Weight of Light.

What I understood is that "The Pressure is too feeble for us to feel". But, when comets come closer to the Sun, we see cometary dust being spat out from the comet. Is that because of gravity not because of photons/light particles?

>> In free fall, the radiation pressure of the sun is enough to determine the direction of the very diffuse tail.

Thanks.

http://en.wikipedia.org/wiki/Radiation_pressure#In_interplanetary_space

Fifth paragraph says:

By the radiation pressure equation sT4/c; the sun-facing photon pressure is 3.61 µPa (3.6 N/km², 2.08 lbf/mi²). If the sun-facing surface is an almost perfect reflector, the force would approach double that (7.22 µPa) depending on how close to an ideal reflector the surface is polished.

Does that mean "If the sun-facing surface is an almost perfect reflector, the force will be almost double."

>  The energy of car increases, but the rest mass (which is involved in gravity) is unchanged.
It's true that the energy of car increases,
it's true that the rest mass is unchanged,
and it's true that the rest mass is involved in gravity.
But if you are implying that other forms of energy are not involved in gravity, that is untrue.
All forms of energy are involved in gravity, so if the energy of the car increases, so does its gravity.
(However, that energy had to come from somewhere, perhaps from fuel, so the total energy
of the car and the spent fuel and total gravity would be unchanged)