How good is YOUR mechanical knowledge? [Archive]

sAsLEX

24th October 2007, 04:12

bungbung

24th October 2007, 08:23

96%, need to pay more attention

Fooman

24th October 2007, 08:38

Question 48 the answer is wrong!

NA engines. Air is sucked into the engine by the vacuum created as the piston descends I am sure of it. If I covered the intake of the lawn mower with my hand it would suck my palm until it starved, no kill switch you see.

90% for an elect engineer who got one of the battery questions wrong by not payinng enough attention!

No such thing as sucking - there is a pressure differential between the lower pressure cylinder and the higher pressure atmosphere. The fluid moves from a volume of high pressure to low pressure to minimize the energy state of the system. The atmospheric pressure forces your hand over the lawn mower intake - the "suck" you feel is the effect of the higher pressure inside your skin compared to the pressure in the intake.

Think of water in a dam - does it get sucked down the penstocks, or does it get pushed down by the higher pressure/head due to the height of the water.

Cheers,
FM

steveb64

24th October 2007, 08:41

Steam

24th October 2007, 08:47

No such thing as sucking

Yes there is. It is a subjective term which depends on which side of the pressure differential you are standing. If the air is going into the hole that's sucking. If the air is coming out of the hole that's pushing.

Winter

24th October 2007, 09:06

76%. :-(

I'm going to take it again in a couple of days to see if I absorbed any of it.

sAsLEX

24th October 2007, 09:11

No such thing as sucking -

When the piston moves from top to bottom, it sucks in a certain amount of air. How much air it can suck in depends on how big around the piston is, and how far it moves when it goes from top to bottom.

You find a reference to back up your story! :girlfight:

Suck, squeeze, bang, blow
Not a sexual maneuver, but rather the common description for how an internal combustion engine works. The basic way all internal combustion engines work is to suck in a mixture of fuel and air, compress it, ignite it either with a spark plug or by self-igntion (in the case of a diesel engine), allow the explosion of combusting gasses to force the piston back down and then expel the exhaust gas.

steveb64

24th October 2007, 09:13

...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... :(

Short of trying to find a pulley in the mass of accumulated crap that's my garage, and using a spring scale to measure... naaahhhh too much work... I thought that even using a single pulley would reduce the work load?

hazard02

24th October 2007, 09:28

88%- Not bad for half a degree in robotic engineering. I'd be set if I was studying mechanical engineering!

k14

24th October 2007, 09:32

...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... :(
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.

imdying

24th October 2007, 09:40

sAsLEX

24th October 2007, 09:42

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

Really? not from this elec engineer

deanohit

24th October 2007, 09:47

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

sAsLEX

24th October 2007, 09:50

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

24th October 2007, 09:50

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

steveb64

24th October 2007, 10:12

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! :no:

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

24th October 2007, 10:14

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. :2thumbsup

steveb64

24th October 2007, 10:20

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.:whistle: I knew multi pulleys changed leverage ratios - just not singles... :beer:

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

imdying

24th October 2007, 10:25

Errm - the question was relating to a "Normally Aspirated" engine.No shit... just like your reply, only the first sentence was directly related...

steveb64

24th October 2007, 10:26

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

Am I the only one who has seen this

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

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

moT

24th October 2007, 10:36

yeah 66% i think i need a mechanic

steveb64

24th October 2007, 10:53

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

:Oi: 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.... :cool:

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

24th October 2007, 10:57

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

24th October 2007, 12:23

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

Mikkel

24th October 2007, 12:53

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

24th October 2007, 14:18

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

24th October 2007, 14:25

...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.

devnull

24th October 2007, 14:31

92% :niceone:

Could have a second career if I ever get tired of building networks :2thumbsup

Brett

24th October 2007, 15:00

78% but I rushed it. Will take some time when I have some and see how I can do.

MacD

24th October 2007, 18:26

490 points, 98%

I always wanted to be an engineer... ;)

The piston question is similar to the usual arguement about centrifugal force, it all depends on your point of view, but the generally accepted scientific/engineering principle is that the air flows into the cylinder due to the pressure differential, ie. higher atmospheric pressure "pushes" the air in. Hence the use of turbos to incease manifold pressure.

boostin

24th October 2007, 19:35

80% wow amazing

Mom

24th October 2007, 19:58

I failed........hardly surprising, but wow I got 62%!!!!!!!!!!!!!!

I rock!

JeremyW

24th October 2007, 20:36

Sweet 88%. Yea the engine sucking one got me too but it does make sense when you think of it... A vacuum is a pressure lower than atmospheric and hence the atmosphere 'pushes' the air in.

Sanx

24th October 2007, 21:45

94%, and I'm not a mechanic. I'm an out-of-work IT contractor. Perhaps I should think about a career-change.

Except they forgot the main mechnics question:

Q51. You disassemble and then reassemble a complicated mechanical object. Expressed as a percentage of the toal number of discrete components in the object, how many is it acceptable to have left lying on the floor when you've finished.

a) 0%
b) 5%
c) 10%
d) 50%. She'll be right, mate!

Conquiztador

25th October 2007, 01:31

94%. That was interesting.

Got the sucking wrong in the motor. Sucks!

Got the fan direction wrong. Was thinking to deeply here...

Also the pressure of the water in the hose with 2 pipes up. Did not think there was gonna be any water going up in the second pipe.

Ah well.

Bass

25th October 2007, 11:38

Ocean1

25th October 2007, 11:45

100%

Well bugger me!
Perhaps I should become an engineer.

Hang on a sec............I already am.

That might have something to do with it then.......home town advantage.

I guess it's gotta be useful sometimes

Should bloody well think so, it's a test for Ford mechanics.

*Silently glosses over the fact that he missed one...*

judecatmad

25th October 2007, 12:02

74%.

Not bad for an Insurance Underwriter (who completely failed the first year of the Physics degree she started before defecting to Chemistry!)

:D

Fooman

25th October 2007, 13:44

You find a reference to back up your story! :girlfight:

You've made me open up a book for the first time in about 10 years:

B.S. Massey, Mechanics of Fluids, 6th Ed, 1989 Chapman & Hall

Chapter 13, Unsteady Flow :drinkup:

See the definition of inertia pressure.

(First few pages of Massey attached)

Cheers,
FM

steveb64

25th October 2007, 14:32

You've made me open up a book for the first time in about 10 years:

B.S. Massey, Mechanics of Fluids, 6th Ed, 1989 Chapman & Hall

Chapter 13, Unsteady Flow :drinkup:

See the definition of inertia pressure.

(First few pages of Massey attached)

Cheers,
FM

You win. :argh:

Also got this off forum (GSresources) I originally got the link from : A Vacuum DOES NOT pull air into the cylinder. The atmospheric pressure just rushes in to FILL that vacuum. :first: :beer:

Bass

25th October 2007, 15:48

Should bloody well think so, it's a test for Ford mechanics.

And diesel mechanics at that - so what were the electrical questions in aid of?
Does this mean that Ford has heard about electricity?

Ocean1

25th October 2007, 16:31

And diesel mechanics at that - so what were the electrical questions in aid of?
Does this mean that Ford has heard about electricity?

Heard about it, and want no truck with it, or any of those other new fangled ideas.

Just be greatful they haven't heard of motorcycles...

Edbear

25th October 2007, 17:11

86%, but you only got one shot at the questions, so I couldn't change an answer when I realised I'd got one battery question wrong!:2guns:

Still, I reckon I should have done better. The atmospheric question is as old as the internal combustion engine...:whistle:

raster

25th October 2007, 18:28

90%, 450 Points, not too bad, got the balloon and sucky questions wrong, if you want to see progress, click icon botton left, show/hide TOC.

Slingshot

25th October 2007, 19:16

No such thing as sucking

You're right, the pressure is lower in my wife's mouth compared to the pressure around my cock.

94%, and I'm not a mechanic. I'm an out-of-work IT contractor. Perhaps I should think about a career-change.

Except they forgot the main mechnics question:

Q51. You disassemble and then reassemble a complicated mechanical object. Expressed as a percentage of the toal number of discrete components in the object, how many is it acceptable to have left lying on the floor when you've finished.

a) 0%
b) 5%
c) 10%
d) 50%. She'll be right, mate!

Commonly known as hedge bolts...cause you throw them in the hedge.

I can't understand how I got the attached one wrong:

Ocean1

25th October 2007, 19:58

I can't understand how I got the attached one wrong:

With both switches closed the middle bulb is by-passed by the RH switch, current will flow through the switch rather than the bulb.

skidMark

25th October 2007, 20:31

got to question 20 and realised i had fucked up question 15 or 16 or sumthing..so closed it ... :)

Slingshot

25th October 2007, 20:38

With both switches closed the middle bulb is by-passed by the RH switch, current will flow through the switch rather than the bulb.

I thought it would flow through both the switch and the bulb as the middle bulb and that switch are in parallel.

rwh

25th October 2007, 20:52

I thought it would flow through both the switch and the bulb as the middle bulb and that switch are in parallel.

It will - but so disproportionately in favour of the switch that you won't notice the bulb.

Richard

rwh

25th October 2007, 20:56

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.

I can't see the quiz (no bloody flash for 64-bit yet) but you can gain an advantage with one pulley - fix it to the load, and tie the end of the rope that you're not pulling to the structure above.

Richard

howdamnhard

25th October 2007, 20:58

Electricity always follows the path of least resistance.The switch acts as a short circuit/conductor.:2thumbsup

I thought it would flow through both the switch and the bulb as the middle bulb and that switch are in parallel.

Slingshot

25th October 2007, 21:05

It will - but so disproportionately in favour of the switch that you won't notice the bulb.

Richard

Electricity always follows the path of least resistance.The switch acts as a short circuit/conductor.:2thumbsup

Aha, of course. Like water.

rwh

25th October 2007, 21:20

Electricity always follows the path of least resistance.The switch acts as a short circuit/conductor.:2thumbsup

Inversely proportional to the resistance - which is low, but not zero, for the switch (and wires either side of it).

Richard

howdamnhard

25th October 2007, 21:30

Exactly right.:niceone:

Aha, of course. Like water.

Angusdog

25th October 2007, 21:45

86%. Not bad for a graphic designer...

Questions they should have asked:

If you cross thread a bolt, will it 'get better' by continuing to turn?

If the apparent torque required when tightening a bolt reduces, does that mean you're getting stronger?

Is electricity the work of the devil?

If an electrical component starts to emit smoke, should you go to Repco for a new can for smoke to replace the smoke it's losing?

Do rotary engines suck?

Do scooters travel faster when going with the earth's rotation?

Ocean1

25th October 2007, 22:02

If you cross thread a bolt, will it 'get better' by continuing to turn?

If the apparent torque required when tightening a bolt reduces, does that mean you're getting stronger?

Is electricity the work of the devil?

If an electrical component starts to emit smoke, should you go to Repco for a new can for smoke to replace the smoke it's losing?

Do rotary engines suck?

Do scooters travel faster when going with the earth's rotation?

No.
No.
No.
No.
No.
Yes.

Trouble with yer torque wrench dude?
Standard practice is tighten until it strips and then back it off a quarter turn. :done:

steveb64

25th October 2007, 22:10

Commonly known as hedge bolts...cause you throw them in the hedge.

I can't understand how I got the attached one wrong:

The second switch shorts out the middle bulb. Current takes path of least resistance, so goes thru switch, not bulb...

Errk - just saw ho many others had replied to that... :doh:

Hoon

26th October 2007, 11:21

Do scooters travel faster when going with the earth's rotation?

Yes.

Now I don't know about that?!? Speed in relation to what?

A fixed point on the earth without taking the earths rotation into account then no.

A fixed point in space and taking the earths rotation into account then maybe?

Because if you take the earths rotation into account (1600kph at the equator) then you also have to take into account the fact that the earth is moving around the sun at over 108,000 kph. So the scooter would travel faster on the dark side but slower on the light side.

But then our solar system is also spinning around the galaxy at 900,000kph.

And then our Milky way is moving through the galaxy cluster even faster!

rwh

26th October 2007, 12:14

Now I don't know about that?!? Speed in relation to what?

A fixed point on the earth without taking the earths rotation into account then no.

A fixed point in space and taking the earths rotation into account then maybe?

Because if you take the earths rotation into account (1600kph at the equator) then you also have to take into account the fact that the earth is moving around the sun at over 108,000 kph. So the scooter would travel faster on the dark side but slower on the light side.

But then our solar system is also spinning around the galaxy at 900,000kph.

And then our Milky way is moving through the galaxy cluster even faster!

Therefore all (speeding) tickets should be disputed on the basis that the law is impossible to obey.

Alternatively, when I measure my speed from my own frame of reference, I'm not moving at all, and never have.

Richard

Ocean1

26th October 2007, 13:15

Speed in relation to what?

Wasn't specified. On the basis that there's infinitely more reference points in the universe than that of the road surface immediately under said scooter, (all traveling at vastly higher speed) my answer is overwhelmingly more credible.

Besides:
I don't know about that?!?

:bleh:

Jantar

11th November 2007, 09:37

92%

And I agree with Saslex on the NA engine question. Air is sucked in as the pressure in the cylinder reduces as the piston moves down.

Another one that is open is the one on the venturi effect where water is passed rapidly through a tube with a constriction. If water is passed rapidly then tube B will act as a suction and no water will rise in the tube. That is how a Carb works.

Dave-

11th November 2007, 17:40

72%

cocked up the weights on pullys, 1 or 2 of the electrical questions and some others that I realized only after I'd hit next.

as for the piston (which i got wrong) when the fuel ignites, the exhaust is sucked out and you're left with a vacume, beucase the atmosphear of a vacume is 0 and earths atmosphear is 1 then the air from outside the engine trys to fill this gap.

I didnt realise this until I'd hit next and cbf doing the whole thing again.