Why does a flame always point upwards?

Hot gas is generally less dense than cool gas. A flame is very hot gas. Gravity pulls less on less-dense gas, so hot, less-dense wants to rise above cooler, denser gas. As the flame burns on earth, it takes the oxygen from the atmospheric air and and heats the surrounding atmospheric gases. So the hot air around the flame is pushed up as it is less dense And as the air around the flame is pushed up , the air around the flame is drawn towards the flame to take the space of the lighter gases that is pushed up. The colder air surrounding is pulled down by gravity. The flame is being pressurised all around by the atmospheric gases. This results in the flame being elongated upwards. 

In space, where there is no gravity, a flame does not point upwards but will expand spherically around the source.

Why do we sometimes see double rainbow?

Rainbows are a bright spectrum of light that appears in the sky when light reflects off moisture in the air. Double rainbows are less frequent, less bright and usually sit outside the first rainbow. They occur because of a double reflection of sunlight off moisture and appear at an angle of only 50 to 53 degrees.

When refraction occurs to cause single rainbows, the light strikes and goes through moisture. Double rainbows are created in the same way except the sunlight bounces twice off the moisture before re-entering the sky.  The second rainbows are fainter than single rainbows. This is because the light has been reflected twice and had two chances to be transmitted out the back of moisture in the air. 

This second reflection inverts the colors when dispersion occurs. The region between a double rainbow is dark.

What is dry ice?

Dry ice is pure, solid carbon dioxide (CO2). As a gas, CO2 exists naturally in our environment.  It's called "dry ice" because it does not melt.  Dry ice goes directly from a solid to a gas in a process called sublimation.

Dry ice keeps items colder for much longer than traditional 'wet ice' because dry ice is extremely cold, -109 degrees F (-78.5° C).  Dry ice sublimates into carbon dioxide gas instead of melting, leaving no liquid mess to clean up. Dry ice is made from pure carbon dioxide that is a (recycled) byproduct of other industrial processes such as the manufacture of ethanol.

Dry ice is much colder than regular ice, and can burn the skin similar to frostbite.

Why is Pluto no longer a planet?

American astronomer Clyde Tombaugh discovered Pluto in 1930. However in 2006, the definition of a planet was changed. 

According to new rules adopted by the International Astronomical Union, a celestial body must meet the following criteria in order to qualify as a planet:

1. A planet must be round.

2. A planet must orbit the sun.

3. A planet must have "cleared the neighborhood" of its orbit. This means that as a planet travels, its gravity sweeps and clears the space around it of other objects. Some of the objects may crash into the planet, others may become moons.

Pluto follows the first two rules: It is round, and it orbits the sun. It does not, however, follow the third rule. It has not yet cleared the neighborhood of its orbit in space. Because it does not follow this third rule, Pluto is no longer considered a planet. It is called a dwarf planet.

Why are coin banks shaped like pigs (piggy bank) ?

In earlier times, metal was expensive and seldom used for household wares. Instead, dishes and pots were made of an economical clay called pygg. Whenever housewives could save an extra coin, they dropped it into one of their clay jars.They called this their pygg bank or their piggy bank. When an English potter misunderstood the word, he made a bank that resembled a pig, and it caught on. This name caught on because the pig banks were mostly used by children, and a pig is a child-friendly shape that is easy to make out of clay. Once the meaning had transferred from the substance to the shape, piggy banks began to be made from other substances, including glass, plaster, and plastic.

Why do some animals eyes glow at night?

Animals, especially ones who are active at night, have a reflective surface behind their retinas.  That surface is called a tapetum lucidum and it helps them see in the dark.  Basically its job is to reflect light, like a mirror, in the eye to allow what little light there is at night to hit photoreceptors in the eye. Light passing into thetheir eyeballs bounces off from the tapetum lucidum, giving the animal the ability to reflect what little light is incoming, thus allowing it see in near darkness. Due to the reflection, their eye glow. Human eyes don't shine/glow because they don't have this layer of tapetum lucidum. 

Why wool keeps us warm than cotton?

Wool is a bad conductor of heat and its fibers can trap air in between themselves. Air is also bad conductor of heat. So, woolen clothes do not allow the heat in our body to escape, i.e, they trap the heat inside our body to keep us warm. That is why we feel warm when we wear woolen clothes. Cotton clothes allow more of this warmed air to "leak out" through the thinner fabric.

Why cannot a petrol fire be extinguished by water?

Petrol as a liquid is less dense than water. As water is thrown onto the petrol, the petrol floats on top of the water and continues to vapourise. It is the vapour which burns, slightly above the surface of the petrol. Also, if small quantity of water is poured over burning petrol, the existing temperature is so high, that the water poured on the fire evaporates even before it can extinguish the fire. 

Why spiders do not stick in their own webs?

The spiders that make webs and use their silk to capture their prey. If a fly or other insect moves into the web, it becomes entangled. There are a couple of reasons why spiders manage to stay clear of entanglement in their own web. A spider actually has very minimal body contact with its web. Its legs are covered with hundreds of little hairs that serve to decrease the total surface area the web can stick to. Spiders use a very careful walking technique with movements that let the strands of web slip off very easily. They are good groomers. Careful cleaning ensures that its legs and body are less prone to sticking, should they suffer a misstep in the web. And additionally, the hair on the legs are covered with a special chemical that prevents the web's sticky coating from adhering.

Why does water remain cold in an earthen pot?

An earthen pot is made of mud and becomes porous with a very fine holes all over. When water is poured in the pot,  it first spreads itself on to the walls of the pot.This water percolates in the pores to the outer surface. Here evaporation of water takes place thereby producing a cooling effect. The pot becomes cool and also makes the eater inside cool. If you observe, the cool water level is lesser than the intial water level when poured.

Why do we have silent alphabets in English words?

There are hundreds of rules to help figure out how to spell and read words, but they do not work all the time. There are more exceptions than rules. :)

Silent letters show up because English has a lot of influences. Many words in the English language are derived from foreign words. English takes words and spellings from many different languages. A lot of times, when there is a silent H at the begging of a word, it comes from a rule in French language pronunciation. That’s why hour sounds like our. Silent Ks come from Old English, which was spoken in England before 1100 CE. They actually used to be pronounced, but over hundreds of years, the sound was dropped, leaving us with the words knife and knight, where we don’t pronounce the first letters. 

Since accent and pronunciation differ, letters may be silent for some speakers but not others. 

Why do some things melt and some things burn?

Melting and burning are actually quite different processes; melting is an example of a physical change while burning is an example of a chemical change. Most materials have high melting point. Combustion temperature determines when the material will burn.

The energy required to start the reaction (called the energy of activation) determines whether the material will melt or burn. This energy is in form of temperature or other conditions like oxygen availibilty etc. For some materials, the melting point is much higher than the combustion temperature, hence they burn before they can melt.

Why does Your Nose Run When You Cry?

Tears leave the surface of your eye by evaporating or by falling of from eye surface or by entering the tear drainage system. A thin tube drains the tears from the inner corner of the eyelids down into the nose. Therefore, when your eyes fill with tears, such as when you cry or cut an onion, most of that fluid ends up in your nose. Tears mix with mucus there and your nose runs.

Why does a year have 12 months?

All calendars began with people recording time by using natural cycles: days, lunar cycles (months), and solar cycles (years). Ancient Egyptians followed lunar calendar for the year. New moon occurs every 29.5 days. We have twelve months because there are twelve periods from full moon to full moon in a year. Thus ancient Greek calendar had 12 months of 30 days. The lunar calculation however when summed up, did not fit the solar cycle. This was evolved gradually to have unequal 12 months. This evolved Egyptian year was almost a quarter of a day shorter than the solar year.  Julius Caesar hired an ethnic Greek from Alexandria Egypt to create the 365 day calendar with an extra day every fourth year (leap year). We now follow Gregorian calendar.  

Why do fingernails grow faster than toenails?

The nail is an important structure made of keratin that has 2 purposes. It acts as a protective plate and enhances sensation of the fingertip.

It takes fingernails 3 to 6 months to regrow completely, while taking toenails anywhere from 12 to 18 months. The rate of nail growth is based on the length of the outermost finger bones. Therefore, fingernails grow faster than toenails and the nail of a person's index finger grows faster than their pinky fingernail. The blood supply to the fingers is almost always better than the blood supply to the toes. The rate of nail growth may reflect this.

Why does long exposure to sun lighten our hair but darken our skin?

Our skin and hair has a brownish-black pigment in it called melanin, which gives them the certain color. Our skin is a living tissue. When we are exposed to the sun the rays, the ultraviolet rays cause the skin to produce more of melanin, which helps to lessen the damage caused by radiation. Production of more melanin darkens our skin and protects it against furthern UV radiation. The lighter our skin, more likely that our skin burns because our skin can not produce sufficant amount of melanin.

Our hair on the other hand is dead and can not continue to reproduce anything. So when exposed to radiation by the sun, the hair gets bleached.  It starts to fade color since no new melanin is produced to protect the hair. The root of hair produces melanin which will give color to only the new hair growing, but not the faded hair.

Does ice melt faster in air or in water?

Ice melts when heat is transferred away from it to its surroundings. Water is denser than air, so heat is conducted away from the ice faster in water than in air. 

Ice will melt fastest in whatever delivers heat to it fastest. In general that will be water because water conducts heat and carries heat better than air. But extremely hot air, such as that from a torch, will beat out very cold water, such as ice water, in melting the ice.

Why do veins look blue if blood is red?

Blood is ALWAYS red. Oxygen-rich blood is bright red as it leaves the heart. When it returns in veins without much oxygen, it’s still red, but it’s a deeper, darker red. But our veins look blue. Ever wonder why?

The colors we see are the result of which wavelengths of light are reflected back to our eyes. Veins appear blue because blue light is reflected back to our eyes even though veins contain deep, dark red blood.  Blue light does not penetrate human tissue as deeply as red light does. As a result, veins that are close to the surface of the skin will be more likely to reflect blue light back to the eye. The oxygen-depleted blood that veins carry also tends to absorb red light more than blue light. When the dark red blood absorbs more red light, blue light is more likely to be reflected back to our eyes.

What are wisdom teeth and why are they called so?

Wisdom teeth are the third molar teeth. They are located all the way back in the jaw, and tend to come in some time between the ages of 16 and 25, if they come in at all. For many people their wisdom teeth coming in impacts other teeth, requiring surgery to remove the wisdom teeth to allow their jaw to remain healthy. Generally infants form a first set of teeth, commonly called baby teeth, which eventually fall out and give way to the adult teeth, that will remain until old age. Wisdom Teeth come quite a bit after the full set of adult teeth have grown.

Wisdom teeth are so named because of the time they appear, generally in the late teens or early twenties, when people are  presumably "wiser" than as a child, when the other teeth erupt.

How do fish sleep?

Most of the fish do sleep.  The way they sleep is slightly different than the way humans and lots of other land animals sleep. Fish have a period of reduced activity and metabolism which seems to perform the same restorative functions as nocturnal sleep does in humans.Most scientists agree that the way fish sleep might be more like what we consider rest. The sleep of fish involves spending time staying mostly still, conserving energy.

What is the difference between a fruit and a vegetable?

Generally we tell apart fruits and veetables based on how they taste and how they are eaten or cooked. We think of fruits as foods that grow on trees, taste sweet, and can almost always be eaten without cooking. We tend to think of vegetables, as foods that grow in or near the ground, and are eaten after cooking, sometimes can be eaten raw too. 

According to science, a vegetable is any part of a plant that can be eaten, like leaves, stems, or roots. So vegetable is any edible part of a plant. A fruit is also the edible part of a plant, but refers specifically to the edible part of a plant that has come from its ripe flower. The major fruit and vegetable difference is that most of the fruits contain seeds, which are capable of developing into new plants and vegetables lack seeds (there are exceptions to this though).

Why does milk overflow when boiled but water does not?

Milk is not a simple liquid - it contains tiny globules of fat and casein which are not dissolved but suspended in water.  When heated, fat being lighter than water, floats as a creamy layer on the top and water vapor, in the form of steam bubbles, is trapped under it. Further heating results in the formation of more number of bubble. These bubbles expand and lift the creamy layer causing it to overflow. 

In the case of water, the steam bubbles break as they reach the surface. No film is formed and the bubbles of steam formed by boiling escape easily without any resistance. Hence, water does not overflow on boiling.

Why do we blink our eyes?

We blink our eyes every six seconds. Although blinking eyes ins an involuntary action, we can raise or lower the number of blinks voluntarily. Blinking our eyes automatically supplies two forms of safety to our eyes, to keep them from drying out, and to keep foreign matter from entering and irritating our eyes. The rims of our eyelids are lined with 20-30  oil-producing glands. Blinking automatically coats the eyelid and eyelashes with the lubricant it secretes, to prevent them from drying out.

When we are concentrating on a particular thing or looking continuously on a keyboard, screen, needle, etc we blink less as compare to the normal situation. This happens because our brain forgets to blink as a result our eyes feel tired. Research has shown that we blink more quickly when we are not interested in a particular task and also not taking the information inside for processing and vice versa. Some animals like the snake for example, do not have eyelids and hence cannot blink. But there is a hard film or scale over the eyes to protect them from dust and injury.