[jambutty]

Originally Posted by WillowTheWhisp

I chose suction too and I'm still convinced that is more right than their answer but I can see the logic of 'air pushing into a vacuum' but to my logic air is sucked into a vacuum.



If the outer rim didn't have cogs then I would agree with you Ian, but the cogs in the outer rim are locked into the cogs in those three small 'planetary' wheels which in turn are locked into the central 'sun'. In any series of gears if one of the cogwheels is held rigid then it prevents the movement of any wheel it interlocks with. So I still say they couldn't possibly move. Now if that outer rim was smooth then of course the three planetary wheels would slide effortlessly within it and their answer would apply, but the rim in the image is not smooth.

If the piston didn't move their would be nowhere for the air to go. So we were right and they were not wuite so right.

The outer rim doesn’t have cogs – it is itself a cog and it is locked.

The sun may be fixed on its axis but the planets are free to move rotationally and laterally.