Lesson 12
Light and Shadows
Learners explore light as a form of energy, discover why shadows form and change, and find out that almost everything they see is reflected light.

Key Ideas
  • Light is a form of energy that travels in straight lines from its source. Light sources include the sun, fire, light bulbs, and glowing screens. Without a light source, nothing can be seen.
  • Materials interact with light in three ways: OPAQUE materials block all light (wood, brick, your hand); TRANSPARENT materials let all light pass through (clear glass, water, plastic wrap); TRANSLUCENT materials let some light through but scatter it (wax paper, frosted glass, tissue paper).
  • Shadows require three things: a light source, an opaque object, and a surface to catch the shadow. A shadow is simply an absence of light where the object blocked it.
  • The closer the light source, the bigger the shadow. The angle of the light determines the direction and length of the shadow.
  • The sun moves across the sky from east to west throughout the day. In the morning it is low in the east, giving long shadows pointing west. At noon it is high overhead, giving short shadows. In the evening it is low in the west, giving long shadows pointing east.
  • Light bounces off surfaces through a process called reflection. Almost everything we see is reflected light, not light produced by the object itself. The moon is a clear example: it produces no light of its own and is only visible because it reflects sunlight.
  • Digging deeper: sundials use predictable shadow movement to tell time. A pointer called a gnomon casts a shadow that shifts as the sun moves. People used this system for thousands of years before mechanical clocks existed.

Vocabulary

  • Light source: An object that produces its own light, such as the sun, fire, a light bulb, or a glowing screen.
  • Opaque: Describes a material that blocks all light. No light passes through it.
  • Transparent: Describes a material that lets all light pass straight through. You can see clearly through it.
  • Translucent: Describes a material that lets some light through but scatters it. You cannot see clearly through it.
  • Reflection: The bouncing of light off a surface. Almost everything we see is reflected light.
  • Shadow: An area of darkness created when an opaque object blocks light from reaching a surface.
  • Gnomon: The pointer on a sundial that casts a shadow to show the time as the sun moves across the sky.

Discussion Questions
  • If light travels only in straight lines, how does a single lamp in one corner light up an entire room?
  • If the sun suddenly went dark, how long do you think we would still be able to see the moon? What would eventually happen?
  • Why do shadows sometimes have sharp edges and other times have soft, blurry edges?

Supplies
  • A flashlight
  • A small solid opaque object (eraser, small toy, or block)
  • White paper or a light-colored wall

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L12: Distinguishing Living Things from Natural Earth and Human Made by Selene
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