![[Purpose:]](../../inline/purpose.gif)
- To investigate the strength of structures by constructing a Dynamic
Dome.
![[Theory:]](../../inline/theory.gif)
This project is versatile, cost effective, and fun to do. Dynamic
Domes demonstrate everything from structures to space. The domes are
approximately 4 metres (13') in diameter by 2 metres (7') tall. They have a
carrying capacity of approximately 113 kilograms (250 pounds) when loaded
through the centre point.
Which shapes are strongest? Did you know that a triangle is stronger
than a square? The triangle is the only shape that cannot be deformed
without changing the length of one of its sides. The arch, a variation of
the triangle, distributes forces more evenly. If you think about it, a dome
is simply made up of many arches. Can you think of any bridges or buildings
that use triangles or arches to make them stronger? In the dome you are
about to build, the arches will be made from 24 pipes. Naturally, the more
pipes you have, the stronger the dome will be.
![[Materials:]](../../inline/material.gif)
-
Tools
- Table saw
- Drill press
- Band saw
- Pencil
- Tape measure
- Protractor
- Circle scribe
- 1" wood bit
- 5/16" wood bit
Components
- 24 10' lengths of 3/4" PVC
- 12 4' long 2 x 4's
- 3 16" x 16" x 3/4" plywood
- 50 5" long 1/4" threaded bolts
- 1 5" long 1/4" eye bolt
- 50 wing nuts
- 100 washers
![[Procedure:]](../../inline/procedure.gif)
- Constructing the Dome
- Using the protractor, measure two 75 degree angles, 36" apart, on
the 2 x 4's as shown in figure 1.
![[The lines along which the 2 x 4 should be cut]](inline/domes1.gif)
- Cut the boards along the lines by using the table saw.
- Next, cut the remaining one-foot lengths of 2 x 4's into 8" lengths cut
at 90 degrees.
- From one of the 3/4" plywood boards, cut 12 pieces of wood that are 8"
long by 3.5" wide to match up with the 2 x 4's that were cut earlier.
- Cut the 24 pipes to 10' lengths.
- Number each of the twelve 8" 2 x 4 and 3/4" blocks along with the angle
cut 2 x 4's from 1 to 12.
- Take the two corresponding numbered blocks and mark off two locations on
the 3/4" board that are 1/5" from each of the long ends and along the
centre.
- Place the 3/4" board on top of the 2 x 4 and drill through both at the
same time.
- Countersink a hole 1/4" deep into the 2 x 4 blocks with the 1" wood bit
(later this will hide the bolt heads so they do not scratch the floor in
case the dome is to be used inside).
- Print a number 1 on the second board on the end that is nearest the
first printed number 1.
- Butt a second 36" 2 x 4 against the first number 1 so they begin to form
a circle.
- Print a number 1 on the second board on the end that is nearest the
first printed number 1.
- Place the 3/4" board over the seam so it is centred, and use the pencil
to mark two locations - one on each of the two 36" 2 x 4's that you just
marked.
- Repeat this procedure for all 12 sets of blocks until the base circle is
complete.
- Next, measure 10.5" along centre from each of the ends of the twelve
36" 2 x 4's.
- At each of these locations, drill a 1" diameter hole - the pipes will be
put through these holes later. Note that if the dome is being used for a
star lab, you may want to space these holes apart on one of the boards to
create a door when the dome in finished. This concludes the construction of
the base.
- Use the circle scribe to make a 16" diameter circle on the two remaining
3/4" boards. Be sure to mark where the centre of the circle is so you can
drill a hole later.
- Cut these boards on the band saw. You can cut them both at the same
time, if it's easier.
- Use the protractor to create lines on the circles every 15 degrees
through the centre of the circle.
- Along each of these lines from centre, measure 6" out, which should be
2" from the edge.
- Place this marked circle on top of the second circle and clamp together
if possible.
- On the edge, draw a line across each board in two places. Mark that A
and B on each board. This is to ensure all the holes line up correctly
during assembly.
- At each of these 24 marks, drill a hole with the 5/16" drill bit.
- Drill a hole with the 5/16" drill bit 1.5" from the end - on only one
end of the pipe.
Note: Here's how to make screwdrivers from scrap ends of 2 x 4's.
- Drill a 5/16" hole 3" in the middle of the cut end.
- Cut a slot on the edge, wide enough for the head of a wing nut. These
can be used to tighten bolts without hurting your fingers.
Assembling the Dome You can use the Dynamic Domes to investigate
many different topics. The following procedure can be used for studying
structures and pulleys. Note: Be
sure to have a large area in which to perform this activity. Outdoors is
preferable, but the dome can be built indoors if there is sufficient
space.
- Arrange the 12 angled boards in a circle.
- Place the corresponding numbered blocks by each pair of numbers from 1
to 12 on the angled boards.
- Place 4 washers, 2 bolts, and 2 wing
nuts at each of the 12 numbered locations.
- Put a washer on each of
the bolts, push them through the 2 x 4 blocks from the countersunk side, and
place this on the ground with the bolts in the air (see figure 2).
- Place the two angled boards with corresponding numbers over the two
bolts.
Place the 3/4" board over the bolts to hold in place from
the top. - Place a washer over each of the bolts and tighten with a
wing nut. All wing nuts can be tightened with the screw drivers made
according to instructions in the construction section.
- Once the
base is complete, put washers on 24 bolts and place them through one of the
circles.
- Tip the circle with bolts over and place it on top of two
of the wooden screwdrivers.
- Place one pipe over each of the 24
large holes with the hole going over a corresponding bolt in the
centre.
- When all holes have been placed on the bolts, place the top
circle on so the A and B are aligned. Push the bolts up through the second
circle (see figure 3).
- Place washers and wing nuts on all the
bolts.
- You'll need a person at the end of each pole. Have two
people lift the centre while each person places his pole down into the
corresponding holes.
The dome is now in place, and you can try
hanging from it if you wish. - Place the eye bolt through the centre
hole and hang the pulleys.
- First one pulley is used, and you can
try lifting a weight and then pulling it with the single pulley. It does
not get lighter to lift, but you can now pull in a different direction.
- Set up a compound pulley using 4 pulleys.
- Try to lift the
weight again. Why has the compound pulley made it a lot easier to lift?
You cannot push on a rope (you can only pull on it), so the force in the
rope is constant throughout. The compound pulley made use of four ropes to
lift the weight instead of a single rope. As a result, it was four times
easier to lift the weight, but you had to pull four times as much rope.
- Dismantle the dome in the reverse order to which it was assembled.
![[Conclusions:]](../../inline/concl.gif)
This experiment proves just how strong the dome shape is. You and your
friends can hang from it, sit on top of it, and even test pulleys with it!
This demonstrates compression and tension.
Compression is a pushing force - it squashes materials. Look for
materials in compression in tree trunks, pyramids, and arch bridges.
Tension is a pulling force - it stretches materials. Look for materials
in tension in telephone wires, suspension bridges, steel elevator cables,
and inflated stadium domes.
Have you ever broken an egg by squeezing it between your fingers?
Perhaps, if you squeezed in the middle, but try squeezing the ends evenly
between your hands. You can think of an egg as two domes glued together - a
sturdy structure indeed!