Dear All, I'm afraid I've only just got back from a short holiday and so am a bit late in tossing my two penn'orth into the fountain...
I'm actually studying a solids and fluids course with the Open University at the moment and have just finished the fluids part (2 assignments due in next week), so should be about as capable as I'll ever be of tackling this question. For simplicity, consider the hose vertical and aligned to the centre of the bucket. This will set up a flow that goes down the middle of the bucket, radial out when it gets to the bottom, up the sides and radially back in to the middle at the top (roughly speaking). When the hose is inserted into the middle, it is basically being put into a liquid that is flowing vertically down - what is happening in the rest of the bucket I believe is relatively incidental. Tony mentioned that his hose had a jet attachment that fitted onto the pipe, and I think this is the crucial bit. If typical of such attachments it will be of a larger diameter than the pipe, probably twice the size, and increase in diameter in a series of steps, each perpendicular to the pipe. This means that fluid flowing along the outside of the pipe is then presented with a bluff (un-streamlined) body when it meets the back end of the jet attachment. Drag on bluff bodies can be considerable and I suspect that this accounts for the observed pull on the end of the pipe once it is immersed in the flow. This could be tested by removing the jet attachment and re-trying the experiment with just the bare hose. In this case there should be very little pull (any drag would be due to surface drag along the side of the hose). If the above is the correct explanation, the effect should only be particularly noticable once the jet attachment is fully immersed. Indeed it may need to be a little way into the liquid in order that some sort of flow is established along the pipe before hitting the jet. Not having a garden, I consequently have no garden hose either, so I shall have to leave it to you to experiment on my behalf - I hope I don't end up soaking too many of you through my suggestions! I hope I'm not too far off the mark in this explanation - it could have dire consequences come my exam in October!! David Higgon
