GREAT
EXPLORATIONS - Moving air | Forming
images | Reflecting light | Electricity
and magnetism | Spinning things | Making
sense | Changing colours | Making
sounds and waves | Moving to and fro
| Thinking about shapes
This is an old set of proven ideas, for reference. My latest designs are
far better!
Moving
air
Bernoulli
blower
TEXT:
Can you make
things hover in the jet of air?
Which objects do you
think work best? Can you make more than one thing hover at the same time?
Why don't things fall
off to one side? Can you see that whenever a hovering object wobbles out
near the edge of the air stream, it seems to be pushed back towards the
faster-moving air in the middle?
If you look closely at the picture, you can see a smaller ball hovering
below the larger one. This version of the ever popular blower exhibit
has the air jet surrounded by a flat table on which a varied selection
of different 'flying objects' is kept, even including plastic food-mixing
bowls. Most blower exhibits are likely to eject dropped coins etc. like
bullets, but this version has a U-shaped duct and the blower faces downwards.
Invisible
smoke rings
((Sorry, no picture)
TEXT:
Hit the soft end of the barrel
with your hand and watch what happens to the "target" screen.
You have formed a spinning ring of air, just
like a smoke ring but without any smoke. Ask a friend to volunteer to
be "shot".
The ring of air is not spinning sideways but
in a rolling, inside-out sort of way so that air at the middle of the
ring is always pushing fowards.
A green plastic drum, with a large hole at one end and a flexible diaphragm
at the other. The target screen is fitted with numerous loops of ribbon
which move when the 'toroidal vortex' hits them.
Streamlines
TEXT:
Look at the way the strings are
blowing in the wind.
Move the shapes around to find out how differently
the air is moving around each of them.
Does air flow more smoothly round a round shape
or a streamlined "fish-shape"? Does air flow more smoothly round
the "fish-shape" when you put the round end or the pointed end
at the back?
The flat surface is covered with strong, soft threads which show the
direction of air flow. The effect works extremely well. Not surprisingly,
it isn't particularly popular with unaccompanied children. For this one
they benefit from the company of an adult to focus their attention on
what is happening here.
Pressure
messenger
TEXT:
Blow the bright-coloured "messenger"
right round the building.
To do this, hold one end of the pipe over
the air jet and watch carefully.
Send it back again by connecting the other end
to the air jet. The distance travelled is about 80 metres. Can you time
the "messenger" and work out how fast it moves?
The picture does not do justice to it. I was really proud of this one.
The answer is about 40 miles per hour, by the way.
Hover
track
TEXT:
Block the end of the tube to stop
the air from blowing out.
The slider will work much more easily when
you do this.
When you block the end, can you feel the air
blowing out through the tiny holes in the long tube? Do you think the
slider is actually touching the long tube when this is happening?
Another original idea that I'm quite proud of, based on the more delicate
classroom demonstration. The slider is a short plastic tube running over
an aluminium tube with air holes along the top. The neat feature is the
way it conveys its message about friction. The slider only hovers when
you put your hand over the open end of the aluminium tube. Then it gently
drifts down the slope towards you.
GREAT
EXPLORATIONS - Moving air | Forming
images | Reflecting light | Electricity
and magnetism | Spinning things | Making
sense | Changing colours | Making
sounds and waves | Moving to and fro
| Thinking about shapes
This is an old set of proven ideas, for reference. My latest designs are
far better!
|
