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 200. 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 small guarded battery or USB-powered fan (or a paper hand fan) 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 small guarded battery or USB fan and keep fingers and hair away from it; an adult must help set it up.
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.
Step 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 two pins and a loop of thread.
Place the fan at the Sun position, which will be turned at each comet position to blow outwards from the Sun.
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, turning the fan each time so that it points from the Sun position straight at the comet.
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.
01What is a comet made of?
Ice, dust and rock.
02Why does it grow a tail near the Sun?
Heat turns ice to gas and frees dust.
03Which way does the tail point?
Always away from the Sun.
04Name 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.
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