ScienceGrade 3ages 8–9
🔦 Light in a straight line
A child may think a mirror "makes" light because a dark room suddenly looks bright when a mirror catches a beam, or assume light can curve around a wall the way sound seems to — but light travels in straight lines and a mirror only bounces light that's already there.
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Download on the App StoreWhat your child learns
- Light leaves and travels in straight lines.
- Something opaque, like cardboard, blocks the light.
- Behind the blocker it gets darker.
- A mirror bounces light that already arrived. It does not switch on new light.
The mistake most kids make here
A mirror makes new light, and light can snake around a wall.
Try one question
A mirror…
The mirror
- makes new light like a sun
- bounces light that is already there
- eats light forever
Answer
bounces light that is already there — Yes. A mirror bounces light that already arrived. It does not stop it.
How Maya teaches it
Your child tells Maya what they did in class. She teaches this topic at her desk, asks questions with tappable answers, and when the answer is wrong she explains why that answer was tempting instead of saying “try again”. She remembers what did not land and comes back to it.
Your child has it when they can: Say how light travels, what blocks it, and what a mirror does.
How to help at home
A mirror reflecting a bright beam into a dim corner really does look like it's "making" light appear where there wasn't any, which is a fair thing for a child to notice — the missing piece is that the light was already traveling somewhere else, and the mirror just redirected it.
Tonight, in a dim room, shine a flashlight at a wall so the beam doesn't reach a corner, then hold a small mirror to redirect that same beam into the corner. Ask your child: did the flashlight turn on again, or did the same light just go somewhere new? It's the same light, redirected.
When she says the mirror "made light," ask: "if we turned the flashlight off, would the mirror still show anything?" It wouldn't — which proves the mirror needs light to already exist before it can bounce it anywhere.
A good sign she has it: she can explain that a mirror in a dark room, with no light source at all, shows nothing — because a mirror only redirects existing light, it doesn't produce its own.
Questions parents ask
- Why does my child think a mirror creates light?
- Because a mirror can make a dim area suddenly look bright by redirecting a beam there, which looks like new light appearing. In fact, the mirror is just bouncing existing light in a new direction — it produces none of its own.
- Can light bend around a corner like sound does?
- No, light travels in straight lines and gets blocked by anything opaque in its path — that's why you get a sharp-edged shadow. Sound can bend around obstacles more easily, which is part of why the two often get confused.
- How do I show my child that light travels in a straight line?
- Shine a flashlight at an object like a book standing upright and look at the shadow behind it. The sharp edge of the shadow shows exactly where the straight-line light was blocked — a curved or fuzzy shadow would suggest bending, which doesn't happen with light this way.
- How does Maya teach this differently from a diagram of light rays?
- Maya asks what would happen to the mirror's reflection if the original light source were removed, so the child reasons through cause and effect instead of memorizing that "mirrors reflect light."
No card needed. The first lesson is free.
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Sources: Next Generation Science Standards