[WillowTheWhisp]

Originally Posted by jambutty

Q48 – In a naturally aspirated engine, air enters the cylinder because of

Their answer – From atmospheric pressure pushing it in.

I selected from suction caused by the piston going down, which is the same thing. In fact it is probably more correct than their answer.

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.

Originally Posted by entwisi

Willow, the fact that the three small wheels are teh same size allows it to keep moving. if one was a different size then it would lock up as it would be trying to move faster than teh others which wouldn't be possible. as it is each is trying to move in exactly teh same direction and speed so it 'works'

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.