On a moonlit night a group of differing
ages has gathered to see science in action.
The candle hidden behind the
glass jar at the center of the table
illuminates their faces and highlights
their different reactions: from anxiety
and horror to interested entertainment.
The demonstration in Joseph Wright 'of Derby's
'An Experiment on the Bird in the Air Pump'
will show the effects of
creating a vacuum and also the necessity
of air for all living creatures to survive.
The glass vessel, which holds the bird,
is connected to the air pump.
As the handle is turned and the air removed,
the bird is struggling to breathe.
Looking out at us, the scientist, or natural philosopher
as he would then have been known, has one
hand on the valve which will let the air return.
If he turns it in time the bird
may well survive but it will be changed.
Our colleagues at the Science Museum
helped us to investigate the science in
more detail.
Hi, I am Akvile from the Science Museum in London.
Today I hope for an activity that
will help you gain a better
understanding of the science behind the painting
and what's happening to the bird.
The demonstration I have is called
'No Pressure' which is also our learning
resource that is available on our
website together with many other learning resources.
So what we will need today for this demonstration is the
marshmallows in a glass bottle, a drink vacuum pump
and a rubber stopper.
We are going to see what the air pump does when
we use it, what is happening to the
marshmallows when we use the air pump,
and what is happening to the marshmallows
when we let the air back in.
So, to start with, we have some
marshmallows inside this bottle.
I will put the rubber stopper on top of the
bottle and start using the air pump.
Take a look at what is happening to these marshmallows.
We can compare with another bottle
that's full with marshmallows where the
air pump was not used: as we can see, the
marshmallows have become bigger but what
happens when we take the rubber stopper off?
There we go - it shrinks back to it's normal size but why?
Let's start by looking at the science behind this demonstration.
The atmosphere stretches above our heads for a few hundred kilometers.
The weight of that air presses down on every surface.
Trapped inside these small marshmallows are tiny air pockets
The pressure inside these pockets is at atmospheric pressure
which is the same as the air outside.
By removing the air we reduce the air pressure around the marshmallows
so the pressure inside these air pockets inside
the marshmallows is now greater which causes them to puff up dramatically.
By allowing the air back inside the bottle,
the atmospheric pressure presses down on these air pockets inside the marshmallows
which causes them to shrink back to their normal size.
Now let's imagine that we did the same experiment again
but instead of marshmallows we used the bird.
What would happen to the bird?
It might expand and it might change shape.
This happens to humans too:
the weight of the atmosphere that
surrounds the earth is pushing down on
us all the time but we don't really
think about it because we have evolved to live this way.
However this changes when we go outside the atmosphere into space.
For example, the astronaut Scott Kelly by two inches while he was in space
because his spine extended. He's now back to his normal height.
Similarly, Robert Thirsk's eyeballs changed their shape
and now he has to wear glasses.
His eyesight, perhaps, is permanently changed.
So when we look at the painting, we're really not sure of the fate of this bird
but by doing this activity we can gain a better understanding
of what it might have suffered.
This learning resource and other learning resources are available
on our Science Museum website.