mechanical aptitude - Page 3

Neil · 11-10-2007, 22:16

Quote:

Originally Posted by WillowTheWhisp

I chose suction too

You need to understand what suction is to see why they asked the question and why they gave the answer they did. Suction - Wikipedia, the free encyclopedia

jambutty · 11-10-2007, 22:20

Quote:

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.

Neil · 11-10-2007, 22:21

This explains the gears a little better willow. Look how the outer gear is part of the gearbox casing so is held stationary. the 3 inner gears are fastened on a common plate and to the output shaft.

Epicyclic gearing - Wikipedia, the free encyclopedia

jambutty · 11-10-2007, 22:29

Quote:

Originally Posted by Neil

You need to understand what suction is to see why they asked the question and why they gave the answer they did. Suction - Wikipedia, the free encyclopedia

If you have two containers of differing air pressure and they are connected the air pressure will equalize in both. Whether it is sucked in or pushed in is a moot point and dependant on whether you are in one container or the other. If you are in the low pressure container the air is being sucked in. If you are in the high pressure container the air is being pushed out and if it is being pushed out of one it can be said to be pushed into the other.

It’s a bit like when you mix hot and cold water. Does the hot water make the cold water warmer or does the cold water make the hot water cooler.

The bottom line is that it is the movement of the piston that creates a vacuum and this vacuum sucks in the air. If the piston did not move the air from outside would not push it down.

WillowTheWhisp · 11-10-2007, 22:41

Quote:

Originally Posted by jambutty

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

OK, I meant teeth, The teeth being interlocked with the other teeth.

I knew what I meant.

Quote:

Originally Posted by Neil

This explains the gears a little better willow. Look how the outer gear is part of the gearbox casing so is held stationary. the 3 inner gears are fastened on a common plate and to the output shaft.

Epicyclic gearing - Wikipedia, the free encyclopedia

Yes, I suddenly had a blinding flash in which I saw it differently, hence my follow up post saying 'ignore that'

I'm still on the side of suction though.

entwisi · 12-10-2007, 06:36

I too went suction mainly as Jambutty said, the initial action that caused the movement of air is the piston going down. hence as it instigated the whole proceeding I reckon suction is right. Atmospheric pressure was only equalling the pressure so it wasn't pushed in as all,it was dragged across. To me pushed infers that 'positive pressure' is in action.

Well Done Jambutty though!

The ones that made me think were the multiple pully ones.

WillowTheWhisp · 12-10-2007, 07:07

You know the one where it showed you one pulley which was going clockwise and asked which others were going anti? I missed one of those off and I could kick myself because it was one of the ones right next to it!

Neil · 12-10-2007, 07:23

Quote:

Originally Posted by entwisi

To me pushed infers that 'positive pressure' is in action.

It depends where you are. In the cylinder you have negative pressure relative to outside it, outside the engine you have positive pressure relative to inside it. The air will move from a high pressure area to a low pressure one. That is why the air is pushed in. It's still works the same way in a turbo charged car.

You would not say the air is sucked out of you tyre when you press the valve in. The air will move from the high pressure inside the tyre to the low pressure outside. The word suction is commonly used when pressures under 1 bar are involved.

In the end it comes down to using the scientifically correct words. As in a bulb is where daffodils come from whereas light comes from a lamp. It does not really matter which way you describe it. They put that question in to catch people out.

I was discussing this with my mate, an ex fireman. He said they were always taught that if you are pumping water from a pond, the pump does not suck the water out of the pond. Atmospheric pressure acting on the surface of the pond pushes the water into the low pressure area created in the pumps inlet pipe.

The input to a pump is commonly known as the suction side and the output is known as the pressure side. That's stupid English language for you.

mrskitty · 12-10-2007, 07:44

I got 42%........

WillowTheWhisp · 12-10-2007, 07:50

Well I still reckon vacuum cleaners work by suction.

jambutty · 12-10-2007, 08:16

Ah! Yes! The multiple pulleys. That got my brain cell agitated a bit too but I got it right.

I got the electric fan question wrong and I’m damned if I can remember which was the other one.

What I can say is if the text were timed I wouldn’t have done so well. I don’t think quite as fast as I used to.

Air will always try to equalise if two connected containers have a different psi Neil. Whether you consider it pushing the air from high to low or pulling (sucking) the air into the low from the high isn’t really relevant.

When you withdraw blood from a vein does the hypodermic withdraw (suck) the blood out or is the heart pumping it out? You can still withdraw blood from a dead body therefore the blood is sucked out.

Re your analogy of the fireman’s water pump. You can still pump water out of a sealed container where air is prevented from replacing the removed water. It takes more effort but it can still be done. Therefore the water is sucked out.

I think that answer is to agree to differ on this issue but so far with three people opting for sucking against one person opting for pushing, the suckers have it.

jambutty · 12-10-2007, 08:25

Quote:

Originally Posted by WillowTheWhisp

Well I still reckon vacuum cleaners work by suction.

They do WillowTheWhisp.

But did you know that you can get compressed air to act just like a vacuum cleaner?

Take a long tube and part way down attach another tube to it at an angle. A bit like a capital Y. Blow air down the left hand part from top to bottom and it will suck air down the right hand part from top to bottom. It is quite a powerful suction too.

Neil · 12-10-2007, 10:07

Quote:

Originally Posted by jambutty

When you withdraw blood from a vein does the hypodermic withdraw (suck) the blood out or is the heart pumping it out? You can still withdraw blood from a dead body therefore the blood is sucked out.

No blood is not sucked out of a dead body. You create a low pressure in the syringe, the body is at atmospheric pressure, so the blood moves to the low pressure in the syringe.

jambutty · 12-10-2007, 13:02

Quote:

Originally Posted by Neil

No blood is not sucked out of a dead body. You create a low pressure in the syringe, the body is at atmospheric pressure, so the blood moves to the low pressure in the syringe.

But it doesn’t push the syringe plunger to create the vacuum. The nurse does that by pulling the plunger.

At some time in your life, surely you must have seen a nurse take a small bottle of sterilised water, stick a hypodermic needle into it through the rubber seal, draw off some of the water and transfer it to another bottle that holds the medication that will be injected into someone. There is no air in the bottle of sterilised water so the water must be sucked out.

According to the Oxford English Dictionary:
• verb 1 draw into the mouth by contracting the lip muscles to make a partial vacuum.
2 hold (something) in the mouth and draw at it by contracting the lip and cheek muscles.
3 draw in a specified direction by creating a vacuum.

Nothing to say about:
Re your analogy of the fireman’s water pump. You can still pump water out of a sealed container where air is prevented from replacing the removed water. It takes more effort but it can still be done. Therefore the water is sucked out.

The definition of a Suction Pump
Noun - a pump for raising fluids by suction
http://uk.ask.com/reference/dictionary/wordnetuk/178384/suction%20pump

Attach a vacuum pump to a bell jar and set it going. It will be sucking the air out of the bell jar.

Basically it amounts to - when you remove air or a liquid from somewhere you suck it out. When you put air or liquid into a container of some sort you pump it in.

shillelagh · 12-10-2007, 15:09

I got 50% 250 points. Okay i failed seeing as the passing percent is 80 but im happy with that seeing as im not mechanically minded even though i worked for an engineering company that made axles and worked in a fitting shop for a bus company! But it does show that i did pick something up otherwise it would have been worse.