[El Gato]

On Earth there is always air or water available to push against.

Ok so they should have said "push with" or "expel" or somesuch. Give 'em a break. Physicists, like engingeers don't always have the best writing skills. I'm a perfect example of that, my writing skills are pretty minimal, although I do better than many engineers, especially the youngsters.

[cinFLA]

Physicists, like engingeers don't always have the best writing skills.

But they are usually technically accurate and do not write in the jargon of the uniformed layman.