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Grade 7

Structures and communication

Module 22

Reinforcing doors and windows

REINFORCING, by using concrete and lintels over doors and window openings.


Structures are stabilized to prevent them from collapsing when forces or loads are put on them. To prevent a structure from falling down or collapsing we must try to make the internal forces bigger than the external forces under all conditions. How can you prevent a chair from collapsing when you sit on it? There are rails acting as ties at the bottom holding the legs together and preventing the legs from being pushed outwards.

A flagpole doesn’t need any supports under normal conditions. When the wind blows it can be supported by using guy ropes or ties that are flexible, but stop the poles from bending too far.

Different forces can act on different parts of a structure. Forces that structures have to stand up to are:

  • Compression – when we try to squash a structure ( a squashing force).
  • Tension – when we try to pull a structure apart from either end (a pulling force).

  • Bending – a force which is trying to bend a structure and it is in compression and tension simultaneously.
  • Torsion – a turning or twisting force like when you twist the top off a bottle.
  • Shear – a force created when two opposite forces try to cut a material; like when you use a pair of scissors to cut a piece of paper.

When one force is balanced by another they are said to be in EQUILIBRIUM.

When you build a structure, you do not always have to use solid material like wood or metal. Flexible material, such as wire, can be used for parts of the structure which will only be stretched or in tension. Wire can be used in tension (being stretched), but not in compression (be squashed).

Load from the top of the structure keeps the wire in tension and the structure remains rigid.

When the structure is loaded from the sides the wire is compressed (squashed) and it collapses. It is unstable.

Triangles are very useful when building structures. They can help to make a very strong and rigid structure. To make a rectangle more stable is to put in two more members from corner to corner. Four triangles are formed. This way of making structures more stable is called TRIANGULATION. It is often used when building bridges or cranes. It is not always necessary to put in two members, one would be enough. The second extra member is called the redundant member. When designing structures it is easy to use more members that are really needed. They will only add more weight to the finished structure and make it more expensive.

By making the base size of a structure heavier or wider, you can also make it more stable.

Assignment 1 (groupwork):

[lo 2.1]

Choice 1:

Design and make a horizontal structure using 25 paper straws and a glue gun. Your structure must support a marble as far out from the table as possible. Your structure must not come in contact with the floor or any of the other furniture in the room. It must support the marble for at least 30 seconds.

Choice 2:

Design and make a tower using 25 paper straws and a glue gun. Your tower must support a marble for at least 30 seconds as high as possible.

It is also important to get a structure’s centre of gravity so that it is able to balance. All objects have a point where they are held in balance by the force of gravity. This balancing point is called the centre of gravity, because it is the place where the whole weight of the object seems to centre. The balancing point of a rectangular shape, such as a square or a circle, is in the centre.

How can you find the balancing point of an irregular shape?

Where do you think is the best place for the heavy cargo to be stowed on a ship?

Gravity is the pull that objects have on other objects around them. Because the Earth itself is the largest object in our world, the pull of its gravity is the strongest we can feel. Gravity keeps everything resting on the ground. An object centre of gravity is found when it just balances on the edge of a table before it falls off.

Any object will balance on a pivot when its centre of gravity is low.

How can you change an object’s centre of gravity?

Assignment 2:

To make your own trapeze artist

[lo 2.1]

Requirements :

  • Thick white card
  • a drawing pin
  • a scissors
  • felt tip pens
  • strong glue
  • wire
  • 2 plasticine balls
  • a heavy bottle
  • a glue gun
  • pliers


  1. Draw the man shape onto some thick white card. Carefully cut out the shape with scissors.

1. Colour in the man to make him more human in the front and back using felt tip pens. Carefully glue a drawing pin to the bottom of the card.

  1. Cut of a length of wire using pliers. Glue it into place with the glue gun.

  1. Glue two plasticine balls to each end of the wire.

4. Carefully stand the balancing man on top of a bottle. He wobbles slightly, but should keep his balance.


Paper/card Glue, paper clips, a stapler, paper fasteners, washers, string or yarn, tape, pins
Textile Textile glue glues material onto material, PVA glue glues material to paper, card or wood, string , yarn, fasteners (buttons, velcro, zips, hooks and eyes, snap-fasteners, press-studs, strings, laces, ribbon)
Wood Nails, pins, screws, woodglue, joints
Metal Screws, bolts and nuts, soldering, glue, rivets
Plastic Screws, glue


Assessment standards (ASs)
We know this when the learner:
2.1 demonstrates knowledge and understanding of structures.
processing :2.2 demonstrates knowledge and understanding of how materials can be processed to change or improve properties (e.g. strength, fire resistance, waterproofing, taste, volume, texture).

Questions & Answers

can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
okay, so you have 6 raised to the power of 2. what is that part of your answer
I don't understand what the A with approx sign and the boxed x mean
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
I'm not sure why it wrote it the other way
I got X =-6
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
oops. ignore that.
so you not have an equal sign anywhere in the original equation?
Commplementary angles
Idrissa Reply
im all ears I need to learn
right! what he said ⤴⤴⤴
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
im not good at math so would this help me
Rachael Reply
I'm not good at math so would you help me
what is the problem that i will help you to self with?
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Technology grade 7. OpenStax CNX. Sep 10, 2009 Download for free at http://cnx.org/content/col11032/1.1
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