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The Shadow Knows (Shadows and Light)

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  • Picture it if you can: You're walking alone down a dimly lit street and for some reason, you start to feel like someone is following you. Quickly you spin around only to see your own shadow behind you. You move further up the street and turn again only this time, even your shadow is gone! Where did it go? What makes shadows change?

    Here's a challenge for you that lets you explore the relationship between shadows and light.

    Here's what you'll need to play along:

    • A new pencil or one that has hardly been used.
    • A Flashlight
    • A stick of modeling clay or can of play dough
    • A dark room

    Begin by placing the lump of clay or play dough on a table top and rolling it into a ball. Place the pencil into the lump point first and adjust it so that it is sticking straight up and down.

    Okay, so here's the challenge question:

    What controls the length of a shadow and what makes a shadow move from one place to another? Make a prediction before you try.

    What You Do

    Turn off all the lights and make the room as dark as possible. Hold the flashlight directly over the top of the pencil so that it is shining straight down. What kind of shadow is produced?

    Now, slowly bring the flashlight down toward the table top making sure that it is still pointing toward the pencil. What kind of shadow do you have now?

    Move the flashlight back and forth across the pencil and see what happens to the shadow. Is there any rule that you can come up with to explain why you get the results you do? Take care and make sure you stay out of the shadows!

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    Notes to Teachers

    Learning Outcomes:

  • Make a prediction based on previous knowledge and explain the reasoning behind that prediction.

  • Experiment with hands-on materials to answer the question: What factors control the length of a shadow?

  • Understand that the angle and position of the light source are the major factors controlling the length and direction of the shadow.

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    Related Web Sites

    For more information about light, try:



    General Science Sites

    Science and Technology for Children Curriculum

    The Natural History Museum (London)

    Edison National Historic Site

    Endangered Species Program

    National Inventors Hall of Fame

    Understanding Our Planet Through Chemistry

    Maps and References

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