Forces And Stresses
Muhtasari
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.
Malengo
- Tension, compression, bending, torsion and shear.
- Stress and strain
- How materials can be reinforced, stiffened or made more flexible: eg lamination, bending, folding.
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Maelezo ya Somo
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Tathmini ya Somo
Hongera kwa kukamilisha somo la Forces And Stresses. Sasa kwa kuwa umechunguza dhana na mawazo muhimu, ni wakati wa kuweka ujuzi wako kwa mtihani. Sehemu hii inatoa mazoezi mbalimbali maswali yaliyoundwa ili kuimarisha uelewaji wako na kukusaidia kupima ufahamu wako wa nyenzo.
Utakutana na mchanganyiko wa aina mbalimbali za maswali, ikiwemo maswali ya kuchagua jibu sahihi, maswali ya majibu mafupi, na maswali ya insha. Kila swali limebuniwa kwa umakini ili kupima vipengele tofauti vya maarifa yako na ujuzi wa kufikiri kwa makini.
Tumia sehemu hii ya tathmini kama fursa ya kuimarisha uelewa wako wa mada na kubaini maeneo yoyote ambapo unaweza kuhitaji kusoma zaidi. Usikatishwe tamaa na changamoto zozote utakazokutana nazo; badala yake, zitazame kama fursa za kukua na kuboresha.
- 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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