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Exploring the path light takes and how its movement leads to the creation of shadows.
Have you ever wondered why you can't see around a corner without a mirror? It's because light is like a super-fast runner that refuses to turn left or right!
Light is always on the move, but it follows a very strict rule: it only travels in straight lines. Scientists call these paths rays. Think of a laser pointer; the light doesn't wiggle or curve through the air. It goes directly from the source to the target. This behavior is called rectilinear propagation. Because light cannot curve around objects, we can't see things hidden behind a wall unless the light reflects off something else first. If light could bend like a snake, there would be no such thing as 'hiding'!
Quick Check
If you are standing behind a large tree, why can't the sunlight reach you directly?
Answer
Because light travels in straight lines and cannot curve around the tree trunk to reach you.
A shadow is simply an area where light has been blocked. When light rays hit an opaque object—something solid that light cannot pass through, like your body or a book—the rays are stopped in their tracks. Since the light continues to travel in straight lines past the edges of the object, it creates a dark shape on the surface behind it. The shadow usually looks like a dark version of the object because the light rays that just miss the edges define the shadow's border.
1. Turn on a flashlight in a dark room. 2. Place your hand cm in front of the light. 3. Observe the dark shape on the wall. This is your shadow because your hand is opaque and blocked the straight light rays.
Quick Check
What kind of object is needed to create a clear shadow: transparent (clear) or opaque (solid)?
Answer
An opaque object is needed because it blocks the light rays.
Have you noticed that shadows aren't always the same size? The size of a shadow depends on the distance between the light source, the object, and the surface. When an object is closer to the light source, it blocks a wider angle of light rays, making the shadow larger. As the object moves further away from the light, it blocks fewer rays, and the shadow becomes smaller. We can represent the distance from the light as . If decreases, the shadow size increases!
Imagine you are making a shadow puppet of a bird. 1. Hold your hands cm from the lamp. The bird shadow looks giant on the wall. 2. Move your hands to cm from the lamp. The bird shadow shrinks. 3. This happens because at cm, your hands block more of the light's 'pathway' than at cm.
During a sunset, the Sun is low in the sky. The light rays hit you at a sharp angle. Because the light must travel a longer path past you to hit the ground, your shadow becomes very long. If the Sun is at an angle of above the horizon, your shadow will be much longer than when the Sun is at (directly overhead)!
What is the scientific term for light traveling in straight lines?
If you move a toy closer to a lamp, what happens to its shadow on the wall?
Light can curve around a corner to illuminate a dark hallway.
Review Tomorrow
Tomorrow, try to explain to a friend why your shadow is so long in the late afternoon compared to lunchtime.
Practice Activity
Find a flashlight and three pieces of paper. Cut a small hole in the center of each. Try to align them so you can see the light through all three holes at once. What does this tell you about the path of light?