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Inertia and Seat Belts

7th grade nonfiction passage about motion and forces: 315 words, seven questions, an answer key and vocabulary.

7th grade nonfiction motion and forces 315 words

Inertia and Seat Belts

A car is traveling down the road when the driver slams on the brakes. The car stops quickly, but the people inside seem to lurch forward. Why? The answer is a property of all matter, which scientists call inertia.

Inertia is the tendency of an object to keep doing what it is already doing. An object at rest stays at rest, and an object in motion keeps moving in a straight line at the same speed, unless a force acts on it. This idea is Newton's first law of motion. Inertia is not a force. It is a property that every object has, and the more mass an object has, the more inertia it has.

When a car is moving, everything inside it is moving at the same speed, including you. When the brakes act on the car, a force slows the car down. But no force has yet acted on your body. So your body keeps moving forward at the old speed, even though the car is slowing. It is not that something throws you forward; you are simply continuing to move at the speed you already had.

A seat belt supplies the missing force. It is made of strong, slightly stretchy webbing, and it crosses the strongest parts of the human body, which are the hips and the chest. As the car slows, the belt pulls you back and slows you down along with the car. It does this over a little more time and distance than a hard surface would. A longer stop means a smaller force on your body at any moment.

Inertia explains other ordinary events as well. When a bus pulls away from a stop, you feel pushed back in your seat, because your body tends to stay at rest. When a bus turns a corner, passengers lean to the side, because their bodies want to keep going straight.

Questions

  1. What is inertia? in the text

  2. What is Newton's first law of motion, as the passage describes it? in the text

  3. Why do the people in a car lurch forward when the driver slams on the brakes? in the text

  4. What does a seat belt do? in the text

  5. Why does a longer stop mean a smaller force on your body? think about it

  6. Is it correct to say that something throws you forward when a car stops suddenly, and why or why not? think about it

  7. Why do you feel pushed back in your seat when a bus pulls away from a stop? think about it

Words to know

inertia
the tendency of an object to keep doing what it is already doing
force
a push or a pull on an object
motion
the act of moving from one place to another
lurch
to move suddenly and unsteadily
webbing
strong woven strips of fabric, such as in a seat belt

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 inertia, force, motion, lurch and webbing 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 5 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 "Inertia and Seat Belts"?

It was written for 7th grade. It has 315 words and works out to a Flesch-Kincaid grade level of about 5.6. 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 seven. 4 ask for something the text says directly and 3 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.

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