Geometry versus Forces

Geometry versus Forces

Geometry versus Forces
Reading Level

	edHelper's suggested reading level:	grades 6 to 7
	Flesch-Kincaid grade level:	5.72

Vocabulary

	challenging words:		absorbers, versus, withstand, stiffen, bridges, affected, compression, gravity, divide, mass, tension, responsible, layer, absorb, design, lateral
	content words:		Tough-Shape Battle, Ancient Egypt, Great Pyramid, Eiffel Tower, These TMD

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Geometry versus Forces
By Trista L. Pollard

¹     The headlines read, "Triangle versus Square and Rectangle in the Tough-Shape Battle of the Century!" Who do you think will win? Well, if you said the triangle would win, you were right. Look around, and you will notice that most of our buildings are shaped like rectangles and squares. However, if you look closely, you will see that those same buildings may include triangles. Triangles are the strongest geometric shape in the world. Its shape is very simple: a flat base with two sides that come together at the top to meet at a point. Triangles are rigid, able to stand freely, and able to support their own weight under the forces of gravity. So when did the first builder use the triangle as a design?

²     Many years ago in Ancient Egypt, builders designed huge pyramids. A pyramid is a building that has a square base or bottom. It has four sides shaped like triangles that meet at the top in a point. One of the oldest pyramids in Egypt is called the Great Pyramid of Khufu. It was built around 2575 BC. This pyramid is one of the largest surviving pyramids in the world today. It is about 480 feet tall, and its base is 755 feet wide. Before 1889 when the Eiffel Tower was built in France, the Pyramid of Khufu was the tallest building on earth. The Eiffel Tower is 984 feet tall. What makes the pyramid's design perfect is the way it works against gravity.

³     Buildings and structures are affected by two forces of gravity called compression and tension. Compression is the pushing force against a structure. Tension is the pulling force against a structure. Buildings and bridges must be designed to withstand these constant forces. Think about your desk chair in school. When you sit on your chair, the weight of your body causes the chair seat and back to be in compression or squeezed toward the legs of the chair. So where is the tension? As these areas of the chair are in compression, the braces or supports between the legs are in tension. This means that your weight on the seat pushes on the legs, and the legs pull on the supports. In the case of pyramids, the force of gravity is felt to a greater degree by the base of the pyramid. As gravity pushes on the top of the pyramid, the tension is felt by the base which is much wider than the top. This wide base is the pyramid's strength.

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