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Why Wet Skin Feels Colder Than the Air

8th grade nonfiction passage about evaporation and cooling: 257 words, six questions, an answer key and vocabulary.

8th grade nonfiction evaporation and cooling 257 words

Why Wet Skin Feels Colder Than the Air

Step out of a swimming pool on a warm, breezy day and you may start to shiver, even though the air is pleasant. Your skin is not colder than before. The shiver comes from water drying on your skin, and drying is a process that takes heat away from whatever is under it.

Water is made of particles that are always moving, but they do not all move at the same speed. Some are quick and some are slow, and the average speed of the group is what we measure as temperature. At the surface of a puddle or a drop, the fastest particles have enough energy to break free and escape into the air as vapor. This escape is called evaporation.

Here is the key idea. When the quickest particles leave, the particles that remain are, on average, slower. The water that is left is therefore cooler. Heat then flows into that cooler water from its surroundings, including your skin, and your skin feels the loss.

Your body uses this effect on purpose. When you get hot, you sweat, and as the sweat evaporates, it carries heat away from your skin. On a very humid day the air already holds a lot of vapor, so sweat dries slowly and the cooling is weak. That is one reason humid heat feels so uncomfortable.

People have used the effect for a very long time. A clay pot lets a little water seep through its walls, and when that water evaporates from the outside, the water inside stays cooler.

Questions

  1. Why might you shiver after leaving a pool on a warm, breezy day? in the text

  2. What is evaporation? in the text

  3. Why is the remaining water cooler after the fastest particles leave? think about it

  4. How does sweating help the body cool down? in the text

  5. Why does humid heat feel so uncomfortable? think about it

  6. How does a clay pot keep the water inside cool? think about it

Words to know

evaporation
when a liquid turns into a gas at its surface
vapor
water in the form of a gas
average
the typical amount found by combining a group
humid
full of moisture in the air
seep
to flow slowly through tiny openings
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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 · 241 words · Flesch-Kincaid grade 3.9

Step out of a pool on a warm, breezy day. You may start to shiver, even though the air is nice. Your skin is not colder than before. The shiver comes from water drying on your skin. Drying takes heat away from whatever is under it.

Water is made of particles that are always moving. They do not all move at the same speed. Some are quick and some are slow. The average speed of the group is what we measure as temperature. At the surface of a puddle or a drop, the fastest particles have enough energy to break free. They escape into the air as vapor. This is called evaporation.

Here is the key idea. When the quickest particles leave, the ones left behind are slower on average. So the water that is left is cooler. Heat then flows into that cooler water from around it, including from your skin. Your skin feels the loss.

Your body uses this on purpose. When you get hot, you sweat. As the sweat evaporates, it carries heat away from your skin. On a very humid day, the air already holds a lot of vapor. Sweat dries slowly, and the cooling is weak. That is one reason humid heat feels so bad.

People have used this effect for a very long time. A clay pot lets a little water seep through its walls. When that water evaporates outside, the water inside stays cooler.

▲ This passage · 257 words · Flesch-Kincaid grade 6.6

Step out of a swimming pool on a warm, breezy day and you may start to shiver, even though the air is pleasant. Your skin is not colder than before. The shiver comes from water drying on your skin, and drying is a process that takes heat away from whatever is under it.

Water is made of particles that are always moving, but they do not all move at the same speed. Some are quick and some are slow, and the average speed of the group is what we measure as temperature. At the surface of a puddle or a drop, the fastest particles have enough energy to break free and escape into the air as vapor. This escape is called evaporation.

Here is the key idea. When the quickest particles leave, the particles that remain are, on average, slower. The water that is left is therefore cooler. Heat then flows into that cooler water from its surroundings, including your skin, and your skin feels the loss.

Your body uses this effect on purpose. When you get hot, you sweat, and as the sweat evaporates, it carries heat away from your skin. On a very humid day the air already holds a lot of vapor, so sweat dries slowly and the cooling is weak. That is one reason humid heat feels so uncomfortable.

People have used the effect for a very long time. A clay pot lets a little water seep through its walls, and when that water evaporates from the outside, the water inside stays cooler.

■ Harder · 270 words · Flesch-Kincaid grade 8.2

Step out of a swimming pool on a warm, breezy day and you may begin to shiver, even though the air is perfectly pleasant. Your skin is not actually colder than it was before. The shiver is caused by water drying on your skin, and drying is a process that draws heat away from whatever lies beneath it.

Water consists of particles that are in constant motion, but they do not all travel at the same speed. Some are quick and some are sluggish, and the average speed of the whole group is what we measure as temperature. At the surface of a puddle or a droplet, the fastest particles possess enough energy to break free and escape into the air as vapor. This escape is known as evaporation.

Here lies the key idea. When the quickest particles depart, the particles that remain are, on average, slower, so the water that is left behind is cooler. Heat then flows into that cooler water from its surroundings, including your skin, and your skin registers the loss.

Your body exploits this effect deliberately. When you overheat, you sweat, and as the sweat evaporates, it carries heat away from your skin. On a very humid day, the air already contains a great deal of vapor, so sweat dries slowly and the cooling is feeble. That is one reason why humid heat feels so oppressive.

People have taken advantage of the effect for a very long time. A clay pot permits a small amount of water to seep through its walls, and when that water evaporates from the outside, the water inside remains cooler.

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 evaporation, vapor, average, humid and seep 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 "Why Wet Skin Feels Colder Than the Air"?

It was written for 8th grade. It has 257 words and works out to a Flesch-Kincaid grade level of about 6.6. 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 six. 3 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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