, the balloon rises to find its equilibrium with the surrounding air. Descending is by releasing the hot air from the balloon. Hot air balloon enthusiasts venture out after studying the weather and making sure there are no strong winds.


Why do two great tastes sometimes not taste great together?

Among the five tastes, salty, sweet and umami (meaty or savory) are appetitive, driving us toward essential nutrients, whereas bitter and sour are aversive, alerting us to potentially harmful substances. Mixing the aversive with the appetitive sends conflicting information to the brain, and confusion is what the senses are trying to avoid as they supply you with useful, lifesaving information. This mixed signal is why you reject food that has gone off. You do not want to eat a blend of the good and the bad.
Yet consider the phrase “sugaring the pill”: pills are medicine and as such are poisonous in large quantities. They thus taste bitter but can be made more palatable by a camouflaging sugar coating. Similarly, coffee can be improved for people who are sensitive to bitterness by masking its sharpness with cream or sugar.
As adults, we can override these warnings and acquire tastes for coffee, olives or strong cheese. But you will confound your senses if you mix a formerly aversive taste with an appetitive one. (Care for some pickles and cocoa?) There can be delight in the confusion, however: sweet and sour is a popular choice in Chinese cuisine.


What is Nucelar Winter?

Nuclear explosions trigger a horrendous chain reaction. The instantaneous outcome is the thermal and blast effect annihilating everything in and around the area. The mushrooming cloud due to the explosion rises high into the stratosphere, spreading out vast quantities of soot and radioactive debris. Some of the debris fall back to the ground as rain out. The soot and other particles suspended in the atmosphere would block sunlight and lower the global temperatures steeply to subzero levels, ushering in wintery conditions over the planet. This sequence of events has been termed as "Nuclear Winter". As a consequence, photosynthesis would stop leading to the destruction of all green plants.
Subsequently oxygen regeneration would cease and carbondioxide would accumulate. Earth's radiation balance and heat budget would get altered leading to drastic changes in the global circulation pattern. the seasonal monsoons and tropiacl rains may disappear. the duration and extent of the nuclear winter scenario would depend on the location, season and intensity of the explosion.


Why are fishes not able to survive in distilled water?

If the fish is in distilled water, there is an osmotic flow of water from outside the fish to the inside because the salinity of the fish body is higher than that of water. Thus there is danger of dilution of the body fluids of the fish or at worst that of being blown out if the fish is to be in distilled water for a very long period of time.


Diamond is a good thermal conductor. But it is an excellent electrical insulator. How?
Diamond crystal is a three-dimensional network of carbon atoms. All carbon atoms in the network are strongly bonded by carbon-carbon covalent bonds.
Therefore diamond crystal has a highly symmetric cubic structure. The carbon atoms in diamond are precisely aligned. Thus diamond is an ideal crystal. Atoms in the crystal lattices in solids vibrate.
These vibrations, called the atomic vibrations facilitate thermal conduction (transport of heat) in solids. In an ideal crystal, the lattices are so precisely aligned that they do not interact with each other.
Therefore an ideal crystal conducts better than a non-ideal crystal resulting in ideal crystals having good thermal conductivity, which is a measure of heat conduction. Diamond being an ideal crystal is thus a good thermal conductor.
Mobile electrons facilitate electrical conduction - flow of current in solids. There are no free mobile electrons in diamond crystal to ficilitate electrial conduction. Thus diamond is an excellent electrical insulator.


Why do houseflies rub their front legs together?

Housefly (Musca Domestica) is a common insect found in all places. It has a very short life span. Adult houseflies feed on human and animal food and waste materials and often use buildings as shelter.
The housefly is well adapted in structure and behaviour to transmit disease causing organisms from place to place.
The body of a housefly is covered with fine hairs and bristles that readily pick up filth particles.
At the base of each leg there is a cushion-like structure covered with granular hairs.A sticky secretion which excretes from the granular hairs gathers bacteria and other micro organisms which stick to the legs. In order to clean its body and the legs, houseflies rub their legs together. It is estimated that whenever a housefly rubs its legs, lakhs of bacteria are discharged from the legs for each rubbing.