Light & shadows
The idea
Light comes from sources like the sun, lamps, candles, and flashlights, and it travels away from them in straight lines. You see things when light bounces off them and reaches your eyes. A shadow appears when something blocks the light: behind the blocker there is a patch the light cannot reach, and that dark patch is the shadow. That is why your shadow copies your shape — it is the outline of exactly the light your body blocked.
Because light travels in straight lines, you can predict a shadow before you make it. Imagine straight lines running from the light, past the edges of the object, onto the wall or ground — the dark zone between those lines is where the shadow lands. A common mix-up is thinking a shadow is dark stuff that comes out of you. A shadow is not stuff at all; it is a place where light is missing, like a hole in the brightness. That is also why a shadow can grow, shrink, or vanish the moment the light changes.
Worked example
A flashlight sits on a table, shining at a wall. You stand a toy dinosaur close to the wall, and its shadow is about as tall as the toy. Then you slide the toy close to the flashlight instead. What happens to the shadow, and why?
- Start with the toy near the wall and look: the shadow is sharp and about the same size as the dinosaur, because the blocked light has almost no room to spread before reaching the wall.
- Remember how light moves: it leaves the flashlight in straight lines that spread farther apart as they travel toward the wall.
- Slide the dinosaur close to the flashlight and look again: now the shadow is huge — around three times as tall as the toy — with fuzzier edges.
- Explain it with the straight lines: near the flashlight, the toy blocks the light early, while the lines are still close together; that blocked gap keeps spreading all the way to the wall, so the dark patch arrives big.
- Check by sliding the toy slowly back toward the wall: the shadow shrinks smoothly back to about toy size, which fits the straight-line idea perfectly.
Answer. The shadow grows much bigger — near the flashlight the toy blocks the spreading light early, so the blocked patch keeps widening all the way to the wall.
Check your understanding
- Why is your outdoor shadow long in the early morning and short at lunchtime, and what is the sun doing in between?
- What would happen to your shadow if two flashlights shone at you from two different sides?
- How would you explain to a friend why a shadow has the same shape as the thing that makes it?
- Why does a clear glass of water make such a weak shadow compared with a wooden block?