TECHNOLOGY: Structures
GRADE
TEACHERS
8
TERM
2
Topic
WHAT I am
going to
teach?
CAPS:
1. Tension;
compression;
bending;
torsion; shear.
2. Reinforcing
3. Beam
orientation to
withstand
forces
DATE:
Methodology
HOW I am going to
TEACH?
Read and discuss the
content on page 130 to
140.
Explain new vocabulary.
Allow learners to do
practical activities to
explore beams better.
WEEK:
5
Resources
WHAT I am going to use?
MST Technology
Teacher’s guide page
130 to 140 or
http://www.mstworkbook
s.co.za/technology/gr8/t
ableofcontents.html
Physical examples of
different beams
Time: 2 Hours
Same as
above.
PARENTS
Same as above.
Tips to parents.
Let your child read the
content page aloud and
make notes of concepts.
MST Technology
workbook (Learner’s
guide page 130 to 140)
(http://www.mstworkboo
ks.co.za/technology/gr8/
tableofcontents.html)
Stop, ask questions and
explain new words.
New words could be
written down on a piece
of paper and then stuck
up on the wall to recap
later.
LEARNERS’
ACTIVITIES
Learners engage with the content and participate in the discussion.
Learners identify different forces and experiment with examples.
Learners complete the worksheet
Informal
Assessment
Complete the questions in the worksheet.
STRUCTURES CONTINUED
1|Page
Content
Tension
Compression
Bending
Torsion
Shear force
Explanation
Two pulling forces, directly opposing each
other, that stretch an object and try to pull it
apart. For example, pulling on a rope.
Two pushing forces, directly opposing each other, that
push against an object and try to compress it. For
example, pushing on an empty can.
When the forces are aligned towards each other, they
are called compression forces
If an uneven force is applied to an object, it will tend
to change shape and bend. For example bending a
metal wire.
Torsion is the twisting of an object due to an applied torque
(turning force)
Shearing forces are unaligned forces pushing one part of a body
in one specific direction, and another part of the body in the
opposite direction.
pillar
A tall vertical structure of concrete, wood, or metal,
used as a support for a building or heavy bridge
Beam
A beam is a structural element that primarily resists bending
loads applied to it
Reinforcing
To make a structure withstand large tensile and compressive
forces, another type of strong material is put inside the structure
Reinforced
concrete
To make concrete withstand large tensile and compression forces,
steel rods or mesh is placed in the concrete when the wet concrete
is poured into a shape or mold. Page 131 and 132
Plywood
Plywood is a made by glueing many thin layers of wood
on top of one another. The grain in each layer is at a
right angle to the grains in the layers above and below
it. Plywood can therefore withstand large tensile forces in
both directions. Page 133
2|Page
Elastic
When you stop pushing or pulling an elastic
material, it returns to its original shape
Fracture
If a material is bent too far it will crack (fracture).
I-beam
Beams can be shaped in
special ways to make them
resist bending. The shape
called an I-beam is a shape
that resists bending very well.
Complete the worksheet in your classwork book: (pages 137 to 140 Learner’s workbook)
You will have to read the pages and understand the explanations before you will be
able to answer the questions.
Investigate: What forces act inside a beam that bends?
The pictures shows an imagined idea that wood is made
of a lot of little blocks that are connected by springs.
1. What happens to the imaginary springs when a
tensile (pulling) force acts along the
length of the beam?
2. What happens to the imaginary springs when a
compressive (pushing) force acts along
the length of the beam?
3. In the picture below, what type of force acts along the top of the beam when it bends
down?
4. What type of force acts along the bottom of the beam when it bends down?
5. Is there a tensile or compressive force acting along the middle of the beam
when it bends down?
6. Look at the thick beam (top right). There are seven rows or layers of blocks
connected with springs. The layers are numbered.
(a) Which two layers of the beam help it the most to resist bending?
(b) Does the middle layer of a beam help it to resist bending?
3|Page
7. Which beam will bend the least if
the same load is applied to both
beams?
8. What will happen to beam C when
there is a sideways force?
Consolidation
Engineers wanted to design a new shape for a beam that will resist bending more
than beam A, but without buckling like beam C. They knew that the material in the
middle of a beam does help a lot to resist bending, because it does not stretch or
compress a lot in the middle of a beam when it bends. So they took the design of beam
A, and removed some material from the middle and rather added it to the top and
bottom, where there will be more stretching and
compression. In this way, they made the beam taller, but they also added short
horizontal parts at the top and the bottom to prevent the beam from buckling
sideways. This is shown in the pictures
Because an I-beam resists bending better, a lighter and cheaper I-beam can
be used to carry the same load as a rectangular beam. That also means that less
steel will have to be made, so less energy will be used to make steel. In this way,
clever design of material helps to reduce the negative impact of technology on the
environment.
Rectangular beam
I-Beam
4|Page