What a shadow is
A shadow is a patch the light could not reach, because something was in the way.
Shadow A place light could not reach because something was in the way.
Step 1: Something to Notice
Watch first. The explanation comes later.
You stand in the sunshine and there is a dark shape on the ground next to your feet, the same shape as you.
What is that dark shape made of?
Step 2: Find Out
Put the solid block in the beam. Then take it away again.
Step 1 — Predict
You take the block away. What happens to the shadow?
Choose what you think will happen. You cannot see the experiment until you do — guessing first is what makes it worth watching.
Step 3: So Here Is Why
Now the explanation, after you have seen it happen.
Light goes straight
Light travels only in straight lines. It cannot bend round the back of things.
You need two things
A shadow needs a light shining and something solid standing in front of it.
Long and short
A low Sun makes long shadows, a high Sun short ones. That is why yours changes all day.
Step 4: A Common Mistake
Lots of people think
“A shadow is a dark thing that an object makes and carries around with it.”
Step 5: Why Shadows Change Size
The same idea somewhere new.
When the Sun is low in the sky your shadow is long. When it is high overhead your shadow is short. The light is coming from a different direction, so the place it cannot reach changes shape.
Step 6: Think It Through
Practice makes it stick.
The Playground
Problem 1 of 1
Your shadow is very long. Where is the Sun?
Shadows
1 of 3
Which one makes a shadow?
2 of 3
The lamp is switched off. Is there a shadow?
3 of 3
Put each picture in the right box.
Tap something to move it.
- Empty
- Empty
Step 7: Quick Check
Show what you know.
Question 1 of 1
What is a shadow?
What You Found Out
- A shadow is where light could not reach.
- Light goes in straight lines, so it cannot bend round things.
- No light means no shadow.
For the grown-up
A shadow is not a thing — A shadow is a patch where the light could not get to, because something was in the way. Nothing is put there. Something is missing there.
The shadow has the shape of the blocker — A round ball makes a round shadow. Move the ball closer to the light and the shadow gets bigger, because the ball blocks more of the spreading light.
What a shadow is — A shadow is not a thing that gets put on the ground. It is a patch the light could not reach, because something was standing in the way. Everywhere around it, light is landing. In the shadow, it is missing.
Light goes straight — Light only travels in straight lines. It cannot curve round the back of something to fill in the gap. That is the whole reason shadows exist: the ground behind the blocker is somewhere no straight line from the lamp can reach.
You need two things — For a shadow you need a light shining and something solid in front of it. Take the light away and there is no shadow — a dark room has no shadows in it at all, only dark. Take the blocker away and the light lands everywhere.
Long and short — When the Sun is low, its light comes in almost sideways, and the patch it cannot reach stretches a long way across the ground. When it is high overhead, the light comes almost straight down and the patch is a short stub under your feet. Your shadow changes all day for that one reason.