Forces And Stresses
Overview
Take a sheet of paper by one edge and hold it out flat. It flops. Now fold a lip of ten millimetres along the front edge and hold it out again, and it stands almost straight. You have added nothing. The paper is the same mass, the same material and the same thickness, and it is many times stiffer, because you changed the shape of its section rather than the amount of material in it.
That trick, and the arithmetic behind it, is the most useful thing in this lesson. You will learn the five forces the specification names, tension, compression, bending, torsion and shear, and how to spot which one is acting where in a product. You will calculate stress from force and cross sectional area, and strain from the change in length and the original length, which are the two formulae the specification's own maths column prints beside this section. And you will learn how materials can be reinforced, stiffened or made more flexible, using lamination, bending and folding, so that a design survives a load it would otherwise fail under. This is specialist technical principles content, examined in Section B of Paper 1.
Objectives
- Tension, compression, bending, torsion and shear.
- Stress and strain
- How materials can be reinforced, stiffened or made more flexible: eg lamination, bending, folding.
Mind map
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Lesson Note
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Lesson Evaluation
Congratulations on completing the lesson on Forces And Stresses. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- A force that twists a material about its own axis is called A. bending. B. compression. C. shear. D. torsion. Answer: D
- A rod of cross sectional area 50 square millimetres carries a tensile force of 2,000 newtons. What is the stress? A. 4 newtons per square millimetre B. 40 newtons per square millimetre C. 400 newtons per square millimetre D. 100,000 newtons per square millimetre Answer: B
- Which one of the following stiffens a sheet without adding any material? A. Bonding a second sheet to it B. Folding a lip along its edge C. Using a thicker gauge of sheet D. Riveting a plate across it Answer: B
- When a beam bends downwards, the material at the top surface is in A. compression. B. shear. C. tension. D. torsion. Answer: A
- A 500 millimetre cable stretches by 2 millimetres under load. What is the strain? A. 0.004 B. 0.04 C. 0.4 D. 250 Answer: A
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