Physics
The force of friction between two surfaces will increase if:

Irregularities on both the surfaces are removed
The two surfaces are pressed harder
Air gap is created between the two surfaces
A layer of lubricant is kept between the two surfaces

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Physics
It is dangerous to observe Solar eclipse with naked eyes because

Infrared radiations from sun burn our retina
All radiations from sun initiate chemical reactions in eyes
Ultraviolet radiations from Sun burn our retina
Cosmic rays reach eyes more during the eclipse

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