Science Fenns K-5Grades K to 5
A child builds a small model of a river from sand in a baking pan, next to a sketch of a real river on paper.

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Models That Work

Build one. Say what it shows. Say what it hides.

Lesson 5 of 40

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Before we start

Today’s story

Models That Work

Leo wants to know how a river carves a bank. He cannot sit by the Brazos for a year. So he fills a pan with sand and tilts it. He pours water at the top. A small channel forms. It looks like a tiny river.

That pan is a model. A model is a copy that helps you think. It can be a drawing, a map, a small build or a set of numbers. Models show some parts of the real thing. They also hide some parts. Leo's pan shows that water cuts a path. It does not show the real size or the fish.

A good model fits its job. You can judge it with a few questions. Here are the steps.

See it

Five steps. Every time.

    Hands on

    Bridge Builder Model

    30 minutes · Do this with a grown-up nearby

    You need

    • Index cards or paper
    • Tape
    • Two stacks of books
    • Small coins or paper clips
    • A ruler
    • Notebook

    Do this

    1. Set two book stacks 20 centimeters apart.
    2. Make a bridge from one index card and tape.
    3. Add coins until the bridge sags or falls.
    4. Write how many coins it held.
    5. Fold the card into a pleat and test again.
    6. Compare the two results.
    7. List what your model shows and what it hides.
    Write or draw: A table of design, coins held, and notes. Add a line for what the model hides.

    Watch for: Notice how folding changed strength. Notice that a paper bridge does not behave like a steel one.

    Safety: Keep coins and books off the floor edge and do not stand on the books.

    Same every time

    Three rules

    Rule 1A model has a job.

    Pick the job before you build.

    Rule 2Every model leaves things out.

    That is how it stays simple.

    Rule 3Judge it by its job.

    Ask if it does what you need.

    Grandpa Fenn’s notebook

    Say it like a scientist

    model
    A copy or picture that helps explain how something works.
    prototype
    A first test version of something you build.
    criteria
    Rules you use to judge how good something is.
    limit
    A way a model does not match the real thing.

    Poppy’s quiz

    Six questions

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

    Talk about it

    Say it out loud

    • How do you know your model is a good one?
    • What kind of model do you see at home or at the feed store?
    Did you know

    Engineers test small bridge models in labs before they build the real bridge.

    Someone who does this

    A civil engineer builds and tests models before building a bridge.

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