Light Walks Straight
Rectilinear propagation — and the shadows that prove it
What this lesson covers
Why it matters
Try to peep around a corner without a mirror. You can't — because light refuses to bend around it. Every shadow on the ground is light's confession: I only walk straight.
Predict first
Shadows form because light…
Block a straight-walking traveller and you get a dark patch shaped like the blocker — the shadow is a straight-line proof.
- travels in straight lines and cannot bend around objects — correct
- is afraid of objects
- bends around corners
What you do
Block the lamp with the ball: grow a giant shadow, lose it entirely, and find the soft penumbra rim — eclipse physics on a table.
Check yourself
Which of these makes its OWN light (luminous)?
The Moon and the mirror only pass on borrowed light — the Sun is the lamp.
For a shadow you need a light source, a screen and…
Opaque blocks, transparent passes, translucent blurs — only blocking makes a proper shadow.
A lunar eclipse happens when…
Earth blocks the sunlight, casting a shadow into space — umbra and penumbra, exactly like your ball on the screen, but planet-sized.
- the Sun — correct
- the Moon
- a mirror
- an opaque object (one light can't pass through) — correct
- a transparent object like clear glass
- a mirror
- the Moon passes through the EARTH''s shadow — correct
- the Moon switches off for a night
- clouds cover the Moon