How good is YOUR mechanical knowledge?

[deanohit]

Managed 380points, 76%, not bad I thought. Was a pretty cool test, would help if they showed you where you went wrong.

[sAsLEX]

Managed 380points, 76%, not bad I thought. Was a pretty cool test, would help if they showed you where you went wrong.

It does, little button up on the right looks like a mag glass maybe

Am I the only one who has seen this

[carbacca]

86%...and i am a fricking mechanical engineer

[steveb64]

Air is being pushed into the motor by air pressure. It it only filled due to sucking, then something like a supercharger sitting across the inlet tract would be a restriction. A supercharger works because it pumps more air into the motor. I'm surprised anyone would quote 'howstuffworks' as an authority on anything!

Errm - the question was relating to a "Normally Aspirated" engine. Turbos and superchargers work by 'pumping' air, thus PUSHING more air into the cylinder than can be sucked in by the piston alone, thus increasing the charge amount and pressure, even before the piston begins its compression stroke...

IMO - they deliberately screwed up some of the answers just so NOBODY can get a perfect score...

[deanohit]

It does, little button up on the right looks like a mag glass maybe

Am I the only one who has seen this

Ummm, yea, I think only you noticed it. Oh well, I'll do it again later and see if I've improved.

[steveb64]

There isn't if you have one pulley, no matter which direction you pull you are lifitng the same weight. There is only a mechanical advantage when you have multiple pullleys an the ropes setup in teh right arrangement.

Oh yeah, i got 82%. That electrical circuit one is confusing, the terms they use aren't really widespread in the industry in NZ.

Oh. Well, ya learn summat every day. I knew multi pulleys changed leverage ratios - just not singles...

Eleccie stuff was pretty much as I learned it...

[imdying]

Errm - the question was relating to a "Normally Aspirated" engine.

No shit... just like your reply, only the first sentence was directly related...

[steveb64]

It does, little button up on the right looks like a mag glass maybe

Am I the only one who has seen this

Probably! I have to confess, I had to look further into the forum that I found this on, to spot the 'recheck' option.

But I thought it'd be more fun to see who spotted it here, without being pointed at it first... Top marks for observation!

[moT]

yeah 66% i think i need a mechanic

[steveb64]

No shit... just like your reply, only the first sentence was directly related...

Ok, so I'm NOT as good with my wording as I could be... I'll try it differently...

IMO - If the air pressure in the inlet tract is higher than ambient pressure, air is being 'pushed' into the engine. If the pressure in the cylinder is at ambient or higher, then air is being 'pushed' into the cylinder.

If the air pressure in the inlet tract is at ambient (or higher), AND the air pressure in the cylinder is less than ambient, then air is being 'sucked' into the cylinder.
Regardless of whether or not there's a turbo/super charger involved.
Until the cylinder reaches ambient pressure - air is being 'sucked' in (even if only for a few milliseconds).
After it reaches ambient pressure - if more air/charge is entering the cylinder, then it is due to it being pushed in - either by turbo/super charging, or by clever inlet manifold design.

If a turbo/super charger isn't actively spinning, then it does act as a restriction. That's what turbo lag is....

...and if anyones got a better explanation or rebuttal....

Just thought of a different example: If you've got a syringe, and you stick the end into a glass of water, and pull back the plunger - are you sucking the water in - or is it being pushed in? If it was being pushed - then the plunger (or piston) would move back on it's own... Surely?

[moT]

maybee the weight of air is more than the ammount of suction caused by the cylinder????? thats why its pushed in instead of sucked in i dont really know

[jonbuoy]

The engine would be sucking in a gulp of compressed air?

[Mikkel]

90% 450 pts.

Electrical diagrams are not truly universal so I mixed up load and fuse...
Some of the questions are highly imprecise. E.g. a naturally aspirated engine works by "suction" - but that pressure differential is only there because the atmospheric pressure is there to push the air in... The distinction is artificial and irrelevant at best.

Guess that it isn't minded for scientific personel in the first place

[Hoon]

Grr 96% - got the balloon one and the "compressed air heats up/cools down" one wrong.

Quite an interesting mix of questions. Most can be answered with IQ but some require a bit of knowledge/experience (i.e. Electrical, pulleys, fluid dynamics).

The piston sucks question is a tricky one though. Aren't likely to get this one right unless you know a bit of physics.

[Hoon]

...and there's a pulley question where they reckon there's NO difference between a straight lift (no pully - lifting directly upwards) and using a single pulley - pulling at either 90 degrees from pulley-load or 180 degrees...

Yeah thats another trick question. I immediately clicked downwards would be easier but when I looked closer at the diagram I couldn't explain why. Then I thought about it and realized that the only reason it's easier (in real life) is because you are also using your bodyweight to help pull, but the question isn't asking this.