Forces and loads in structures — Engineering, 11–13 years
A structure stays safe when forces are carried through its parts to the ground without bending, sliding or breaking.
Forces need a path
A load is a push or pull that a structure must carry, such as people on a floor or snow on a roof. The structure passes that force through beams, joints and supports into the ground. Each part must be strong enough and connected well enough for the force to travel safely.
Why engineers trace loads
A bridge can look solid and still fail if a force has nowhere safe to go. Engineers learned to trace loads because gravity, wind and moving vehicles constantly push or pull structures. Knowing the path helps them place supports and material where they are truly needed, instead of simply making everything thicker.
A shelf holding books
A shelf holds 6 books weighing 2 newtons each, so the total load is 6 × 2 = 12 newtons downward. The shelf pushes upward on the books, while its brackets carry the force to the wall. If one bracket carries 7 newtons and the other 5, together they balance the 12-newton load.
Weight is not the only force
A common mistake is to look only at the downward weight and forget the upward support or sideways forces. That is reasonable because weight is easy to see in a calculation. But a structure is safe only when all important pushes and pulls are considered, including wind, movement and forces at joints.
Where load paths matter
Load paths matter in bridges, roofs, cranes, shelves and playground equipment. They also matter in a bicycle: your weight travels through the seat, frame, wheels and tyres to the road. Designers do not use this idea to explain every failure, but it is essential when checking how a structure carries a force.
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