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Why Bridge Builders Trust Triangles

6th grade nonfiction passage about triangles and strong shapes: 215 words, six questions, an answer key and vocabulary.

6th grade nonfiction triangles and strong shapes 215 words

Why Bridge Builders Trust Triangles

Imagine four wooden sticks joined at the corners with loose bolts to make a rectangle. Push on one corner and the whole frame leans over into a slanted shape called a parallelogram. The sticks have not changed length, but the angles between them have. Now add a fifth stick across two opposite corners. The frame splits into two triangles, and it stops leaning.

A triangle is the one shape that cannot be squeezed out of shape this way. When the three side lengths are fixed, the angles are fixed too, so the triangle holds still unless a stick bends or breaks. Engineers take advantage of this in bridges, roof supports, and tall cranes.

Many bridges use a truss, which is a frame built from rows of triangles. When a heavy truck rolls onto the bridge, the weight does not rest on one beam. Some beams are pressed together, and others are gently stretched. The load spreads out through the whole frame, so no single beam has to do all the work.

Triangles are not magic, and a good bridge still needs strong materials and careful measuring. But the next time you cross a bridge with metal beams in a zigzag pattern, look closely. You are probably looking at triangles, doing a job that rectangles cannot.

Questions

  1. What shape does a pushed rectangle frame turn into? in the text

  2. What does the fifth stick do to the frame? in the text

  3. What is a truss? in the text

  4. Why does a triangle hold its shape? think about it

  5. What happens to the weight of a truck on a truss bridge? in the text

  6. Why does the passage say a good bridge still needs more than triangles? think about it

Words to know

parallelogram
a four sided shape with two pairs of matching sides
angles
the spaces where two lines meet at a corner
engineers
people who design and build useful structures
truss
a bridge or roof frame made of triangles
beam
a long strong piece of wood or metal
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One passage, three levels

The same topic and facts written three ways, so a mixed class can read and talk about one text. Each group’s sheet shows only a shape; the key says which is which.

● Easier · 179 words · Flesch-Kincaid grade 3.2

Picture four wooden sticks joined at the corners with loose bolts. They make a rectangle. Push one corner. The frame leans over into a slanted shape called a parallelogram. The sticks are the same length, but the angles changed. Now add a fifth stick across two opposite corners. The frame becomes two triangles. It stops leaning.

A triangle cannot be squeezed out of shape. When the three sides are fixed, the angles are fixed too. The triangle holds still unless a stick bends or breaks. Engineers use this in bridges, roof supports, and tall cranes.

Many bridges use a truss. A truss is a frame made of rows of triangles. When a heavy truck drives onto the bridge, the weight does not sit on one beam. Some beams are pressed together. Others are gently stretched. The weight spreads out, so no one beam does all the work.

Triangles are not magic. A good bridge still needs strong materials and careful measuring. But look for the zigzag of metal beams on a bridge. You are looking at triangles at work.

▲ This passage · 215 words · Flesch-Kincaid grade 5.8

Imagine four wooden sticks joined at the corners with loose bolts to make a rectangle. Push on one corner and the whole frame leans over into a slanted shape called a parallelogram. The sticks have not changed length, but the angles between them have. Now add a fifth stick across two opposite corners. The frame splits into two triangles, and it stops leaning.

A triangle is the one shape that cannot be squeezed out of shape this way. When the three side lengths are fixed, the angles are fixed too, so the triangle holds still unless a stick bends or breaks. Engineers take advantage of this in bridges, roof supports, and tall cranes.

Many bridges use a truss, which is a frame built from rows of triangles. When a heavy truck rolls onto the bridge, the weight does not rest on one beam. Some beams are pressed together, and others are gently stretched. The load spreads out through the whole frame, so no single beam has to do all the work.

Triangles are not magic, and a good bridge still needs strong materials and careful measuring. But the next time you cross a bridge with metal beams in a zigzag pattern, look closely. You are probably looking at triangles, doing a job that rectangles cannot.

■ Harder · 235 words · Flesch-Kincaid grade 7.9

Imagine four wooden sticks fastened at their corners with loose bolts so that they form a rectangle. If you push on one corner, the entire frame leans over into a slanted shape known as a parallelogram. The sticks have not changed in length, yet the angles between them have shifted. Now fasten a fifth stick diagonally across two opposite corners. The frame divides into two triangles, and it no longer leans at all.

A triangle is the one shape that cannot be squeezed out of form in this manner. Once its three side lengths are fixed, its angles are fixed as well, so the triangle holds steady unless one of its sticks bends or snaps. Engineers take advantage of this property in bridges, roof supports, and towering cranes.

Many bridges are built on a truss, which is a framework assembled from rows of triangles. When a heavy truck rolls onto the bridge, its weight does not rest on any single beam. Some beams are pressed together while others are gently stretched, and the load is distributed throughout the whole frame, so that no one beam must carry the burden alone.

Triangles are not magical, and a sound bridge still demands strong materials and careful measuring. Even so, the next time you cross a bridge whose metal beams form a zigzag pattern, look closely. You are very likely seeing triangles performing a task that rectangles cannot.

Download as one PDF

How to use it

  1. Press Read it big (or B) to put the text on the projector, or Full screen (F) to fill the whole screen.
  2. Ask the questions one at a time and use Show answer when the class has decided. A shows or hides every answer.
  3. Print student copy for the class, or Print with answers for yourself.

Ideas for class

  • Before reading, put parallelogram, angles, engineers, truss and beam on the board with their meanings from the Words to know section and have students predict what the text will be about.
  • Read it aloud once while students follow along, then have them reread it alone or with a partner. At a calm 100 words a minute it takes about 2 minutes to read aloud.
  • Use the Read it big button (or B) to put the text on the projector, and Show answer on one question at a time so the class commits to an answer first.
  • Question 4 asks the reader to infer. Ask students to point to the words in the passage that led them to their answer.
  • Ask students to write one question the passage did not answer, then look for the answer in a book or on a classroom screen.
  • Print the student copy for independent work and keep the answer-key copy for yourself.

Related

Questions

What reading level is "Why Bridge Builders Trust Triangles"?

It was written for 6th grade. It has 215 words and works out to a Flesch-Kincaid grade level of about 5.8. That is a formula's estimate from sentence length and syllables, and it is not a Lexile or a guided reading level, so check it against your students.

What do the questions ask?

There are six. 4 ask for something the text says directly and 2 ask the reader to work something out from clues. Each has an answer in the key, and the answers are written as a teacher would accept them, not as the only possible wording.

How long does it take to read?

About 2 minutes read aloud at 100 words a minute. For a one-minute fluency check, paste it into the fluency timer and use the word count.

Can I print it?

Yes. Print student copy gives the passage, the questions with lines to write on, and the word meanings. Print with answers gives the same page with the answers filled in. Both are made in your browser.

Is this passage from a published book?

No. It was written for Peabody Teach, so there is no book to buy and no login to read it.

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