| Topic: |
Science > Physics |
| User: |
"" |
| Date: |
04 Feb 2005 10:05:59 AM |
| Object: |
Why does measuring tape bend one way? |
Why does metal measuring tape easily bend one way but not the other?
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| User: "CWatters" |
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| Title: Re: Why does measuring tape bend one way? |
04 Feb 2005 11:59:45 AM |
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<lemo5@optonline.net> wrote in message
news:1107533159.730098.166440@z14g2000cwz.googlegroups.com...
Why does metal measuring tape easily bend one way but not the other?
and before anyone replies that it's due to the curve... _How_ does the curve
give it these properties?
I think it's because the curve makes it easier to _twist_
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| User: "Nick Rouse" |
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| Title: Re: Why does measuring tape bend one way? |
04 Feb 2005 08:15:46 PM |
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"CWatters" <colin.watters@pandoraBOX.be> wrote in message news:<lKOMd.3324$7j5.286768@phobos.telenet-ops.be>...
<lemo5@optonline.net> wrote in message
news:1107533159.730098.166440@z14g2000cwz.googlegroups.com...
Why does metal measuring tape easily bend one way but not the other?
and before anyone replies that it's due to the curve... _How_ does the curve
give it these properties?
I think it's because the curve makes it easier to _twist_
I think it is because the initial bend in the direction that it
normally coils up in tries to put the centre line of the tape
into tension and the edges into compression. Because the
tape is thin compared to the length over which the compressive
force is acting and the edge is unconstrained it very soon
becomes unstable and buckles. I suspect (but can't pin down
exactly why) an outward (flattening) buckle is energetically
more favourable than an inward curling buckle.
In the classical analysis of a column failing under compression
you compare the energy needed to deform the column into a
slight curve with the energy released by the compressive force
moving as the deformation allows the force to move. If the
deformation energy is less than energy released by the compressive
force the deformation continues. Different deformation modes have
different ratios of these two forces and the most energetically
favoured will dominate but nearly all modes tend to show a greater
ratio of released energy to deformation energy the greater the degree
of deformation and conversely the ratio falls to zero for the initial
infinitesimal deformation. This implies that once a column starts to
buckle it will collapse catastrophically but that the initiation of
deformation is dependant on imperfections to take it to the
point at which the deformation starts to grow . The greater the
compressive force the smaller the imperfection that will take the
system to the point where further deformation is energetically
favourable. Generally the simplest modes of deformation involving
the fewest changes in curvature will be the most energetically
favourable. Complex modes with many curve changes will require
a greater compressive force before imperfections bring such modes
to the critical point.
To return to the tape, It takes only a small bending force before imperfections
allow the tape to start flattening and once the tape has started to flatten it
becomes ever easier to flatten it more and easier to bend it in its coiling
direction.
If you try to bend the tape in the opposite direction you are trying to
put the edges in tension and the centre into compression. because the
centre part of the tape is constrained on both sides, the lowest energy mode
of deformation will still be a complex one, probably involving the formation
of a dimple with an S shaped curve in two directions. It will therefore take
a greater bending force before likely imperfections make such deformations
likely
Nick Rouse
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| User: "Edward Green" |
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| Title: Re: Why does measuring tape bend one way? |
10 Feb 2005 06:55:50 PM |
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Nick Rouse wrote:
I think it is because the initial bend in the direction that it
normally coils up in tries to put the centre line of the tape
into tension and the edges into compression. Because the
tape is thin compared to the length over which the compressive
force is acting and the edge is unconstrained it very soon
becomes unstable and buckles. I suspect (but can't pin down
exactly why) an outward (flattening) buckle is energetically
more favourable than an inward curling buckle.
In the classical analysis of a column failing under compression
you compare the energy needed to deform the column into a
slight curve with the energy released by the compressive force
moving as the deformation allows the force to move. If the
deformation energy is less than energy released by the compressive
force the deformation continues. Different deformation modes have
different ratios of these two forces and the most energetically
favoured will dominate but nearly all modes tend to show a greater
ratio of released energy to deformation energy the greater the degree
of deformation and conversely the ratio falls to zero for the initial
infinitesimal deformation. This implies that once a column starts to
buckle it will collapse catastrophically but that the initiation of
deformation is dependant on imperfections to take it to the
point at which the deformation starts to grow . The greater the
compressive force the smaller the imperfection that will take the
system to the point where further deformation is energetically
favourable. Generally the simplest modes of deformation involving
the fewest changes in curvature will be the most energetically
favourable. Complex modes with many curve changes will require
a greater compressive force before imperfections bring such modes
to the critical point.
To return to the tape, It takes only a small bending force before
imperfections
allow the tape to start flattening and once the tape has started to
flatten it
becomes ever easier to flatten it more and easier to bend it in its
coiling
direction.
If you try to bend the tape in the opposite direction you are trying
to
put the edges in tension and the centre into compression. because the
centre part of the tape is constrained on both sides, the lowest
energy mode
of deformation will still be a complex one, probably involving the
formation
of a dimple with an S shaped curve in two directions. It will
therefore take
a greater bending force before likely imperfections make such
deformations
likely
Nick Rouse
I owe you a slight apology. I had previously said that Philip Holman's
reply was the only one which seemed plausible and about on the right
level. I don't know about "on the right level", but your discussion is
very nice, and suggests the tools to take the thing a step beyond
intuition!
Now, to add something, I notice in actual experiment that slowly
bending a length of measuring tape in the hard direction causes a
slight flattening in the area of subsequent buckling, followed by a
sharp snap to the buckled position; slowly releasing the bending moment
eventually causes a snap back to the unbuckled shaped. The system is
bistable (obviously), and exhibits hysterisis.
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| User: "Ken Muldrew" |
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| Title: Re: Why does measuring tape bend one way? |
11 Feb 2005 03:16:35 PM |
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"Edward Green" <spamspamspam3@netzero.com> wrote:
Now, to add something, I notice in actual experiment that slowly
bending a length of measuring tape in the hard direction causes a
slight flattening in the area of subsequent buckling, followed by a
sharp snap to the buckled position; slowly releasing the bending moment
eventually causes a snap back to the unbuckled shaped. The system is
bistable (obviously), and exhibits hysterisis.
You may be interested to know that there is a "jam side down" physical
law with respect to measuring tapes. Every measurement where you are
unable to support the tape easily is just far enough to cause
buckling. There has never been a demonstrated exception to this rule.
Ken Muldrew
kmuldrezw@ucalgazry.ca
(remove all letters after y in the alphabet)
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| User: "Edward Green" |
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| Title: Re: Why does measuring tape bend one way? |
11 Feb 2005 07:53:08 PM |
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Ken Muldrew wrote:
You may be interested to know that there is a "jam side down"
physical
law with respect to measuring tapes. Every measurement where you are
unable to support the tape easily is just far enough to cause
buckling. There has never been a demonstrated exception to this rule.
Interesting. Then perhaps we can devise a kind of "inertialess drive"
by trying to measure the distance to a nearby object with stiffer and
stiffer tapes, causing the object to recede with zero momentum in the
reference frame. Of course it may be objected that the distance to the
object only exists when we measure it, otherwise presumably having an
imaginary value; in this way the sums of squares and hence RMS distance
is enabled to remain constant while the series of lower bounds given by
the buckling lengths of the unsupported tapes grows without bound,
proving that the object is receding on a right circularly polarized
light cone, rolling on the herpolhode. By transforming in the complex
momentum plane and continuing to roll right round the pole, we can see
that the apparent velocity actually lies on a non-positive
infinitesimal casual generator, which is equivalent to measurements of
a second series of tape measures moving _backwards_ in time. In fact,
it may be considered that there is only a single tape measure with many
branches, so the causality really works out OK, although at first
glance it may seem paradoxical.
This simple point trips up many tyros, and causes a lot of unnecessary
argument, though it's hard to imagine how anybody could be confused
once you see the trick!
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| User: "Ken Muldrew" |
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| Title: Re: Why does measuring tape bend one way? |
14 Feb 2005 01:10:47 PM |
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"Edward Green" <spamspamspam3@netzero.com> wrote:
This simple point trips up many tyros, and causes a lot of unnecessary
argument, though it's hard to imagine how anybody could be confused
once you see the trick!
Indeed! I hope you submitted the patent before giving away the secret.
;-)
Ken Muldrew
kmuldrezw@ucalgazry.ca
(remove all letters after y in the alphabet)
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| User: "Uncle Al" |
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| Title: Re: Why does measuring tape bend one way? |
04 Feb 2005 11:50:18 AM |
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wrote:
Why does metal measuring tape easily bend one way but not the other?
Curvature.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
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| User: "" |
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| Title: Re: Why does measuring tape bend one way? |
04 Feb 2005 12:10:37 PM |
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Curvature.
Al I have met many like you who "think" they know the answer, but
you don't have a clue.
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| User: "Androcles Androcles@ MyPlace.org" |
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| Title: Re: Why does measuring tape bend one way? |
04 Feb 2005 02:52:38 PM |
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<lemo5@optonline.net> wrote in message
news:1107540637.062548.120250@g14g2000cwa.googlegroups.com...
Curvature.
Al I have met many like you who "think" they know the answer, but
you don't have a clue.
You've noticed how simple-minded the cretin is, huh?
He even thinks winter is at apogee, and his knowledge of relativity
extends to quoting some kiddy web pages.
Androcles.
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| User: "tj Frazir" |
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| Title: Re: Why does measuring tape bend one way? BUSTED |
04 Feb 2005 04:38:57 PM |
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Memory .
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| User: "Uncle Al" |
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| Title: Re: Why does measuring tape bend one way? |
04 Feb 2005 03:19:45 PM |
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wrote:
Curvature.
Al I have met many like you who "think" they know the answer, but
you don't have a clue.
Curvature the answer, twit. The geometry differentially responds to
failure in compression (buckling) vs. tension. Bend it in each
direction and look, twerp. Your eyes, you idiot, use your eyes.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
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| User: "G=EMC^2 Glazier" |
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| Title: Re: Why does measuring tape bend one way? |
07 Feb 2005 07:09:02 PM |
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Being an old "tin Man" I use a 50 foot cloth tap,and it only bends down.
Gravity sees to it that it only bends down, Why would a tap want to bend
up. Metal tapes are made to stay parrel to the Earth,but gravity wins
in the end.
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| User: "" |
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| Title: Re: Why does measuring tape bend one way? |
04 Feb 2005 04:50:17 PM |
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For those who do not understand the question,
Bending it backwards creates compression on the center and tension on
the sides, and bending it forwards creates tension on the center and
compression on the sides, so why is the center more susceptible to
tension, and why are the sides more susceptible to compression?
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| User: "" |
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| Title: Re: Why does measuring tape bend one way? |
04 Feb 2005 05:01:07 PM |
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For those who do not understand the question,
Bending it backwards creates compression on the center and tension on
the sides, and bending it forwards creates tension on the center and
compression on the sides, so why is the center more susceptible to
tension, and why are the sides more susceptible to compression?
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| User: "Greysky" |
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| Title: Re: Why does measuring tape bend one way? |
06 Feb 2005 08:18:13 PM |
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<lemo5@optonline.net> wrote in message
news:1107556196.242127.97910@g14g2000cwa.googlegroups.com...
For those who do not understand the question,
Bending it backwards creates compression on the center and tension on
the sides, and bending it forwards creates tension on the center and
compression on the sides, so why is the center more susceptible to
tension, and why are the sides more susceptible to compression?
Look at the force vectors generated in the curved topology of the surface
you are deforming. The answer is staring you right in the face.
Greysky
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| User: "tj Frazir" |
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| Title: Re: Why does measuring PIPE bend one way? busted some more |
07 Feb 2005 04:56:28 PM |
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compresion memory. torsion.
why does a pipe bend is the question.
Bending back is just menory spring steel.
Compresion is what bent the tape..pipe.paper.string. wood, foil, nail,
Had the torsion side went there would be a rip,tear leak, crack ,
fracture ....
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| User: "" |
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| Title: Re: Why does measuring tape bend one way? |
06 Feb 2005 09:23:56 PM |
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Look at the force vectors generated in the curved topology of the
surface
you are deforming. The answer is staring you right in the face.
Greysky
Another burst of hot air.
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| User: "Uncle Al" |
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| Title: Re: Why does measuring tape bend one way? |
07 Feb 2005 11:10:03 AM |
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wrote:
Look at the force vectors generated in the curved topology of the
surface
you are deforming. The answer is staring you right in the face.
Greysky
Another burst of hot air.
Hey stooopid, curvature plus failure in compression vs. tension are
the corect answers. Those who know nothing should reply in kind.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
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| User: "Edward Green" |
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| Title: Re: Why does measuring tape bend one way? |
10 Feb 2005 07:05:16 PM |
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Uncle Al wrote:
lemo5@optonline.net wrote:
Look at the force vectors generated in the curved topology of the
surface
you are deforming. The answer is staring you right in the face.
Greysky
Another burst of hot air.
Hey stooopid, curvature plus failure in compression vs. tension are
the corect answers. Those who know nothing should reply in kind.
I don't really think this is an adequate answer.
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| User: "Philip Holman" |
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| Title: Re: Why does measuring tape bend one way? |
04 Feb 2005 07:10:35 PM |
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<lemo5@optonline.net> wrote in message
news:1107556196.242127.97910@g14g2000cwa.googlegroups.com...
For those who do not understand the question,
Bending it backwards creates compression on the center and tension on
the sides, and bending it forwards creates tension on the center and
compression on the sides, so why is the center more susceptible to
tension, and why are the sides more susceptible to compression?
Its all about the unsupported free edges. These are far less stable in
compression than in tension.
Phil Holman
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| User: "Edward Green" |
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| Title: Re: Why does measuring tape bend one way? |
05 Feb 2005 11:59:40 PM |
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Philip Holman wrote:
<lemo5@optonline.net> wrote in message
news:1107556196.242127.97910@g14g2000cwa.googlegroups.com...
For those who do not understand the question,
Bending it backwards creates compression on the center and tension
on
the sides, and bending it forwards creates tension on the center
and
compression on the sides, so why is the center more susceptible to
tension, and why are the sides more susceptible to compression?
Its all about the unsupported free edges. These are far less stable
in
compression than in tension.
I don't know if that's the right answer, but it's the only one which
even sounds like it might be an explanation about about the right level
of detail. Those who just said "cylindrical curvacture", for example,
neglected to explain why this section of a cylinder would bend more
easily in one direction than the other -- the whole cylinder doesn't
have that problem.
You can see this behavior merely by giving a bend to a sheet of paper
along the long axis and attempting to bend it either way along the
short axis -- one of those things which seems "intuitive" merely from
experience, but now that I look at it, I can't really explain or
understand it.
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| User: "Sam Wormley" |
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| Title: Re: Why does measuring tape bend one way? |
04 Feb 2005 02:19:45 PM |
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wrote:
Why does metal measuring tape easily bend one way but not the other?
cylindrical curvature
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| User: "robert j. kolker" |
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| Title: Re: Why does measuring tape bend one way? |
04 Feb 2005 02:29:56 PM |
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Sam Wormley wrote:
lemo5@optonline.net wrote:
Why does metal measuring tape easily bend one way but not the other?
cylindrical curvature
That is why bicycles are made of lightweight hollow cylindrical
sections. They are very hard to bend.
Bob Kolker
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| User: "ošin" |
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| Title: Re: Why does measuring tape bend one way? |
04 Feb 2005 02:13:31 PM |
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Why does metal measuring tape easily bend one way but not the other?
It is because the material of the tape flexes but does not compress.
Hmmmm. Why does your knee bend in one direction easier than the other? Why
does a barbed arrow head go into your eye easier than it comes out? And why
is it so much easier to stir milk into your coffee than out of your coffee?
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