How do structures carry loads, and what forces and methods keep them stable and strong?
Structures and forces: tension, compression, bending, shear and torsion, how structures resist them, the moment of a force and equilibrium, beams, ties and struts, triangulation, and methods of reinforcing and stiffening a structure.
A focused answer to Eduqas A-Level Product Design on structures and forces: tension, compression, bending, shear and torsion, ties and struts, the moment of a force and equilibrium, triangulation, and how structures are reinforced and stiffened, with a worked moments calculation.
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What this dot point is asking
Eduqas wants you to know the forces that act on structures (tension, compression, bending, shear, torsion), how structures resist them, the moment of a force and equilibrium, and how designers reinforce and stiffen a structure efficiently. This topic combines technical knowledge with the applied maths of moments, so it is examined as definitions, a moments calculation, and reasoning about making structures strong and light.
Forces on structures
Moments and equilibrium
Making structures strong and stiff efficiently
How structures fail and are reinforced
Structures fail when a force exceeds what a member or joint can resist: a strut may buckle (bend and collapse under compression), a tie may stretch or snap, a beam may bend or shear, and joints may pull apart. Designers prevent this with a safety factor (designing to carry more than the expected load), by reinforcing highly stressed areas, and by directing forces along members that are good at resisting them (ties in tension, struts in compression). Reinforcing concrete with steel is a classic example: concrete is strong in compression but weak in tension, so steel bars carry the tension. The exam reward is to link the force acting to the method of resisting it, and to prefer efficient geometry over brute material.
Exam-style practice questions
Practice questions written in the style of WJEC Eduqas exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Eduqas 20204 marksA uniform shelf bracket is held by a screw at the wall. A 60 N load hangs 0.20 m from the screw. Calculate the moment of the load about the screw, and state its unit.Show worked answer →
A Component 1 moments calculation. Marks for the formula, the substitution and the answer with units.
The moment of a force is the force multiplied by the perpendicular distance from the pivot: newton metres (N m). The unit is the newton metre. This turning effect must be resisted by the fixing and the bracket, which is why a heavier or further-out load needs a stronger fixing.
Award marks for the formula, the correct substitution and the unit (N m). A common dropped mark is omitting the unit or using a distance not measured perpendicular to the force.
Eduqas 20216 marksDiscuss how the forces of tension and compression act in a simple loaded beam or frame, and explain two ways a designer can make a structure stronger or stiffer without simply using more material. Use examples.Show worked answer →
A Component 1 extended question marked by levels of response. Reward the forces, and two efficient strengthening methods.
In a loaded beam, the top surface is squashed (compression) and the bottom surface is stretched (tension); members that are pulled are ties (in tension) and members that are pushed are struts (in compression). Two efficient methods: triangulation, adding diagonal members so a frame forms rigid triangles that cannot be distorted (used in bridges, roof trusses, shelving); and changing the cross-section or form, such as using an I-beam, a tube or a folded or ribbed section, which puts material where the bending stress is highest, giving more stiffness for the same mass.
A top answer explains tension and compression in the beam, gives two distinct methods (triangulation and efficient cross-section) with examples, and concludes that clever geometry beats simply adding material, which also saves weight and cost.
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