Try this: Dancing candle
 |
|
Draw a circle on paper and cut it out. Cut it in half
and use the half to role a cone. |
 |
|
Attach the cone to the end of the
cardboard tube and cut off the tip. |
 |
|
Fix greaseproof paper to the other
end of the tube using an elastic band. |
 |
|
Hold the tube near a candle, but
not touching. Tap the end covered in greaseproof paper.
|
 |
|
Repeat with the greaseproof paper
near a speaker, but not touching it. Make sure that the
cone is not too close to the flame. |
Warning: This experiment uses a
candle that can cause burns or a fire. Never leave a burning
candle unattended. Younger scientists will need an adult’s help.
Also ensure that the music in this activity is not too loud, as
it can damage hearing.
You will need
• paper
• compass
• pencil
• scissors
• sticky tape
• rubber band
• cardboard tube (about 30 cm x 5 cm)
• greaseproof paper
• candle
• matches or lighter
• stereo
What to do
- Use the compass to draw a
circle that has a radius of seven centimetres.
- Cut out the circle of paper.
Then, cut the circle in half.
- Roll the semicircle into a
cone and tape it shut.
- Stick the cone to one end of
the cardboard tube with the point of the cone facing
outwards like an arrow.
- Cut off the point of the
cone, leaving a five millimetre hole in the end.
- Cover the other end of the
cardboard tube with greaseproof paper. Fasten it with a
rubber band, ensuring that the greaseproof paper is pulled
taut across the opening.
- Hold the tube horizontally in
front of the candle, with the cone a couple of centimetres
from the flame. Line it up so that the hole in the centre of
the cone is level with the centre of the flame.
- Tap your finger against the
greaseproof paper and watch the flame flicker. If you hold
the greaseproof paper close to the speaker of a stereo – but
not quite touching – the flame will flicker in time with the
music.
What’s happening?
Sound moves in waves that travel through the air. These waves
are called longitudinal waves, and they cause changes in air
pressure. If you are holding the greaseproof paper near the
speaker, pressure changes are transferred to the air inside the
tube.
An increase in pressure causes a little blast of air to leave
through the hole in the tip of the cone, which makes the flame
flicker. Then, the air pressure is lower inside the tube than
outside, so air is sucked in from outside. The air being sucked
in comes from the whole area around the hole so this flow of air
is not enough to move the flame.
