Heating, Cooling and HVAC

Q.Why is the Earth spherical and not any other shape?
A.The answer lies in the gravitational force,which pulls every object towards each other. The Earth is thought to have formed from a huge, rotating cloud of gas. In the newly born Earth, gravity pulled parts at the same distance from the centre with the same force. This means that matter equidistant from the core in all directions finally settled into a sphere.

Q .Why does each country have its own money system?

A.Most countries have their own system so that their economy isn’t dependent on some other country’s economy. Not all countries have done this. Several South American countries have been considering adopting the American dollar as their own currency, as a way to introduce economic stability. Another example of the consolidation of currencies for the purpose of economic stability is the euro.

Q.Why is sea water salty?

A.Rivers erode minerals from rocks and soil and deposit them into oceans. Those elements include sodium and chlorides, which, when combined, become salt. And although rivers transport salt, they themselves don’t become salty because the oceans are their dumping ground. Fresh water from the rivers evaporates as the sun warms the oceans; the salt stays behind.

Why Do Mosquito Bites Itch?

The female mosquito wants to drink your blood, but doing that is not easy. Blood clots very quickly on contact with air, too quickly for mosquitoes to have a drink. So, the mosquito injects a small drop of “poison”. It’s not really a poison, but a chemical that stops your blood from clotting long enough for the mosquito to have a drink. Your body then sends chemicals called histamines to the area where you were injected. It’s the histamines reacting with the “poison” that cause the itching, swelling and redness.

Why do certain items glow in the dark?

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A phenomenon called phosphorescence is responsible for the light that most glow-in-the-dark items emit.

Phosphorescence occurs when light absorbed by an object is slowly released and can be observed even after the light source has been removed. If not tampered with, such light is dim and pale blue in colour.

Chemists had the bright idea to make this phenomenon visually stimulating. They discovered that when the phosphorescent material was mixed with fluorescent dyes, the object emitted a glowing bright green or sometimes red light.

The reason for this transformation is that fluorescent compounds absorb light and rapidly emit it, giving the compounds a glowing appearance. However, this phenomenon occurs only in the constant presence of the original light source.

The pale blue light emitted by the phosphorescent material is, in turn, absorbed by the fluorescent dye. And the light now emitted is green or red, depending on the type of dye used.

The most commonly used phosphorescent material is zinc sulphide mixed with copper, and the green fluorescent dye is mostly sodium fluorescein. Likewise, the red fluorescent dye is usually rhodamine. Paired together, the phosphorescent and fluorescent materials produce a ghostly, glowing green or red light, which is often used to make toys and decorative items attractive.

Source:The Telegraph (Kolkata, India)