Science Fenns K-5Grades K to 5
A flashlight beam crossing a dusty room in a straight bright line and casting a dark shadow of a hand on the wall.

Science / All lessons / Energy, Circuits and Light

Light Travels Straight

Shadows and beams.

Lesson 21 of 41

Try this first

Before we start

Today’s story

Light Travels Straight

Sunbeams slant through a barn door. Dust shows them off. They run in straight lines.

Light travels in straight lines until it hits something. That is why you can aim a beam and why a hand makes a shadow. A shadow is a place where light is blocked.

Let us test it with a card and a flashlight. Three cards will show the path of a beam. Here are the steps.

See it

Five steps. Every time.

    Hands on

    Three Cards

    20 minutes · Do this with a grown-up nearby

    You need

    • Three index cards
    • Pencil
    • Clay or tape
    • Flashlight
    • Dark room
    • Ruler

    Do this

    1. Poke a hole in the center of each card.
    2. Stand them upright in a row with clay.
    3. Shine the flashlight through the first hole.
    4. Look for the light spot on a wall.
    5. Slide the middle card sideways.
    6. Draw what happened.
    Write or draw: A drawing of the cards with the beam shown as a line.

    Watch for: When does the light get through? What does that say about its path?

    Safety: Do not shine the light at eyes.

    Same every time

    Three rules

    Rule 1Light moves in straight lines

    This helps you predict.

    Rule 2A shadow needs three things

    Light, an object and a surface.

    Rule 3Test with a fair setup

    Keep distances the same.

    Grandpa Fenn’s notebook

    Say it like a scientist

    shadow
    A dark area where light is blocked.
    beam
    A narrow stream of light.
    opaque
    Blocking light completely.
    source
    Where light begins.

    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 light travels straight?
    • Where do you see shadows at home or on the farm?
    Did you know

    Light from the Sun takes about eight minutes to reach Earth.

    Someone who does this

    A photographer uses light and shadow to make pictures.

    BeforeCircuit OutputsNext lessonReflect, Refract, Absorb