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Default Brain cells needed - 1955 test

On 26/05/17 05:48, Bill Wright wrote:
On 25/05/2017 22:08, Tim+ wrote:
Bill Wright Wrote in message:
On 25/05/2017 19:16, misterroy wrote:
found this test lurking in the filing cabinet at work, some of the
questions might need a bit more context.

https://drive.google.com/file/d/0B_U...ew?usp=sharing


Is the gate question a trick? H has the brace the wrong way round.

Bill


Nope. A piece of wood like that will work in tension or
compression. If you were to use a diagonal wire it would only
work one way.

Tim

It isn't the wood, it's the joints. The brace is effectively wedged
between the rails. If it's the wrong way round the joints will pull out.
This is utterly basic.


No, Bill. the joints are tenoned and pinned . They cant pull out.

This is utterly basic.


--
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that the dunces are all in confederacy against him."

Jonathan Swift.
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On 26/05/17 08:55, Robin wrote:
On 25/05/2017 23:52, John Rumm wrote:
On 25/05/2017 21:34, The Natural Philosopher wrote:
On 25/05/17 21:27, Bill Wright wrote:
On 25/05/2017 19:16, misterroy wrote:
found this test lurking in the filing cabinet at work, some of the
questions might need a bit more context.

https://drive.google.com/file/d/0B_U...ew?usp=sharing




Is the gate question a trick? H has the brace the wrong way round.

Bill
tesnd to work either way.

There were more than one question however where there seemed to be
insufficient information.

The car skid for example.


Also the capstan.


No, I think not the capstan.

The point of a capstan is to allow leverage and the further from the hub
you are the less force is needed for a given action


The butchers hook one as well... depending what you want to achieve -
least load on the supports, then in the middle. Least bending of the
rail, then right at the end.

Least distance to carry the bloody thing


A perfectly valid answer IMHO!



--
"When a true genius appears in the world, you may know him by this sign,
that the dunces are all in confederacy against him."

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On 26/05/2017 09:02, John Rumm wrote:

Is the gate question a trick? H has the brace the wrong way round.

Bill
tesnd to work either way.


No the force has to be compression on the brace.


It does not *have* to be.


No it's fine to do it the other way if you don't mind the gate pulling
apart when a child swings on it.

Granted that is the traditional way,

Because it works much better. There's a reason for most traditions.

but it
will also work in tension if its well fixed.


How would you do that? Very difficult to get the same strength as doing
it the correct way would.

What is required to prevent
racking of the gate is a triangulated cross member. Having it in
compression works well since it can be notched into the other timbers
and will hence work and stay put even without much in the way of
fixings. In tension it relies more heavily on the fixings, but will
still work.


If it relies more heavily on the fixings it's not as good a design. If
extra stress can be avoided it should be.

As has been said though, in the context of the question, where all the
other alternatives simply had variations on right angle joints and no
brace, its the only clear correct answer.


It's the correct answer but it shows that the author has no idea about
basic joinery techniques.

Bill

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On 26/05/2017 10:35, Roger Hayter wrote:

It isn't the wood, it's the joints. The brace is effectively wedged
between the rails. If it's the wrong way round the joints will pull out.
This is utterly basic.

Bill

Agreed, but until the joints do pull out it is going to do better than
the unbraced ones. They didn't ask if they were sensible designs!



No, it just shows that the author was an ignoramus. I bet he didn't do
woodwork at school.

Bill

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On 26/05/2017 11:29, Rod Speed wrote:


"Bill Wright" wrote in message
news
On 25/05/2017 19:16, misterroy wrote:
found this test lurking in the filing cabinet at work, some of the
questions might need a bit more context.

https://drive.google.com/file/d/0B_U...ew?usp=sharing


A lot of them don't have one definite answer.


Only for those who dont have a clue about the basics.


No, the problem is that if you do have a clue you become aware of the
ambiguities.

Bill


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On 26/05/2017 11:35, Nick wrote:
On 26/05/2017 10:34, Tim Streater wrote:

He ought to be getting that from his Physics classes - friction,
rolling balls down inclined planes, etc.


It was a while ago. I'll ask him but I suspect seeing an experiment
demonstrated once is the same as having personally tried it and got it
wrong many times. For instance the tent peg question.


Another question with no unconditionally correct answer. It would depend
partly on the ground conditions, as anyone who has done a lot of tenting
would know full well.

bill
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On 26/05/2017 13:40, Robin wrote:
On 26/05/2017 12:35, Clive George wrote:
On 26/05/2017 08:55, Robin wrote:
There were more than one question however where there seemed to be
insufficient information.

The car skid for example.

Also the capstan.


The one with the weight hanging off rope at the top of the well? There's
enough information there.


I had in mind the nautical capstan with 4 men and "Which man would have
to work hardest to turn the capstan alone?" ISTM "hardest" is ambiguous
between (a) the force exerted (highest for shortest lever), (b) the
energy required per unit time (ditto if they walk at the same speed -
linear not angular - when walking alone), and (c) the energy required
per revolution (same for all).


Ah, right, fair enough.


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"Bill Wright" wrote in message
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As has been said though, in the context of the question, where all the
other alternatives simply had variations on right angle joints and no
brace, its the only clear correct answer.


It's the correct answer but it shows that the author has no idea about
basic joinery techniques.


No, all it is saying is that the one with the diagonal bar is much better
than any of the other ones in the question, not that it is the *best*
solution. Providing the cross-bar is securely fastened (eg screws or bolts)
to the vertical and/or horizontal bars, it will resist the tendency for the
rectangle to bend out of shape into a parallelogram. But it places a lot
more reliance on the fixings that if the cross-bar was in compression rather
than tension.

Ideally the question should have shown a couple of rectangular gates, plus
one with a compression bar and one with a tension bar. That would have
tested people's knowledge even better.

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On 26/05/2017 12:17, NY wrote:

A bit of experience with Meccano would help a great deal, to understand
the importance of diagonal cross-bracing of a rectangular shape (eg the
gate in one of the questions) or to understand meshing of a train of
gears. Sadly modern children don't seem to "play" with Meccano any more.
I use the word "play" in its widest sense to mean build things and work
out by trial and error what is good and what is bad and how to improve
what is bad.


You are preaching to the converted. I loved my Meccano. I would do
anything for more, I longed for the motor with gears etc.

I bought my son kits that went unopened. He just wasn't interested.

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It happens that Bill Wright formulated :
No, the problem is that if you do have a clue you become aware of the
ambiguities.


Exactly! Some of you guys are over thinking the possible answers and
these questions were intended for a 12 to 14 year old student who would
not think too deeply for the answer.


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On 26/05/2017 15:23, Harry Bloomfield wrote:
It happens that Bill Wright formulated :
No, the problem is that if you do have a clue you become aware of the
ambiguities.


Exactly! Some of you guys are over thinking the possible answers and
these questions were intended for a 12 to 14 year old student who would
not think too deeply for the answer.


I used to find this type of question confusing, when I was 12 to 14.

I found life became much easier at university, doing a maths course
where they actually took the trouble be more precise.
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On 2017-05-26 10:12, Nick wrote:

However is is interesting as it is a very practical test of engineering
mechanics. Practical experience really helps.

When helping my son with mathematical mechanics problems I was surprised
how little practical experience/intuition he had. He had to learn
everything as theory, book learning. For today's computer generation of
children a little more practical teaching in school would be a good
thing but perhaps it is too expensive


In school? I learnt this sort of stuff in my own time, playing with Meccano.


--
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news(a)thenyes.org.uk
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On 26/05/2017 14:04, Bill Wright wrote:
On 26/05/2017 09:02, John Rumm wrote:

Is the gate question a trick? H has the brace the wrong way round.

Bill
tesnd to work either way.

No the force has to be compression on the brace.


It does not *have* to be.


No it's fine to do it the other way if you don't mind the gate pulling
apart when a child swings on it.


It won't necessarily anyway. You also seem to be ignoring the point that
when done the "proper" way it still places the top horizontal member in
tension - pulling on its M&T joint at either end. That will also fail if
over stressed and the joint is not either pined / draw bored or wedged /
foxed.




Granted that is the traditional way,

Because it works much better. There's a reason for most traditions.

but it
will also work in tension if its well fixed.


How would you do that? Very difficult to get the same strength as doing
it the correct way would.


Again it depends on the construction. If the diagonal brace is in the
same plane as the existing timbers[1], then its easier to get good
strength in compression. If however its planted on the face of the gate
(as was shown in the picture), then the performance is the same in
either orientation, however you can use a smaller timber if in tension
rather than compression (you don't need the timber to resist buckling),
so you could argue from an engineering PoV that is actually a more
efficient solution.

[1] e.g. like this one I made earlier:

http://wiki.diyfaq.org.uk/index.php/...and_brace_door


What is required to prevent
racking of the gate is a triangulated cross member. Having it in
compression works well since it can be notched into the other timbers
and will hence work and stay put even without much in the way of
fixings. In tension it relies more heavily on the fixings, but will
still work.


If it relies more heavily on the fixings it's not as good a design. If
extra stress can be avoided it should be.

As has been said though, in the context of the question, where all the
other alternatives simply had variations on right angle joints and no
brace, its the only clear correct answer.


It's the correct answer but it shows that the author has no idea about
basic joinery techniques.


Its a mechanics test, not carpentry ;-)




--
Cheers,

John.

/================================================== ===============\
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|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/
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On 26/05/2017 15:01, Nick wrote:
On 26/05/2017 12:17, NY wrote:

A bit of experience with Meccano would help a great deal, to
understand the importance of diagonal cross-bracing of a rectangular
shape (eg the gate in one of the questions) or to understand meshing
of a train of gears. Sadly modern children don't seem to "play" with
Meccano any more. I use the word "play" in its widest sense to mean
build things and work out by trial and error what is good and what is
bad and how to improve what is bad.


You are preaching to the converted. I loved my Meccano. I would do
anything for more, I longed for the motor with gears etc.

I bought my son kits that went unopened. He just wasn't interested.


Hmm same here...


--
Cheers,

John.

/================================================== ===============\
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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/
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On Friday, 26 May 2017 18:06:47 UTC+1, John Rumm wrote:
It's the correct answer but it shows that the author has no idea about
basic joinery techniques.

Its a mechanics test, not carpentry ;-)


Isn't mechanics just theoretical carpentry though?

With harder sums but less likely to lose a finger.

Owain



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"NY" wrote in message
news
"Nick" wrote in message
news
On 25/05/2017 19:16, misterroy wrote:
found this test lurking in the filing cabinet at work, some of the
questions might need a bit more context.

https://drive.google.com/file/d/0B_U...ew?usp=sharing

As others have said the test is poorly constructed. A few questions one
has to guess what is wanted.

However is is interesting as it is a very practical test of engineering
mechanics. Practical experience really helps.

When helping my son with mathematical mechanics problems I was surprised
how little practical experience/intuition he had. He had to learn
everything as theory, book learning. For today's computer generation of
children a little more practical teaching in school would be a good thing
but perhaps it is too expensive


A bit of experience with Meccano would help a great deal, to understand
the importance of diagonal cross-bracing of a rectangular shape (eg the
gate in one of the questions) or to understand meshing of a train of
gears. Sadly modern children don't seem to "play" with Meccano any more. I
use the word "play" in its widest sense to mean build things and work out
by trial and error what is good and what is bad and how to improve what is
bad.

The questions that I need to think about are the tension/compression
forces in various struts on lattice structures, and which will be
largest/smallest. I did a bit of mech eng on my elec eng course, but I
don't know as much or know the rigorous analysis techniques that a civil
eng would know.


The test is sposed to pick those with mechanical ability,
not which have had training/education in that area.

I always found with my dad that I could just look at stuff
and decide that it was going to work and not fail and
that he couldnt. Nothing to do with training/education.

I also manage to reassemble a push bike epicyclic gearbox
after one of my neighbours kids showed up with a box full
of parts after he had pulled it to bits and couldnt work out
how to get it back together again. I only had a rough idea
about how they worked and did that using the wear marks.

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"Robin" wrote in message
...
On 26/05/2017 12:35, Clive George wrote:
On 26/05/2017 08:55, Robin wrote:
There were more than one question however where there seemed to be
insufficient information.

The car skid for example.

Also the capstan.


The one with the weight hanging off rope at the top of the well? There's
enough information there.


I had in mind the nautical capstan with 4 men and "Which man would have to
work hardest to turn the capstan alone?" ISTM "hardest" is ambiguous
between (a) the force exerted (highest for shortest lever),


Yes, thats the obvious answer.

(b) the energy required per unit time (ditto if they walk at the same
speed - linear not angular - when walking alone),


Thats not working harder.

and (c) the energy required per revolution (same for all).



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"Bill Wright" wrote in message
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On 26/05/2017 11:29, Rod Speed wrote:


"Bill Wright" wrote in message
news
On 25/05/2017 19:16, misterroy wrote:
found this test lurking in the filing cabinet at work, some of the
questions might need a bit more context.

https://drive.google.com/file/d/0B_U...ew?usp=sharing


A lot of them don't have one definite answer.


Only for those who dont have a clue about the basics.


No, the problem is that if you do have a clue you become aware of the
ambiguities.


Not with A LOT OF THEM, just with a couple of them.

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"Bill Wright" wrote in message
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On 26/05/2017 11:35, Nick wrote:
On 26/05/2017 10:34, Tim Streater wrote:

He ought to be getting that from his Physics classes - friction,
rolling balls down inclined planes, etc.


It was a while ago. I'll ask him but I suspect seeing an experiment
demonstrated once is the same as having personally tried it and got it
wrong many times. For instance the tent peg question.


Another question with no unconditionally correct answer. It would depend
partly on the ground conditions, as anyone who has done a lot of tenting
would know full well.


Yes, thats another rather poor question. But if you assume
he meant hopeless ground for tent pegs, its not that bad.



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wrote
John Rumm wrote


It's the correct answer but it shows that the author
has no idea about basic joinery techniques.


Its a mechanics test, not carpentry ;-)


Isn't mechanics just theoretical carpentry though?


Nope, much mechanics like leverage has nothing to with carpentry.

In spades with which of the things are easiest to turn over.



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On 26/05/2017 14:26, NY wrote:
"Bill Wright" wrote in message
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As has been said though, in the context of the question, where all the
other alternatives simply had variations on right angle joints and no
brace, its the only clear correct answer.


It's the correct answer but it shows that the author has no idea about
basic joinery techniques.


No, all it is saying is that the one with the diagonal bar is much
better than any of the other ones in the question,


But why present an answer that relies on an incorrect depiction when it
could be a correct one? The only possible reason is that the author must
have no idea about how to make a gate and never bothered to ask a
joiner. That's very sloppy.

Since the thing is supposed to be about engineering principles and not
the behaviour of wood the correct answer will be the gate that used the
brace to form a triangle for strength, and nothing to do with the wood
warping. On that basis the gate as shown is just plain wrong.

It doesn't mention that the gate is made of wood, so the 'wood' argument
clearly wrong.

Bill

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On 26/05/2017 18:06, John Rumm wrote:

[1] e.g. like this one I made earlier:

http://wiki.diyfaq.org.uk/index.php/...and_brace_door


In which the braces are the correct way!

Bill
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On Fri, 26 May 2017 18:17:46 +0100, John Rumm wrote:

You are preaching to the converted. I loved my Meccano. I would do
anything for more, I longed for the motor with gears etc.

I bought my son kits that went unopened. He just wasn't

interested.

Hmm same here...


Yep, Lego NXT here. What could be better these days, building things,
with servo motors, sensors, all easyly programable. A few of the
things in the book where built but no playing as in "what can I make
this stuff do".

Yet the same lad has "built" an 8 bit adder with input/output
registers in Minecraft from scratch. Started by looking up circuits
for adders and went from there, I think he still works on building a
8 bit microprocessor from time to time. Builds all manner of space
ships in Kerbal Space Program, so the imgination and "what if" is
there. I guess the reward feedback loop is much shorter, want to
change something? click, click, drag, click, test. Rather than 15
minutes or longer deconstructing and reconstructing...

--
Cheers
Dave.



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On 26/05/2017 13:59, The Natural Philosopher wrote:


No the force has to be compression on the brace.

Bill

No Bill, It does not


Contradiction is not an argument.

Bill

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On 26/05/2017 14:00, The Natural Philosopher wrote:

No, Bill. the joints are tenoned and pinned . They cant pull out.

This is utterly basic.


A properly made gate or door doesn't need to stress the joints (which
are much weaker than the timber members) because the brace pushes up
against the cross members.

If you rely on pins the first bit of rot and the thing falls apart.

Bill


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On 26/05/2017 15:36, The Peeler wrote:

Only for those who don’t have a clue about the basics.


LOL! You don't have a clue at all about how you keep coming across, eh, you
cantankerous senile old fart?

Those who resort to personal abuse demonstrate
(a) that they don't have a valid argument
(b) that they are immature
(c) that they don't wipe their bums properly.

(I might have made one of those up)

Bill
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"Bill Wright" wrote in message
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On 26/05/2017 13:59, The Natural Philosopher wrote:


No the force has to be compression on the brace.

Bill

No Bill, It does not


Contradiction is not an argument.


But it is a statement of fact in this case.

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On Fri, 26 May 2017 22:19:58 +1000, FMurtz
wrote:

Graham. wrote:
On Thu, 25 May 2017 11:16:16 -0700 (PDT), misterroy
wrote:

found this test lurking in the filing cabinet at work, some of the questions might need a bit more context.

https://drive.google.com/file/d/0B_U...ew?usp=sharing


Would I be disqualified for putting a mark on the line provided,
rather than crossing out the letter corresponding to the correct
answer as instructed?


You do not need to you can see where the mark is rubbed out.


I hadn't noticed that. Still, it's a strange implementation of
"crossing out"
--

Graham.
%Profound_observation%
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On 26/05/17 21:24, Dave Liquorice wrote:
On Fri, 26 May 2017 18:17:46 +0100, John Rumm wrote:

You are preaching to the converted. I loved my Meccano. I would do
anything for more, I longed for the motor with gears etc.

I bought my son kits that went unopened. He just wasn't

interested.

Hmm same here...


Yep, Lego NXT here. What could be better these days, building things,
with servo motors, sensors, all easyly programable. A few of the
things in the book where built but no playing as in "what can I make
this stuff do".

Yet the same lad has "built" an 8 bit adder with input/output
registers in Minecraft from scratch. Started by looking up circuits
for adders and went from there, I think he still works on building a
8 bit microprocessor from time to time. Builds all manner of space
ships in Kerbal Space Program, so the imgination and "what if" is
there. I guess the reward feedback loop is much shorter, want to
change something? click, click, drag, click, test. Rather than 15
minutes or longer deconstructing and reconstructing...

Nowt wrong in that.

When I were a lad it was meccano and model planes. Then it was soldering
transistors together which became my first career. Programming
mainframes == too bloody slow

Then micros arrived with screens and keyboards and computing was now
minutes, not days.

And computers cost hundreds, not millions

Today you wouldn't make something out of meccano. You would solid model
it and get it 3D printed. Or laser cut.




--
"The great thing about Glasgow is that if there's a nuclear attack it'll
look exactly the same afterwards."

Billy Connolly
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On 26/05/17 21:25, Bill Wright wrote:
On 26/05/2017 13:59, The Natural Philosopher wrote:


No the force has to be compression on the brace.

Bill

No Bill, It does not


Contradiction is not an argument.


Dont be silly


Bill



--
Ideas are more powerful than guns. We would not let our enemies have
guns, why should we let them have ideas?

Josef Stalin


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On 26/05/17 21:27, Bill Wright wrote:
On 26/05/2017 14:00, The Natural Philosopher wrote:

No, Bill. the joints are tenoned and pinned . They cant pull out.

This is utterly basic.


A properly made gate or door doesn't need to stress the joints (which
are much weaker than the timber members) because the brace pushes up
against the cross members.

If you rely on pins the first bit of rot and the thing falls apart.

Bill


No structural truss exists without some members being in tension

In the case of 'your' gate design its the top horizontal member.Ergo the
joint to the upright at the hinge post will fail instead


--
Ideas are more powerful than guns. We would not let our enemies have
guns, why should we let them have ideas?

Josef Stalin
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On 26/05/17 21:31, Bill Wright wrote:
On 26/05/2017 15:36, The Peeler wrote:

Only for those who dont have a clue about the basics.


LOL! You don't have a clue at all about how you keep coming across,
eh, you
cantankerous senile old fart?

Those who resort to personal abuse demonstrate
(a) that they don't have a valid argument
(b) that they are immature
(c) that they don't wipe their bums properly.

(I might have made one of those up)

Bill

Nevertheless Bill, you are suffering from a common complaint,. you think
that the little you do know is all there is to know. Those of us who
have done this for a living and studied it at university know it aint
that simple.

The only time a structure is entirely in compression is the case of
masonry. The arch is the only solution to a structure that can span a
gap and still be only under compression.

Wood however is much better in tension than compression. Slender spars
can buckle under compression (if you have studied Euler's slender column
theory, the reasons are all there) and for that reason trees being
naturally slender things the use of timber in tension is the art of
structural carpentry.

The solution to joints in tension is pinning. And notching. And various
other techniques

http://www.basiccarpentrytechniques....oints%202.html

In essence the truss is a way to use slender spars that are short
enough between joints to not suffer Euler buckling when in compression.

A triangulated gate is just another truss. Some joints wioll be in
tension, some in compression.

If you cant make a joint that will take tension, you are not a carpenter

Of course these days you slap a metal plate over and bolt through, otr
just have a metal plate with teeth on pressed into the joint... but
there are proper ways not involving steel



--
€œit should be clear by now to everyone that activist environmentalism
(or environmental activism) is becoming a general ideology about humans,
about their freedom, about the relationship between the individual and
the state, and about the manipulation of people under the guise of a
'noble' idea. It is not an honest pursuit of 'sustainable development,'
a matter of elementary environmental protection, or a search for
rational mechanisms designed to achieve a healthy environment. Yet
things do occur that make you shake your head and remind yourself that
you live neither in Joseph Stalins Communist era, nor in the Orwellian
utopia of 1984.€

Vaclav Klaus
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Default Brain cells needed - 1955 test

On Friday, 26 May 2017 21:24:53 UTC+1, Dave Liquorice wrote:
Rather than 15
minutes or longer deconstructing and reconstructing...


It was the deconstructing part that put me off meccano.

Owain

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Default Brain cells needed - 1955 test

NY wrote:

"Clive George" wrote in message
o.uk...
On 26/05/2017 08:55, Robin wrote:
There were more than one question however where there seemed to be
insufficient information.

The car skid for example.

Also the capstan.


The one with the weight hanging off rope at the top of the well? There's
enough information there.



Here are my answers with reasoning:

snip
33. S closest to centre so he's exerting least turning moment to overcome
whatever the capstan is turning
34. X resultant force is midway between directions of pushing forces
35. smallest radius of curvature so greatest (mv^2)/r centripetal force
(assuming all cars doing same linear speed)
36. H
37. one ball hits the group of four so one ball leaves group (as for
Newton's Cradle)
38. all equal
39. opposite, unevenly (won't jam because ends of rod are 180 deg out of
phase so no vertical component to motion)

I'm open to argument/correction on some of them!


33 He is doing the same amount of work (force X distance moved)
wherever on the capstan he pushes. If they meant force they should
have said so.

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Rod Speed wrote:

"Robin" wrote in message
...
On 26/05/2017 12:35, Clive George wrote:
On 26/05/2017 08:55, Robin wrote:
There were more than one question however where there seemed to be
insufficient information.

The car skid for example.

Also the capstan.

The one with the weight hanging off rope at the top of the well? There's
enough information there.


I had in mind the nautical capstan with 4 men and "Which man would have to
work hardest to turn the capstan alone?" ISTM "hardest" is ambiguous
between (a) the force exerted (highest for shortest lever),


Yes, that's the obvious answer.

(b) the energy required per unit time (ditto if they walk at the same
speed - linear not angular - when walking alone),


That's not working harder.

and (c) the energy required per revolution (same for all).



If you assume the capstan has to be pushed with a constant rotational
speed then c) is right. If the man has a constant force available he
is doing more work the faster he walks so the furthest out one is the
answer. But unless the capstan has to be pushed at a constant speed it
is a bit hard to see any sensible answer for work done.



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Clive George wrote:

On 26/05/2017 09:02, John Rumm wrote:
On 26/05/2017 05:40, Bill Wright wrote:
On 25/05/2017 21:34, The Natural Philosopher wrote:
On 25/05/17 21:27, Bill Wright wrote:
On 25/05/2017 19:16, misterroy wrote:
found this test lurking in the filing cabinet at work, some of the
questions might need a bit more context.


https://drive.google.com/file/d/0B_U...N1c0U/view?usp
=sharing




Is the gate question a trick? H has the brace the wrong way round.

Bill
tesnd to work either way.

No the force has to be compression on the brace.


It does not *have* to be. Granted that is the traditional way, but it
will also work in tension if its well fixed. What is required to prevent
racking of the gate is a triangulated cross member. Having it in
compression works well since it can be notched into the other timbers
and will hence work and stay put even without much in the way of
fixings. In tension it relies more heavily on the fixings, but will
still work.

As has been said though, in the context of the question, where all the
other alternatives simply had variations on right angle joints and no
brace, its the only clear correct answer.


The joints were clearly pins able to take compression or tension as well.


But too near the end of the strut to last long in tension without
splitting the wood. Agree with you re the answer.

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John Rumm wrote:

On 26/05/2017 14:04, Bill Wright wrote:
On 26/05/2017 09:02, John Rumm wrote:

Is the gate question a trick? H has the brace the wrong way round.

Bill
tesnd to work either way.

No the force has to be compression on the brace.

It does not *have* to be.


No it's fine to do it the other way if you don't mind the gate pulling
apart when a child swings on it.


It won't necessarily anyway. You also seem to be ignoring the point that
when done the "proper" way it still places the top horizontal member in
tension - pulling on its M&T joint at either end. That will also fail if
over stressed and the joint is not either pined / draw bored or wedged /
foxed.




Granted that is the traditional way,

Because it works much better. There's a reason for most traditions.

but it
will also work in tension if its well fixed.


How would you do that? Very difficult to get the same strength as doing
it the correct way would.


Again it depends on the construction. If the diagonal brace is in the
same plane as the existing timbers[1], then its easier to get good
strength in compression. If however its planted on the face of the gate
(as was shown in the picture), then the performance is the same in
either orientation, however you can use a smaller timber if in tension
rather than compression (you don't need the timber to resist buckling),
so you could argue from an engineering PoV that is actually a more
efficient solution.

[1] e.g. like this one I made earlier:

http://wiki.diyfaq.org.uk/index.php/...and_brace_door


I've made an internal ledged and braced door and then changed my mind
about the hinge side at a late stage. It is so over-engineered I am
not worried about the danger of it failing, just the embarassment of
anyone seeing it and knowing I made it!



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On 26/05/2017 23:16, Roger Hayter wrote:
John Rumm wrote:

On 26/05/2017 14:04, Bill Wright wrote:
On 26/05/2017 09:02, John Rumm wrote:

Is the gate question a trick? H has the brace the wrong way round.

Bill
tesnd to work either way.

No the force has to be compression on the brace.

It does not *have* to be.

No it's fine to do it the other way if you don't mind the gate pulling
apart when a child swings on it.


It won't necessarily anyway. You also seem to be ignoring the point that
when done the "proper" way it still places the top horizontal member in
tension - pulling on its M&T joint at either end. That will also fail if
over stressed and the joint is not either pined / draw bored or wedged /
foxed.




Granted that is the traditional way,

Because it works much better. There's a reason for most traditions.

but it
will also work in tension if its well fixed.

How would you do that? Very difficult to get the same strength as doing
it the correct way would.


Again it depends on the construction. If the diagonal brace is in the
same plane as the existing timbers[1], then its easier to get good
strength in compression. If however its planted on the face of the gate
(as was shown in the picture), then the performance is the same in
either orientation, however you can use a smaller timber if in tension
rather than compression (you don't need the timber to resist buckling),
so you could argue from an engineering PoV that is actually a more
efficient solution.

[1] e.g. like this one I made earlier:

http://wiki.diyfaq.org.uk/index.php/...and_brace_door


I've made an internal ledged and braced door and then changed my mind
about the hinge side at a late stage. It is so over-engineered I am
not worried about the danger of it failing, just the embarassment of
anyone seeing it and knowing I made it!


I made a picket gate once (on saloon hinges, to keep the dog out of the
kitchen!) Since the brace was planted onto the face of the pickets
rather than built into the plane of the other timbers it made no
difference which way it went. I was content to let SWMBO choose after
construction and needless to say it ended up in tension.


--
Cheers,

John.

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On 26/05/2017 21:24, Bill Wright wrote:
On 26/05/2017 18:06, John Rumm wrote:

[1] e.g. like this one I made earlier:

http://wiki.diyfaq.org.uk/index.php/...and_brace_door


In which the braces are the correct way!


Indeed. On that type of construction, it is the "right" way. For the
type pictured in the mechanics paper, it does not matter.


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Cheers,

John.

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On 26/05/2017 21:19, Bill Wright wrote:
On 26/05/2017 14:26, NY wrote:
"Bill Wright" wrote in message
news
As has been said though, in the context of the question, where all the
other alternatives simply had variations on right angle joints and no
brace, its the only clear correct answer.

It's the correct answer but it shows that the author has no idea about
basic joinery techniques.


No, all it is saying is that the one with the diagonal bar is much
better than any of the other ones in the question,


But why present an answer that relies on an incorrect depiction when it
could be a correct one? The only possible reason is that the author must
have no idea about how to make a gate and never bothered to ask a
joiner. That's very sloppy.

Since the thing is supposed to be about engineering principles and not
the behaviour of wood the correct answer will be the gate that used the
brace to form a triangle for strength, and nothing to do with the wood
warping. On that basis the gate as shown is just plain wrong.

It doesn't mention that the gate is made of wood, so the 'wood' argument
clearly wrong.


If it were steel, then it would be better in tension - steel is stronger
that way, and not going to buckle.


--
Cheers,

John.

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