Resist & Work With Forces & Stresses (AQA GCSE Design & Technology): Revision Note
Exam code: 8552
Tension
Tension is a force which is transmitted through a material which is being pulled
The characteristic of tension can be seen in products like steel chains or the cables of a bridge
This is where the ends are constantly being pulled away from each other
Worked Example
Explain where the force of tension would appear in a chair
Answer
Tension is a force that appears where two ends of a material are being pulled away from one another. This would appear in a chair seat, where the weight in the centre would pull the sides of the seat inwards.
Compression
Compression is a force which is transmitted through a material where the ends or sides are being pushed together
The characteristic of compression can be seen in objects like columns or pillars in buildings
The ends are constantly being pushed toward each other
Worked Example
Explain where the force of compression would appear in a chair
Answer
Compression is a force that appears where a material is being squashed together from two sides. This would appear in the chair legs, where the weight of the sitter above would push down onto the legs, and the floor would resist/push back against this, putting the legs under compression.
Bending
Bending is a force which causes a material to curve or change shape due to forces acting upon it
The characteristic of bending can be seen in objects like beams or shelves under a heavy load
For a horizontal beam, the upper part is under compression, whilst the lower part is under tension, as the object curves
Worked Example
Explain where the force of bending would appear in a chair
Answer
Bending is a force that appears where force causes a material to curve. This would appear in a chair's backrest, where the sitter would lean back against the backrest, causing it to experience bending.
Torsion
Torsion is a force which causes a material to twist when effort is applied in opposite directions to the ends of a length
The characteristic of torsion can be seen in objects like drive shafts or screwdrivers, where the force at one end is rotating in a different direction from another force acting on it
Worked Example
Explain where the force of torsion would appear in a chair
Answer
Torsion is a force that appears where two ends of a material are turning in opposite directions. This would appear when the sitter turns in the chair, against the friction of the floor below the chair. This could also be seen in a swivel chair, which is designed to spin.
Shear
Shear is a force which causes parts of a material to slide past each other
The characteristic of shear can be seen in objects like scissors or bolts, where forces act parallel but in opposite directions across the material, which in scissors makes them cut, but in a bolt would make it fail
Worked Example
Explain where the force of shear would appear in a chair.
Answer
Shear is a force that appears where material is looking to slide against another. This would appear in the bolts or screws holding the chair together, where both an upward and downward force would be acting on these parts, creating the force of shear.
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