| Topic: |
Science > Physics |
| User: |
"shutout31" |
| Date: |
17 Feb 2004 05:40:36 PM |
| Object: |
Cantilever project - easy question |
Hi, I'm doing a project for my HS physics class. I need to build a
cantilever out of craft sticks (I'm using thin bass wood sticks) that
needs to be at least 12 inches long. I'm being graded on the
efficiency of it by weight (amount of weight it holds on the end
divided by the weight of the cantilever). One end will be fixed while
the other end will have the weight at 12 inches out. The teacher will
add weight until it breaks. I have two plans that I narrowed it down
to but I need your opinion for which design would be more efficient,
look here for the rough sketches:
http://images.cardomain.com/member_images/3/web/507000-507999/507399_15_full.jpg
The design will be have two sides like that and single pieces of wood
to connect the two.
The other question I have is what angles should I make the triangles?
90-45-45 or 60-60-60?
Thanks in advance.
- Scott
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| User: "shutout31" |
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| Title: re:Cantilever project - easy question |
17 Feb 2004 07:43:47 PM |
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anyone please?
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| User: "Uncle Al" |
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| Title: Re: Cantilever project - easy question |
17 Feb 2004 06:25:48 PM |
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shutout31 wrote:
Hi, I'm doing a project for my HS physics class. I need to build a
cantilever out of craft sticks (I'm using thin bass wood sticks) that
needs to be at least 12 inches long. I'm being graded on the
efficiency of it by weight (amount of weight it holds on the end
divided by the weight of the cantilever). One end will be fixed while
the other end will have the weight at 12 inches out. The teacher will
add weight until it breaks. I have two plans that I narrowed it down
to but I need your opinion for which design would be more efficient,
look here for the rough sketches:
http://images.cardomain.com/member_images/3/web/507000-507999/507399_15_full.jpg
The design will be have two sides like that and single pieces of wood
to connect the two.
The other question I have is what angles should I make the triangles?
90-45-45 or 60-60-60?
Thanks in advance.
1) Look at the Eiffel Tower, bridges, and especially *airplane
wings* for structure.
2) Look at long arm cranes for cantilever support.
3) How does stiffness of a rectangular beam vary with thickness?
(Ask an orthodontist) How does mass do likewise? Do you do better
toward balsa or oak and ash? Pay attention to the grain direction,
especially tension vs. compression.
4) Use carpenter's glue. Roughen glued surfaces before gluing.
Give it time to fully set.
5) How do wood's properties change with moisture content?
6) How does wood fail in tension and in compression? That tells you
a lot about what to put top and bottom.
7) Honeycomb reinforcement. Should the faces of the triangles be
vertical or horizontal vs. the stress?
http://www.hexcelcomposites.com/About/Default.htm
It doesn't hurt to make two or three different models, certainly
sub-assemblies, and test them to destruction yourself. Engineering
theory said "Tacoma Narrows Bridge," but reality said "Galloping
Gertie."
Google
"galloping gertie" 1930 hits
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
"Quis custodiet ipsos custodes?" The Net!
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| User: "Mark Folsom" |
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| Title: Re: Cantilever project - easy question |
17 Feb 2004 11:09:37 PM |
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"Uncle Al" <UncleAl0@hate.spam.net> wrote in message
news:4032B10C.A4818E16@hate.spam.net...
shutout31 wrote:
Hi, I'm doing a project for my HS physics class. I need to build a
cantilever out of craft sticks (I'm using thin bass wood sticks) that
needs to be at least 12 inches long. I'm being graded on the
efficiency of it by weight (amount of weight it holds on the end
divided by the weight of the cantilever). One end will be fixed while
the other end will have the weight at 12 inches out. The teacher will
add weight until it breaks. I have two plans that I narrowed it down
to but I need your opinion for which design would be more efficient,
look here for the rough sketches:
http://images.cardomain.com/member_images/3/web/507000-507999/507399_15_full.jpg
The design will be have two sides like that and single pieces of wood
to connect the two.
The other question I have is what angles should I make the triangles?
90-45-45 or 60-60-60?
Thanks in advance.
1) Look at the Eiffel Tower, bridges, and especially *airplane
wings* for structure.
2) Look at long arm cranes for cantilever support.
3) How does stiffness of a rectangular beam vary with thickness?
(Ask an orthodontist) How does mass do likewise? Do you do better
toward balsa or oak and ash? Pay attention to the grain direction,
especially tension vs. compression.
4) Use carpenter's glue. Roughen glued surfaces before gluing.
Give it time to fully set.
5) How do wood's properties change with moisture content?
6) How does wood fail in tension and in compression? That tells you
a lot about what to put top and bottom.
7) Honeycomb reinforcement. Should the faces of the triangles be
vertical or horizontal vs. the stress?
http://www.hexcelcomposites.com/About/Default.htm
It doesn't hurt to make two or three different models, certainly
sub-assemblies, and test them to destruction yourself. Engineering
theory said "Tacoma Narrows Bridge," but reality said "Galloping
Gertie."
I had a C-beam project for a college engineering class. The instructor said
that the glue was always stronger than the wood. So I built a truss
structure that loaded all the balsa wood in tension or compression. It
failed at the glue joints every time--the winner was a box beam with really
long glue joints.
Mark Folsom
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| User: "Greg Neill" |
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| Title: Re: Cantilever project - easy question |
18 Feb 2004 09:26:17 AM |
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"Mark Folsom" <folsom_snip_man@redshift.com> wrote in message
news:1035u6hcvi681fd@corp.supernews.com...
I had a C-beam project for a college engineering class. The instructor
said
that the glue was always stronger than the wood. So I built a truss
structure that loaded all the balsa wood in tension or compression. It
failed at the glue joints every time--the winner was a box beam with
really
long glue joints.
Talk to woodworkers about glue joints. End grain situations
make for lousy joint strength. Cross grain is better, but
aligned grain is the best situation, in which case the glue
joint will be much stronger than the wood itself.
.
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| User: "Creative Music Synth [220]" |
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| Title: Re: Cantilever project - easy question |
18 Feb 2004 02:31:01 PM |
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I am the best MIDI output
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| User: "Richard Herring" |
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| Title: Re: Cantilever project - easy question |
18 Feb 2004 07:47:02 AM |
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In message <4032B10C.A4818E16@hate.spam.net>, Uncle Al
<UncleAl0@hate.spam.net> writes
shutout31 wrote:
Hi, I'm doing a project for my HS physics class. I need to build a
cantilever out of craft sticks (I'm using thin bass wood sticks) that
needs to be at least 12 inches long. I'm being graded on the
efficiency of it by weight (amount of weight it holds on the end
divided by the weight of the cantilever). One end will be fixed while
the other end will have the weight at 12 inches out. The teacher will
add weight until it breaks. I have two plans that I narrowed it down
to but I need your opinion for which design would be more efficient,
look here for the rough sketches:
http://images.cardomain.com/member_images/3/web/507000-507999/507399_15
_full.jpg
The design will be have two sides like that and single pieces of wood
to connect the two.
The other question I have is what angles should I make the triangles?
90-45-45 or 60-60-60?
Thanks in advance.
1) Look at the Eiffel Tower, bridges, and especially *airplane
wings* for structure.
2) Look at long arm cranes for cantilever support.
3) How does stiffness of a rectangular beam vary with thickness?
(Ask an orthodontist) How does mass do likewise? Do you do better
toward balsa or oak and ash? Pay attention to the grain direction,
especially tension vs. compression.
4) Use carpenter's glue. Roughen glued surfaces before gluing.
Give it time to fully set.
5) How do wood's properties change with moisture content?
6) How does wood fail in tension and in compression? That tells you
a lot about what to put top and bottom.
7) Honeycomb reinforcement. Should the faces of the triangles be
vertical or horizontal vs. the stress?
8) Look out for unexpected modes. It might be rigid on the drawing
board, but can the reality twist and droop out of the plane of the
drawing?
--
Richard Herring
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| User: "John Popelish" |
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| Title: Re: Cantilever project - easy question |
17 Feb 2004 08:11:40 PM |
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shutout31 wrote:
Hi, I'm doing a project for my HS physics class. I need to build a
cantilever out of craft sticks (I'm using thin bass wood sticks) that
needs to be at least 12 inches long. I'm being graded on the
efficiency of it by weight (amount of weight it holds on the end
divided by the weight of the cantilever). One end will be fixed while
the other end will have the weight at 12 inches out. The teacher will
add weight until it breaks. I have two plans that I narrowed it down
to but I need your opinion for which design would be more efficient,
look here for the rough sketches:
http://images.cardomain.com/member_images/3/web/507000-507999/507399_15_full.jpg
The design will be have two sides like that and single pieces of wood
to connect the two.
The other question I have is what angles should I make the triangles?
90-45-45 or 60-60-60?
Thanks in advance.
What is the structure attached to, and by what means?
Forget the details until you consider that tension members do not need
buckle prevention, but compression members do.
--
John Popelish
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| User: "Richard Herring" |
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| Title: Re: Cantilever project - easy question |
18 Feb 2004 07:52:50 AM |
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In message <4032C9DC.E35C4F49@rica.net>, John Popelish
<jpopelish@rica.net> writes
shutout31 wrote:
Hi, I'm doing a project for my HS physics class. I need to build a
cantilever out of craft sticks (I'm using thin bass wood sticks) that
needs to be at least 12 inches long. I'm being graded on the
efficiency of it by weight (amount of weight it holds on the end
divided by the weight of the cantilever). One end will be fixed while
the other end will have the weight at 12 inches out. The teacher will
add weight until it breaks. I have two plans that I narrowed it down
to but I need your opinion for which design would be more efficient,
look here for the rough sketches:
http://images.cardomain.com/member_images/3/web/507000-507999/507399_15
_full.jpg
The design will be have two sides like that and single pieces of wood
to connect the two.
The other question I have is what angles should I make the triangles?
90-45-45 or 60-60-60?
Thanks in advance.
What is the structure attached to, and by what means?
Forget the details until you consider that tension members do not need
buckle prevention, but compression members do.
On that note, it's interesting to recall Hooke's insight into designing
the supports for the dome of St Paul's.
--
Richard Herring
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