Question

Is it totally correct to say that the earth is in free fall (around the sun)? I guess because the only force the earth experiences is gravity because there is no friction or air drag in space but perhaps there is some other force in space?

Answer 1

Well, not exactly. Space is not an exact vacuum. I can think of the example of the sun emitting solar rays, these rays have all kinds of energy (photons) and matter (sub atomic particles) involved in them. There must be some kind of force acting with and against the motion of the earth through this solar ray bombardment.

I draw your attention to the concept of a solar sail, which harnesses these rays to act as a propulsion: http://en.wikipedia.org/wiki/Solar_sail

Answer 2

The force that the solar wind plays on the Earth is infinitessimal so effectively yes, you could see the Earth as free falling around the sun. The solar wind wouldn't exert drag, as it's emitted from the Sun at all in every direction, so at any moment it should be moving perpendicular to the direction of the Earth's movement. Any effect it would have would be to reduce the draw that the Sun's gravity has on the Earth.

Meteors and dust may have an effect, but again their impact (!) would be tiny.

Amongst the forces (gravity, weak nuclear, strong nuclear etc) gravity is the only one that has any significant effect at the scale of the Earth and the Sun

Answer 3

Or if you believe Einstein (and the recently published results of the Gravity Probe-B see: http://einstein.stanford.edu)) then the Earth is essentially moving in a straight line through the curved space around the Sun.

Answer 4

I like to think of the earth as moving in a straight line through curved space-time. That is a wonderful ref link - thanks Dr. Neutrino.