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Blocking Three Escape Routes for Heat in a Flask

8th grade nonfiction passage about heat transfer in a vacuum flask: 264 words, six questions, an answer key and vocabulary.

8th grade nonfiction heat transfer in a vacuum flask 264 words

Blocking Three Escape Routes for Heat in a Flask

A good vacuum flask can keep soup hot through a long morning and keep water cold through a hot afternoon, but it does not make heat or cold. It only slows the trip that heat takes from a warm place to a cooler one. Heat is always on the move, and it has three different ways to travel, all of which a well-built flask manages to block.

The first way is conduction, in which heat passes from particle to particle through a solid or a liquid, like a message passed along a line of people. The second is convection, in which warmer fluid itself moves and carries heat with it, as when warm air rises from a heater. The third is radiation, in which heat travels as invisible waves that need no material to cross.

A flask is really two containers, one inside the other, joined only at the neck. Almost all the air has been pumped out of the gap between them, which leaves a vacuum, and because a vacuum has very few particles, heat has almost nothing to hand itself along, so conduction is stopped. With no air in the gap, there is also no moving air, so convection is stopped as well.

Radiation can still cross empty space, so the inner wall has a shiny, mirror-like coating. A shiny surface reflects heat waves back instead of letting them pass. The weak spot of a flask is its stopper, because heat can creep through the neck and the lid. That is why a flask loses heat slowly rather than never.

Questions

  1. What are the three ways heat can travel? in the text

  2. How is a flask built to include an empty gap? in the text

  3. Why does a vacuum stop conduction? think about it

  4. What stops convection in a flask? in the text

  5. Why is the inner wall shiny? think about it

  6. Why does a flask lose heat slowly rather than never? in the text

Words to know

conduction
heat passing from one particle to the next
convection
heat carried along by moving air or liquid
radiation
heat that travels in waves through space
vacuum
a space with almost no air or matter in it
stopper
a plug or lid that closes the opening of a bottle
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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 · 234 words · Flesch-Kincaid grade 3.6

A good vacuum flask can keep soup hot all morning. It can keep water cold all afternoon. It does not make heat or cold. It only slows the trip that heat takes from a warm place to a cooler one. Heat is always on the move, and it has three ways to travel. A good flask blocks all three.

The first way is conduction. Heat passes from particle to particle through a solid or a liquid, like a message passed along a line of people. The second is convection. Warm fluid moves and carries heat with it, like warm air rising from a heater. The third is radiation. Heat travels as invisible waves that need no material to cross.

A flask is really two containers, one inside the other. They are joined only at the neck. Almost all the air has been pumped out of the gap between them. This leaves a vacuum. A vacuum has very few particles, so heat has almost nothing to pass itself along. Conduction is stopped. With no air in the gap, no air can move either. Convection is stopped too.

Radiation can still cross empty space. So the inner wall has a shiny, mirror-like coating. A shiny surface reflects heat waves back. The weak spot is the stopper. Heat can creep through the neck and the lid. That is why a flask loses heat slowly, not never.

▲ This passage · 264 words · Flesch-Kincaid grade 8.1

A good vacuum flask can keep soup hot through a long morning and keep water cold through a hot afternoon, but it does not make heat or cold. It only slows the trip that heat takes from a warm place to a cooler one. Heat is always on the move, and it has three different ways to travel, all of which a well-built flask manages to block.

The first way is conduction, in which heat passes from particle to particle through a solid or a liquid, like a message passed along a line of people. The second is convection, in which warmer fluid itself moves and carries heat with it, as when warm air rises from a heater. The third is radiation, in which heat travels as invisible waves that need no material to cross.

A flask is really two containers, one inside the other, joined only at the neck. Almost all the air has been pumped out of the gap between them, which leaves a vacuum, and because a vacuum has very few particles, heat has almost nothing to hand itself along, so conduction is stopped. With no air in the gap, there is also no moving air, so convection is stopped as well.

Radiation can still cross empty space, so the inner wall has a shiny, mirror-like coating. A shiny surface reflects heat waves back instead of letting them pass. The weak spot of a flask is its stopper, because heat can creep through the neck and the lid. That is why a flask loses heat slowly rather than never.

■ Harder · 274 words · Flesch-Kincaid grade 8.2

A well-made vacuum flask can keep soup steaming through a long morning and keep water icy through a sweltering afternoon. It does not manufacture heat or cold. Its only accomplishment is to slow the journey that heat makes from a warm place to a cooler one. Heat is always on the move, and it has three different ways of traveling, all of which a carefully built flask manages to block.

The first way is conduction, in which heat passes from particle to particle through a solid or a liquid, rather like a message handed along a line of people. The second is convection, in which warmer fluid itself moves and carries heat along with it, as when warm air rises from a heater. The third is radiation, in which heat travels as invisible waves that require no material to cross.

A flask is really two containers, one nested inside the other and joined only at the neck. Nearly all of the air has been pumped out of the gap between them, which leaves a vacuum. A vacuum contains very few particles, so heat has almost nothing to hand itself along, and conduction is halted. Without air in the gap, there is also no moving air, so convection is halted as well.

Radiation can still cross empty space, which is why the inner wall carries a shiny, mirror-like coating. A shiny surface reflects heat waves back instead of allowing them to pass through. The weakest point of a flask is its stopper, because heat can creep through the neck and the lid. That is why a flask loses heat slowly, rather than never.

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 conduction, convection, radiation, vacuum and stopper 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 "Blocking Three Escape Routes for Heat in a Flask"?

It was written for 8th grade. It has 264 words and works out to a Flesch-Kincaid grade level of about 8.1. 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.

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