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Strength of Shapes

A A forceforce is a push or pull exerted by one is a push or pull exerted by one object on another.object on another.

A tensile force expands or lengthens the object it is acting on.

A compressive force compresses or shortens the object it is acting on.

Forces in Tension and Compression

The rope is in tension

The stand is in compression.

Forces in Tension and Compression

Which shapes are strongest?

Which deform when in tension?

Which deform in compression?

It depends on where you hold it and where you push or pull (top, bottom, sides…). Insert pipe cleaners into plastic straws and twist the ends to test different shapes. What happens?

Forces on Shapes

Triangles are the only shapes that cannot be deformed without changing the length of one of its sides

Arches are strong because the force resulting from a heavy load placed at the top spreads down the sides to the foundation.

A group of arches placed around a central point creates a dome, which distributes loads down through curving sides to the foundation.

Engineers consider shapes Engineers consider shapes under heavy loads when under heavy loads when building large structures.building large structures.

Forces on Shapes

Stansted AirportCentre Pompidou

Eiffel Tower Bank of China Tower

Roman Colosseum

Iron Bridge at Coalbrookdale

Musee d'OrsaySan Lorenzo, Florence

Florence CathedralSuleyman Mosque

US Pavilion at Expo '67 - spherical structure made of trianglesDome tent -poles bent into arches

with nylon fabric in tension.

Psyclone Rollercoaster- triangles in structure

Campo Volantin Footbridge - arch with cables in tension