Why Shadows Change Size
Learners can explain that a shadow's size changes because of the angle between the light source and the object, and the distance from the light source, using the model of straight-line light rays.
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Why does your shadow change size during the day?
- light-rays
- Light travels in straight lines from a source.
- shadow-formation
- A shadow forms where an object blocks straight-line light rays from reaching a surface.
- shadow-size-angle
- Shadows change length as the angle of the light source relative to the object changes. Lower angle → longer shadow.
- shadow-size-distance
- For a fixed angle, moving the light source closer makes the shadow larger; moving it farther makes it smaller.
- combined-effect
- Both angle and distance together determine shadow size in real-world situations.
A shadow is longest when the sun is directly overhead at noon.
Show that a high sun angle (overhead) produces the shortest shadow; a low angle (near horizon) produces the longest shadow.
Moving a light source farther away makes the shadow bigger.
Demonstrate that moving the light source farther actually makes the shadow smaller because the rays become more parallel.
- penumbra and umbra
- multiple light sources
- diffraction and wave nature of light
- mathematical formulas
- Earth's orbit details
- Learner can predict whether a shadow will be longer or shorter when the sun angle changes.
- Learner can explain why a flashlight held close to a hand casts a large diffuse shadow while a distant overhead light casts a sharp small shadow.
- Apply the angle–distance model to explain shadow length changes observed outdoors at different times of day or indoors with artificial lights.
Curious general learners ages 13+ with no prior physics background; comfortable with simple geometry (angles).
- 01Your Changing Shadowslide
- 02Angle & Shadow Lengthinteractive
- 03Light Travels in Straight Linesslide
- 04Ray Diagram Explorerinteractive
- 05Distance Matters Toointeractive
- 06Both Angle and Distanceslide
- 07Shadow Shifterinteractive
- 08Outdoor vs. Indoor Shadowsslide
- 09What About the Object?slide
- 10Check Your Understandingslide
- 11A New Questionslide
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