Skip to the content
Peabody TeachFor teachers and grown-ups

The Gaps That Keep Bridges From Buckling

8th grade nonfiction passage about heat and expansion: 261 words, six questions, an answer key and vocabulary.

8th grade nonfiction heat and expansion 261 words

The Gaps That Keep Bridges From Buckling

Drive across a large bridge and you may feel a quick thump as the tires pass over a strip of metal teeth set into the road. Those teeth are an expansion joint, and the bridge could not survive for long without them, because their purpose is to make room for a change that is invisible to us: nearly everything grows a little larger when it is warmed.

The explanation lies in the particles that make up matter. In a solid, the particles are held in place, but they are never perfectly still, and they jiggle back and forth. When the solid is heated, the jiggling grows wider, and each particle needs a little more room, so that, added together across millions of particles, the whole object grows. Cooling does the opposite, and the object shrinks.

The change is small, but a long steel bridge is enormous, so even a tiny fraction of its length adds up to a noticeable amount, and a bridge deck can be longer on a hot afternoon than on a freezing night. If the ends were fixed tightly, the steel would push hard against its supports, and that force could crack concrete or bend the metal.

Engineers solve the problem by leaving gaps and covering them with interlocking teeth that slide past each other as the bridge grows and shrinks. The same idea appears in many places. Concrete sidewalks have grooves so that cracks form along planned lines, and long pipes often include bends that can flex. Good builders do not fight heat. They plan for it.

Questions

  1. What is the strip of metal teeth in the road called? in the text

  2. What happens to the particles in a solid when it is heated? in the text

  3. Why does a heated object grow larger? think about it

  4. What could happen if a bridge's ends were fixed tightly? in the text

  5. Why might a bridge be longer on a hot afternoon than on a cold night? think about it

  6. What do concrete sidewalks have that is a similar idea to expansion joints? in the text

Words to know

expansion
growing larger in size
joint
a place where two parts meet
particles
the tiny pieces that make up all matter
interlocking
fitting together like the fingers of two hands
engineers
people who design and build things using science
Share

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 · 213 words · Flesch-Kincaid grade 3

Drive across a big bridge. You may feel a quick thump as the tires cross a strip of metal teeth in the road. The teeth are called an expansion joint. The bridge needs them. They make room for a change we cannot see. Nearly everything grows a little larger when it warms up.

The reason is in the particles that make up matter. In a solid, the particles stay in place, but they jiggle back and forth. When the solid is heated, they jiggle more widely. Each particle needs a little more room. Across millions of particles, the whole object grows. When it cools, it shrinks.

The change is small. But a steel bridge is very long, so a small part of its length adds up. A bridge can be longer on a hot afternoon than on a freezing night. If its ends were fixed tightly, the steel would push hard on its supports. That force could crack concrete or bend metal.

Engineers leave gaps. They cover the gaps with teeth that slide past each other as the bridge grows and shrinks. The same idea is used in other places. Concrete sidewalks have grooves, so cracks form along planned lines. Long pipes often have bends that can flex. Good builders plan for heat.

▲ This passage · 261 words · Flesch-Kincaid grade 8.2

Drive across a large bridge and you may feel a quick thump as the tires pass over a strip of metal teeth set into the road. Those teeth are an expansion joint, and the bridge could not survive for long without them, because their purpose is to make room for a change that is invisible to us: nearly everything grows a little larger when it is warmed.

The explanation lies in the particles that make up matter. In a solid, the particles are held in place, but they are never perfectly still, and they jiggle back and forth. When the solid is heated, the jiggling grows wider, and each particle needs a little more room, so that, added together across millions of particles, the whole object grows. Cooling does the opposite, and the object shrinks.

The change is small, but a long steel bridge is enormous, so even a tiny fraction of its length adds up to a noticeable amount, and a bridge deck can be longer on a hot afternoon than on a freezing night. If the ends were fixed tightly, the steel would push hard against its supports, and that force could crack concrete or bend the metal.

Engineers solve the problem by leaving gaps and covering them with interlocking teeth that slide past each other as the bridge grows and shrinks. The same idea appears in many places. Concrete sidewalks have grooves so that cracks form along planned lines, and long pipes often include bends that can flex. Good builders do not fight heat. They plan for it.

■ Harder · 273 words · Flesch-Kincaid grade 12.2

Drive across a large bridge and you may feel a sudden thump as your tires pass over a strip of metal teeth set into the roadway. Those teeth form an expansion joint, and the bridge could not last long without them. Their purpose is to make room for a change that is invisible to ordinary observers, because nearly everything grows slightly larger whenever it is warmed.

The reason lies in the particles that make up matter. In a solid, the particles are held in position, yet they are never perfectly still, and they jiggle constantly back and forth; when the solid is heated, the jiggling becomes wider, so each particle requires a little more room, and, added together across millions upon millions of particles, the entire object grows. Cooling has precisely the opposite effect, and the object shrinks.

The change is small, but a long steel bridge is enormous, so even a tiny fraction of its length adds up to a noticeable amount, and a bridge deck can be considerably longer on a hot afternoon than on a freezing night. If its ends were fixed rigidly, the steel would press hard against its supports, and the resulting force could crack concrete or bend metal.

Engineers solve the problem by leaving gaps and covering them with interlocking teeth that slide past one another as the bridge grows and shrinks, and the same idea appears in many other places, since concrete sidewalks are cut with grooves so that cracks will form along planned lines, and long pipes frequently include bends that are able to flex. Skilled builders do not fight heat; they plan for it.

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 expansion, joint, particles, interlocking and engineers 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 3 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 3 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 "The Gaps That Keep Bridges From Buckling"?

It was written for 8th grade. It has 261 words and works out to a Flesch-Kincaid grade level of about 8.2. 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 3 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.

Nothing you do here is sent to us. No sign-in, no ads.