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What is friction and its types?

‘Friction‘ is a force that resists motion of sliding or rolling of one object moving relative to another. It is a result of the electromagnetic attraction between the charged particles of two touching surfaces.   Types of Friction Static Friction : It is defined as the frictional force that acts between the surfaces when they are at rest with respect to each other. The magnitude of the static force is equal in the opposite direction when a small amount of force is applied. When the force increases, at some point maximum static friction is reached. Rolling friction : It is the force that resists motion when an object rolls on a surface. Technically it’s not friction; its ‘rolling resistance’ since when a body rolls perfectly upon a surface, on paper, there is no sliding friction between that object and surface. Sliding friction : It is the frictional force between two surfaces that are rubbing against each other. It’s a very easy and common concept. It’s hard to find a perfectl...
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What is Presbyopia?


Presbyopia is the gradual loss of your eyes' ability to focus on nearby objects. It's a natural, often annoying part of aging. Presbyopia usually becomes noticeable in your early to mid-40s and continues to worsen until around age 65.

Symptoms of Presbyopia

People commonly mistake the symptoms of presbyopia for longsightedness. However, the two conditions have different causes: longsightedness is a result of a misshapen cornea, whereas presbyopia is due to the loss of flexibility in the lens.

The telltale symptom of presbyopia is blurred vision while reading, sewing, using a mobile phone, or doing anything that requires near vision.

Treatment for Presbyopia

There are many options for people with presbyopia, including contact lenses. Recent technologies allow people who are entering into presbyopia to continue wearing contact lenses, instead of having to switch to bifocals, or reading glasses.

Common treatments for presbyopia include :

  1. Magnifiers
  2. Bifocal or varifocal spectacles
  3. Reading glasses

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What is friction and its types?

‘Friction‘ is a force that resists motion of sliding or rolling of one object moving relative to another. It is a result of the electromagnetic attraction between the charged particles of two touching surfaces.   Types of Friction Static Friction : It is defined as the frictional force that acts between the surfaces when they are at rest with respect to each other. The magnitude of the static force is equal in the opposite direction when a small amount of force is applied. When the force increases, at some point maximum static friction is reached. Rolling friction : It is the force that resists motion when an object rolls on a surface. Technically it’s not friction; its ‘rolling resistance’ since when a body rolls perfectly upon a surface, on paper, there is no sliding friction between that object and surface. Sliding friction : It is the frictional force between two surfaces that are rubbing against each other. It’s a very easy and common concept. It’s hard to find a perfectl...
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What is non-metal?

A non-metal is a material which do not have properties of metals like lustre. They are non malleable, non ductile, non sonorous and bad conductor of heat and electricity. Example- Carbon, Sulphur, Phosphorous. Non-metals are the elements which form negative ions by accepting or gaining electrons. Non-metals usually have 4, 5, 6 or 7 electrons in their outermost shell. Very few elements in the periodic table are non-metals. These are present on the right-hand side in the periodic table. Elements that come under non-metals are sulphur, carbon, all halogens, phosphorus, hydrogen, oxygen, selenium, nitrogen and noble gases. Properties of Non-metals : High ionization energies High electronegativities Poor thermal conductors Poor electrical conductors Brittle solids-not malleable or ductile Little or no metallic luster Gain electrons easily Dull, not metallic-shiny, although they may be colorful Lower melting points and boiling point than the metals  Some special facts : Uses of non-...
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Why is the Earth called Blue Planet?

“The Earth has almost 70% water on its surface due to which it looks blue in color”. or “ More than 71% of the earth is covered with water. Hence, its is known as the blue planet ”. Why Earth looks blue from space? The Earth has extremely hot red heat under its crust and the top outer surface is covered with water. The Earth’s surface has many oceans and seas starting from the Arctic Ocean to the Southern Ocean. These oceans & seas cover almost 70% of Earth’s surface and the remaining 30% is covered with land. It means that almost 70% of Earth’s surface appears blue from outer space & the leftover 30% looks greenish-brownish. This is the reason why Earth looks blue from outer space.  
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