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  • Squeaks and I were out on a walk this morning, and we both noticed lots of things are changing!

  • We found leaves that had changed color and fallen to the ground, and we saw birds flying

  • south for the winter.

  • What else did you observe, Squeaks?

  • [Squeaks squeaks]

  • Squeaks says that he found something all over the plants this morning, something frozen

  • and sparkling.

  • Hmm.

  • Was it cold, and just lightly covering the plants?

  • [Squeaks squeaks]

  • Squeaks, it sounds like you found frost.

  • That's a layer of ice that can freeze over things like plants, windows, and even spiderwebs.

  • It only happens at certain times of the year, and it can be a special treat that shows us

  • our seasons in action.

  • During fall and spring, the weather is changing from hot to cold, or from cold to hot, which

  • is perfect for frost.

  • During the day, temperatures are warm enough that the air can hold onto a bit of water

  • vapor, which is water that's spread out through the air as an invisible gas.

  • But then, as night falls and the air gets colder, the gas turns into liquid water again.

  • That's why sometimes when you go outside in the morning the grass is wet, even if it

  • hasn't rained.

  • The water on the grass actually comes from the air.

  • There's a special name for when water in the air turns into a liquid like this.

  • It's called condensation.

  • The water vapor touching things like grass or windows condenses, leaving tiny drops of

  • water over everything.

  • If it's only a little cold, the water on the grass will stay the way it is, making

  • the ground and plants a bit wet in the morning.

  • But when the weather is just right, which is when it's warm during the day and can

  • get very cold at night, the water changes one more time: it freezes into ice!

  • That ice is what we call frost, and it happens when the temperature at night is below 0 degrees

  • Celsius, or 32 degrees Fahrenheit.

  • Frost usually won't make ice over the entire surface of a leaf it freezes on.

  • Instead, water freezes in the shape of the small drops it first made, so it looks like

  • little delicate freckles of ice polka-dotting the whole leaf.

  • Once morning comes, you can walk outside and see beautiful, frozen frost on everything.

  • It can sparkle in the bright sunlight, but it won't last for long.

  • What do you think will happen to the frost, Squeaks?

  • [Squeaks squeaks]

  • That's a good observation, Squeaks.

  • It does look like the frost just disappears.

  • But the frost is actually changing again.

  • Later in the morning, as the sun warms up the space around it, the frost starts to melt.

  • The ice might turn back into liquid water, or if it warms up enough very quickly, it

  • can even turn right back into water vapor in the air.

  • Sometimes, you can even see the water vapor rising right off of the ground.

  • It looks just like a thick fog coming up.

  • Frost can be beautiful to see, and it's usually a sign that the seasons and weather

  • are changing.

  • When we're going from the warm summer to the cold winter, frost means fall is here,

  • and the air and soil are about to get very chilly.

  • People who grow plants, like farmers and gardeners, pay very close attention to the temperatures

  • in fall to help keep their plants from freezing in the morning frost.

  • Some farmers that work in places where there's lots of frost need to make sure to pick all

  • of their crops before fall gets too cold.

  • They'll check things like how much water is in the air, the temperature during the

  • day and at night, and how fast the wind is going, all so they can know when the first

  • big frost of the year will happen.

  • It's like they're water scientists!

  • You can be a frost-watching expert, too!

  • You could try checking the weather before bed to see how cold it will get during the

  • night, and guess whether there might be frost in the morning.

  • Is the air above freezing before bed, but going to drop down below freezing overnight?

  • Is it humid, with lots of water vapor in the air?

  • Make your guess, then look at the ground outside the next morning to see if you were right!

  • [Squeaks squeaks]

  • Sure, we can try it tonight, Squeaks!

  • We'll make a field journal where we can write everything down to keep track.

  • If you try this, too, Squeaks and I would love to hear about what you learned!

  • Just ask a grown-up to help you go to our website at, where

  • you can tell us about your results.

  • Thanks, and we'll see you next time here at the Fort!

Squeaks and I were out on a walk this morning, and we both noticed lots of things are changing!


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B1 中級

It's Time for Frost!

  • 2 1
    joey joey に公開 2021 年 05 月 09 日