Background knowledge
In large structures, when parts break, the effects can be dramatic. Here are some examples. On 2 April 2011, a Boeing 737 was forced to make an emergency landing at an airport in the United States of America. The reason was due to the fact that the roof of the plane was ripped open while the plane was in flight. The cause of this was probably a structural member breaking due to the torsion forces on the plane’s structure. In this case the plane was able to land and no lives were lost. In 1998 the Injaka Bridge in Mpumalanga collapsed during construction, killing 14
workers and injuring 19 others. The cause of the collapse was the failure of the temporary structural members used during construction. The textbook refers to two other dramatic failures: the Tay River Bridge disaster in
Scotland and the collapse of the World Trade Centre Twin Towers. All these disasters have different causes. It is impossible for designers and engineers to
foresee all that might happen to a structure but they do need to consider the choice of materials and the type of construction in order to design structures which can withstand the normal forces applied to them.
Activity 1 Test the strength of materials Learner’s Book page 30 Guidelines to implement this activity
• This is a group activity. • Divide the learners into groups of 3–4. • In this activity the learners are going to test the strength of different materials by dropping a heavy steel ball such as a shotput used in athletics onto them.
• If you cannot get a shotput, then use a heavy sledgehammer head. • Place the sample in a box to prevent accidents from small pieces that break off. • Another safety measure is to make sure that the learners stand clear until after the ball has been dropped.
• It is important that learners begin to learn that they need to record the results of tests. • They should write a report in which they describe what materials they tested, how they tested them and what the results of the test were.
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