Science Fenns K-5Grades K to 5
A child pushes a wooden block across a sandpaper, a smooth board and a towel, with a ruler beside each.

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Friction Patterns

Surfaces that grip and surfaces that slide.

Lesson 14 of 40

Try this first

Before we start

Today’s story

Friction Patterns

Rosa pushes a box across the barn floor. It slides easily on the smooth concrete. Then it hits a patch of hay. It nearly stops. She has to push much harder.

Friction is a force between two surfaces that touch. It pushes against sliding. Rough surfaces make more friction. Smooth surfaces make less. Friction can make things stop. It also helps you walk without slipping.

The pattern is easy to test. Pull the same object across different surfaces and measure. Rough surfaces need a bigger pull. Slippery ones need a smaller one. Here are the steps.

See it

Five steps. Every time.

    Hands on

    Slide Test

    25 minutes · Do this with a grown-up nearby

    You need

    • A small wooden block or a book
    • A ramp made from a board and books
    • A towel
    • Sandpaper
    • Wax paper
    • Ruler or tape measure
    • Notebook

    Do this

    1. Build a ramp the same height each time.
    2. Cover the ramp with wax paper.
    3. Let the block slide down and measure how far it goes past the ramp.
    4. Repeat three times and write each distance.
    5. Replace the surface with a towel and repeat.
    6. Do the same with sandpaper.
    7. Compare the average distance.
    Write or draw: A table with Surface, three distances in centimeters and the average.

    Watch for: Notice that the smoother surface let the block go farther. Notice that the roughest surface stopped it sooner.

    Safety: Keep the ramp low and hands clear of the sliding block.

    Same every time

    Three rules

    Rule 1Friction works against sliding.

    It slows moving things.

    Rule 2Rough makes more friction.

    Smooth makes less.

    Rule 3Friction is a contact force.

    Surfaces must touch.

    Grandpa Fenn’s notebook

    Say it like a scientist

    friction
    A force that works against sliding between touching surfaces.
    surface
    The outside of an object.
    contact force
    A force that needs touching.
    rough
    Bumpy, not smooth.

    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 a surface has more friction?
    • Where at home or on the ranch do you want more friction, and where less?
    Did you know

    Rubbing your hands together quickly makes them warm. That heat comes from friction.

    Someone who does this

    A tire engineer designs tread to grip wet Texas roads.

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