Teaching: Keep it cold: an insulation test
Start with this
A wool sock keeps your foot warm. So could that same sock keep an ice cube from melting? Something sneaky is going on with heat, and we get to test it.
Read this together, 171 words
A Bottle That Keeps Things Hot or Cold
In 1892, a Scottish scientist named James Dewar had a problem. He was studying gases, like the oxygen in the air, that he had cooled until they turned into liquids. Those liquids were far colder than anything in a freezer, and heat from the warm room kept rushing in and boiling them away.
So Dewar made a new kind of bottle. He put one glass bottle inside another and joined them at the neck. Then he pumped the air out of the space between the two walls. With almost no air in that gap, heat had a very hard time getting across, and his cold liquids lasted much longer.
Dewar never patented his bottle. A few years later, a company in Germany began making bottles the same way and selling them under the name Thermos. Today the same kind of bottle keeps soup hot at lunchtime and lemonade cold on a summer day. It does not make heat or cold. It slows heat from moving through its walls, in either direction.
Tell June, 1 of 6
Heat always moves from warmer things to cooler things.
An ice cube sitting on the counter melts because heat moves into it from the warmer air around it. The ice does not melt because of anything it does by itself. Heat is flowing in, a little at a time.
Tell June, 2 of 6
Heat also needs something to travel through, like air or a solid material.
That is why "A Bottle That Keeps Things Hot or Cold" matters. In the bottle's gap, almost nothing was left to carry heat across, so the heat had a very hard time getting through.
Tell June, 3 of 6
A good insulator slows heat down.
Some materials are the opposite. Metals, like aluminum foil, are conductors, which means they let heat move through them quickly.
Tell June, 4 of 6
A coat or a blanket does not make heat.
It slows the heat that is moving out of your body, so you stay warm. Wrapped around an ice cube, the same wool slows heat moving in, so the ice stays frozen longer. Insulators never make anything cold. They only slow heat down, in either direction.
Tell June, 5 of 6
A scientist can compare wrappings with a fair test.
Use ice cubes of the same size, the same kind of bags, the same spot, and the same amount of time. Change only the wrapping. Then if the results differ, the wrapping must be the reason.
Tell June, 6 of 6
Measuring turns "more" and "less" into numbers.
After the wait, count the teaspoons of melted water from each bag. Fewer teaspoons means less ice melted, so the wrapping slowed heat better. Here is a finished example with pretend numbers: the sock bag made 2 teaspoons and the bare bag made 7 teaspoons. The sock slowed heat more, so it goes ahead of the bare bag in the order from best insulator to worst.
Do it together, 1 of 4
Go back to the second paragraph of "A Bottle That Keeps Things Hot or Cold", the part about pumping the air out of the space between the two walls.
Ask June how heat gets from a warm room to something cold, and what it would need to travel through. Let June talk it through, then ask why an almost empty gap would be so hard for heat to cross.
A Bottle That Keeps Things Hot or Cold
In 1892, a Scottish scientist named James Dewar had a problem. He was studying gases, like the oxygen in the air, that he had cooled until they turned into liquids. Those liquids were far colder than anything in a freezer, and heat from the warm room kept rushing in and boiling them away.
So Dewar made a new kind of bottle. He put one glass bottle inside another and joined them at the neck. Then he pumped the air out of the space between the two walls. With almost no air in that gap, heat had a very hard time getting across, and his cold liquids lasted much longer.
Dewar never patented his bottle. A few years later, a company in Germany began making bottles the same way and selling them under the name Thermos. Today the same kind of bottle keeps soup hot at lunchtime and lemonade cold on a summer day. It does not make heat or cold. It slows heat from moving through its walls, in either direction.
Do it together, 2 of 4
Hold up the aluminum foil, the sock, and the newspaper or paper towels one at a time.
Let June crumple, squeeze, and feel each one. Ask what June notices about how thick each is and whether it feels like it holds air. Ask June to remember that foil is a metal and to say what that might mean for heat.
A Bottle That Keeps Things Hot or Cold
In 1892, a Scottish scientist named James Dewar had a problem. He was studying gases, like the oxygen in the air, that he had cooled until they turned into liquids. Those liquids were far colder than anything in a freezer, and heat from the warm room kept rushing in and boiling them away.
So Dewar made a new kind of bottle. He put one glass bottle inside another and joined them at the neck. Then he pumped the air out of the space between the two walls. With almost no air in that gap, heat had a very hard time getting across, and his cold liquids lasted much longer.
Dewar never patented his bottle. A few years later, a company in Germany began making bottles the same way and selling them under the name Thermos. Today the same kind of bottle keeps soup hot at lunchtime and lemonade cold on a summer day. It does not make heat or cold. It slows heat from moving through its walls, in either direction.
Do it together, 3 of 4
Give June paper and a pencil to draw a table with four rows and two columns.
The columns are wrapping and teaspoons of melted water. Label the rows bare, foil, sock, and newspaper or paper towels. Then choose the ice cubes together: June hunts for the cubes that look the same size, and you pick a spot on the counter away from any sunny window.
A Bottle That Keeps Things Hot or Cold
In 1892, a Scottish scientist named James Dewar had a problem. He was studying gases, like the oxygen in the air, that he had cooled until they turned into liquids. Those liquids were far colder than anything in a freezer, and heat from the warm room kept rushing in and boiling them away.
So Dewar made a new kind of bottle. He put one glass bottle inside another and joined them at the neck. Then he pumped the air out of the space between the two walls. With almost no air in that gap, heat had a very hard time getting across, and his cold liquids lasted much longer.
Dewar never patented his bottle. A few years later, a company in Germany began making bottles the same way and selling them under the name Thermos. Today the same kind of bottle keeps soup hot at lunchtime and lemonade cold on a summer day. It does not make heat or cold. It slows heat from moving through its walls, in either direction.
Do it together, 4 of 4
Have June decide how to put the wrappings in order afterward, and say it back to you: which number is best, and which is worst.
When June is ready, move on to the activity.
A Bottle That Keeps Things Hot or Cold
In 1892, a Scottish scientist named James Dewar had a problem. He was studying gases, like the oxygen in the air, that he had cooled until they turned into liquids. Those liquids were far colder than anything in a freezer, and heat from the warm room kept rushing in and boiling them away.
So Dewar made a new kind of bottle. He put one glass bottle inside another and joined them at the neck. Then he pumped the air out of the space between the two walls. With almost no air in that gap, heat had a very hard time getting across, and his cold liquids lasted much longer.
Dewar never patented his bottle. A few years later, a company in Germany began making bottles the same way and selling them under the name Thermos. Today the same kind of bottle keeps soup hot at lunchtime and lemonade cold on a summer day. It does not make heat or cold. It slows heat from moving through its walls, in either direction.
Make something together
Ice cube test.
Put one ice cube in each of four zip-top bags and seal them; pick cubes that look the same size. Leave one bag bare. June wraps the others: one in aluminum foil, one in a wool or thick sock, and one in several layers of newspaper or paper towels. Set all four side by side on a plate on the counter, away from sunny windows. Before starting, June predicts which ice cube will melt least. Wait 20 minutes, and do worksheet questions 1, 2, 4, 5, and 6 while you wait. Then unwrap each bag, compare the ice left inside, and June counts how many teaspoons of melted water each bag made, pouring carefully. June writes the counts in a table and puts the wrappings in order from best insulator to worst. Then June answers worksheet question 3.
- four ice cubes
- four zip-top bags
- aluminum foil
- a wool or thick sock
- newspaper or paper towels
- a plate
- a teaspoon
- a clock or phone timer
- paper
- a pencil
Tip If June gets stuck on why a wrapping helps, bring it back to the sock and ask whether it makes heat or only slows it. If June races ahead, ask for a guess of how many teaspoons each bag will make, then compare the guesses to the real counts. Keep the pouring slow and careful, and let June do the counting.
On paper
Insulation Test
4 problems. In your own lessons you print it from here, with an answer key for you.
That’s the lesson
Then you mark it done
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