What it shows
A comet’s tail always points away from the Sun, even when the comet is moving away. The solar wind and light push the dust and gas outwards, so the tail leads when the comet is going away.
The science
A comet is a lump of ice and dust. Near the Sun, the ice turns to gas and releases dust. The solar wind (charged particles) and sunlight push this material away from the Sun, forming one or two tails. So the tail is a stream pushed outwards, and it does not trail behind the comet.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A foam or paper ball for the nucleus
- Cotton wool or thin strips of tissue paper for the tail
- A table fan or hair-dryer on cool setting to act as the Sun
- A cardboard ring track for the orbit
- A stick and a string
- Black paper background
Safety
For this project: Use only a fan with guards, and an adult must plug in the fan. Do not use a hot dryer near paper.
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.
Draw an oval orbit on a large black sheet with the Sun at one focus using a pin and string.
Place the fan at the Sun position pointing outwards across the sheet.
Make a comet by gluing tissue strips to a ball so they can fly freely.
Hang the comet from a stick and move it along the orbit while the fan blows.
Watch the tail direction at four positions: far, approaching, near and leaving.
Draw the tail direction as an arrow on your orbit diagram at each position.
Make the tail longer at the near position by adding more tissue, showing more material released.
Write a caption that explains why the tail leads when the comet is leaving.
What you should see
A comet that swings round the oval, its tissue tail always blown away from the fan Sun, and a labelled diagram that shows the four tail positions.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is a comet made of?
Ice, dust and rock.
2Why does it grow a tail near the Sun?
Heat turns ice to gas and frees dust.
3Which way does the tail point?
Always away from the Sun.
4Name a famous periodic comet.
Halley’s comet, returning about every 76 years.
Take it further
Research why a comet has a separate curved dust tail and a straight gas tail.
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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