Science Fenns K-5Grades K to 5
A cold glass of lemonade on a porch table with drops of water on the outside, and a kettle steaming in the background.

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Boiling and Condensing

Where does the water on a cold glass come from?

Lesson 12 of 41

Try this first

Before we start

Today’s story

Boiling and Condensing

Pat gets a glass from the freezer. It is cold. In the warm kitchen, tiny drops form on it. Soon it is wet all over.

Water is in the air as a gas. It is called water vapor. When vapor touches something cold, it cools and turns into liquid. That is condensation.

Heat can do the opposite too. A pot on the stove makes bubbles, then steam. That is boiling. The steps explain both.

See it

Five steps. Every time.

    Hands on

    Drops on a cold cup

    20 minutes · Do this with a grown-up nearby

    You need

    • Two clear cups
    • Ice water
    • Room-temperature water
    • Paper towel
    • Paper
    • Pencil

    Do this

    1. Fill one cup with ice water and one with room-temperature water.
    2. Predict which one gets drops.
    3. Wait five minutes.
    4. Look at the outside of each cup.
    5. Draw what you see.
    6. Wipe a spot and watch it again.
    7. Write why you think it happened.
    Write or draw: A drawing of each cup and your explanation.

    Watch for: Notice the drops only form on the cold cup.

    Safety: Do not use a stove or hot water. An adult handles any boiling.

    Same every time

    Three rules

    Rule 1Boiling needs a lot of heat.

    Warm water is not boiling.

    Rule 2Condensing needs cooling.

    The vapor loses heat.

    Rule 3The water is still water.

    Only the state changes.

    Grandpa Fenn’s notebook

    Say it like a scientist

    boiling
    When a hot liquid turns into a gas with bubbles.
    condensation
    When a gas cools and becomes a liquid.
    water vapor
    Water as an invisible gas in the air.

    Poppy’s quiz

    Six questions

    Tap an answer. Green means right. You will see why.

    Talk about it

    Say it out loud

    • What happened on the cold cup? How do you know where the drops came from?
    • Where do you see condensation at home, like a bathroom mirror?
    Did you know

    A cloud is made of tiny drops of water that condensed from the air.

    Someone who does this

    A meteorologist studies water vapor and clouds to predict storms.

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