when I learned about torque and turning motion these were the sort of diagrams used, it's used to indicate a downward force of 300kg not a triangular item balanced on it's point
Andy (98% got fan one wrong)
The engine inlet one was another silly one IIRC, the the answer was one of either "air forced in by atmospheric pressure", or "air sucked in by piston downstroke", in their minds only one of those is right, whereas they're both right, the atmospheric pressure wouldn't force the air in without the piston downstroke.
Oh? I had no problem with that one.
Any physicist will tell you that suction is a fiction and flows are only cause by pressures. Things only move because a force acts on them.
It is not the removing of the table that causes the weight to fall to the floor but gravity. This is confusing the story with the physics.
nigelH
Certainly but if the piston doesn't move down, the air will not move into the cylinder, the atmospheric pressure remains the same, it's the piston moving that causes the change. The piston moving is the cause, the air moving in is the effect.
As I said you're mistaking the story for the physics.
You remove the air pressure on one side and the air pressure on the other causes the movement. Making something move means that work is being done. An absense of something does no work.
nigelH
You're answering a question that wasn't asked, they wanted to know what caused the air to flow into the cylinder, and that's where the ambiguity crept in, hence me saying both answers are right, the piston has to move and the air pressure has to act so which is the cause?
">> As I said you're mistaking the story for the physics.
Indeed the flow of air into the cylinder is caused by the *difference* in pressures between the atmosphere and inside the cylinder, not merely by the atmospheric pressure alone. It is the movement of the piston that causes the decreased pressure, which may be considered to be suction, when referenced to the outside atmospheric pressure.
Jeff
But surely the whole purpose of the question was to distinguish between people who knew the difference between these two answers. The other two answers, I seem to remember, were just silly space fillers.
The key words were suction and pressure.
The question was to test if you knew that suction was not an engineering concept. The 4 stroke engine was used as a trap because most of us learnt Suck/Squeeze/Bang/Blow long before we leant any real engineering.
nigelH
I'm not so sure about that, there were enough ambiguous questions in there for me to think c*ck-up rather than cleverness is more likely.. Atmospheric pressure alone can't make air go into a cylinder after all, but they mentioned the real cause (the cylinder going down) in one answer, but the mechanism for the movement (the air pressure) in another one. I suspect they were trying to trap people into claiming it was suction but they shouldn't have mentioned the piston going down, that's what made it ambiguous.
On or around Thu, 25 Oct 2007 14:52:06 +0100, "Nigel Hewitt" enlightened us thusly:
but, since I didn't bother looking at the answers, which did they say was "right"?
Ah, I deliberately left that one out, as I think you were going to go back through it?
If you want to know, scroll down;
The atomspheric pressure one.
On or around Fri, 26 Oct 2007 09:58:29 +0100, Ian Rawlings enlightened us thusly:
ah, OK. I might go back through, but on that one, it'd answer the same, and in fact I got it right anyway.
wonder which ones I got wrong apart from the electrical one where I clicked the wrong thing by mistake.
Hey Austin, I just tried that and got 100%. Nearly did'nt though, had to re-read the balloon one and changed my mind as I did'nt notice at first that it said all contained the same amount of gas which meant the atmospheric pressure was not a constant.
Martin
On or around Fri, 26 Oct 2007 21:05:07 +0100, "Oily" enlightened us thusly:
ah, could've been that. the picture/question is ambiguous, though, in that it implies that they're in the same space. If the balloons are in 2 different locations, then the answer is as you said and not as I put. I'm sure the strength of the balloon comes into it as well :-)
It's a bit misleading to have a picture of them all together, that's what nearly fooled me, but I don't think it was a trick question as they are all elementary stuff and so long as the balloons are elastic, I don't they intended you to think that deeply about it. The one that I spent more than a few seconds on was counting the effort reductions on all those pulleys, nearly counted that one wrong except that there wasn't answer to correspond with the one I first came up with. An entertaining few minutes though, cheers for the link.
Martin
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