# Topic – Forces and Shapes

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### Forces and Shapes

Strong shapes are used when people design buildings. These shapes make buildings that can withstand the forces that act on them. Three strong shapes are often used in buildings. These shapes are rectangles, arches, and triangles.

In the diagrams below, the pairs of arrows show the following forces at work:

### Rectangles

A rectangle can be quite strong. But it is not as strong when a force pushes on one of the vertical sides. Its shape can change, making it weaker. Builders add a diagonal support piece to make the rectangle stronger. This support piece is called a brace. It goes between two opposite corners of the rectangle.

### Arches

An arch is a strong shape. But it is not as strong when a force pushes down on the top of the arch. When a force pushes down on the top of the arch, the sides of the arch spread outward. To make an arch stronger, builders add supports on each side. These supports are called buttresses. The buttresses prevent the sides of the arch from spreading outward.

### Triangles

A triangle can be a very strong shape. If a force pushes on the top point, the triangle is very strong. But if a force pushes on the side of a triangle, the side can bend.

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