What it shows
The Earth spins on its axis once a day, so one half faces the Sun and has day while the other half has night. Places further east on the globe turn into the light first, which is why the sun rises earlier in Kolkata than in Mumbai.
The science
The Sun lights only the half of the Earth that faces it. The Earth turns from west to east, completing one turn in 24 hours, so any place moves from darkness into light at sunrise, through the lit half during the day, and back into darkness at sunset. The axis is tilted by about 23.5 degrees, and keeping that tilt in the model is the first step towards explaining seasons later.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A ball or an old globe
- A knitting needle or a pencil pushed through as the axis
- A torch
- A small sticker to mark India
- A dark room
- A cardboard stand
Safety
For this project: An adult should push the needle through the ball.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Push the needle through the ball so it comes out at the two "poles" and rest it on the stand at a slight tilt.
Stick the sticker roughly where India is, a little above the middle on one side.
Darken the room and hold the torch about half a metre away, pointing at the middle of the ball.
Notice that exactly half the ball is lit; the edge of the light is the line of sunrise and sunset.
Turn the ball slowly from west to east and watch the sticker enter the light, cross the lit side and go dark.
Count how long a full turn takes and say what that represents in real life.
Put a second sticker to the east of India and show that it enters the light first.
Explain to a friend why it is night in India when it is day on the far side.
What you should see
A clear lit half and dark half on the ball, with India moving through sunrise, noon and sunset as the ball turns.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What causes day and night?
The Earth spinning on its axis.
2How long does one spin take?
About 24 hours.
3Which way does the Earth turn?
From west to east.
4Why does the Sun rise earlier in eastern India?
Eastern places turn into the sunlight before western places.
Take it further
Keep the axis tilted, walk the globe round the torch and watch which pole stays lit to introduce seasons.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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