What is speed of light in vacuum? How does vacuum, force and air effects speed of light?

Speed of light is maximum in vacuum and it is 300000 kilometers per second. Isn't is too fast?

When Light enters the earth's atmosphere, it collides with air particles, which slow them down. The speed of light in air is slightly less than the speed of light in vacuum. Collision of air particles with light makes the light slows down.
Huge forces ( Like gravitational pull by black hole) slows down the speed of light to the maximum. Even light can escape black hole.
In vacuum there are no particles, hence, light travels without any hindrance with maximum velocity in vacuum.