Posted: Feb 26, 2012 4:11 pm
Scientific hypothesese that failed, keep failing…
Humans, considered by themselves to be the smartest of apes, are natural scientists. To be more precise, all of us (whether we like it or not) from a very early age observe the physical phenomena around us and form hypotheses about how the world works.
As a species we have evolved at the bottom of a gravitational well, immersed in fluid on a rotating planet. While this arrangement can be considered fortuitous for the evolution of life (including us), it is an unfortunate environment for the young mind that is trying to do science.
I’d like to explore the idea that many overturned hypotheses appear to result in very little reaction from society as a whole and that most people will muddle on holding to their own falsified hypotheses of how the world works.
Ask a kid, or an adult….
Why can we see the moon at night?
Where do trees get the material they are made of?
How heavy is air?
If you ask these questions to enough people, you’re bound to get answers such as; “The moon makes its own light”. “Trees are made from material in the soil” and “Air doesn’t weigh anything.”
All of these answers are the product of the (falsified) scientific hypotheses we form naturally.
In our everyday experience, the only objects that appear to light up against a field of darkness, where there is no apparent external source of light, are themselves luminous. Hence, the moon ‘makes’ its own light.
Trees are massive things made out of solid stuff. They grow out of soil that is solid stuff therefore they get their stuff from the soil.
The final answer that ‘air has no weight’ is no surprise considering that our bodies have evolved in a dense atmosphere, our bodies being big bags of pressurized fluids which counter the external pressure. Thus we don’t experience this weight of air on us.
It is the discovery that air does indeed have weight that I will discuss.
Sucking….
Imagine drinking your favourite beverage with a straw. As you ‘suck’, air is being removed from your mouth and the liquid is drawn up the straw. So, how does this happen? Well, if you said something like ‘a partial vacuum is being created in the mouth and the liquid is being pulled (‘sucked’) in then you would be in agreement with Aristotle.
This would be an example of ‘horror vacui’ in action. In brief, this was a theory put forward by Aristotle which proposes that;
“…nature abhors a vacuum, and therefore empty space would always be trying to suck in gas or liquids to avoid being empty.” [1]
This was the prevailing view amongst the learned up until the 17th century. It was then when experimenters found that this hypothesis failed to explain observations and showed ‘horror vacui’ to be wrong.
The folly of spending time ‘in the weighing of ayre’….
As late as 1664, the King of England berated his scientists for wasting their time in the ‘weighing of ayre’;
“…the King would not lay, but cried him down with words only. Gresham College he mightily laughed at, for spending time only in weighing of ayre, and doing nothing else since they sat.” [2]
By the time that the King said this, and Pepys wrote it down in his diary, it had been established through experiment that air does have weight.
The discovery that air does indeed have weight can’t be put down to the work of just one individual, so let’s begin with a brief look at the work of Isaac Beeckman (1588- 1637) [3].
Beeckman, considered by his contemporaries to be one of the finest minds of his time, in 1618 worked out;
“…the law of uniformly accelerated movement of bodies falling in vacuo by combining his law of inertia with the hypothesis that the earth discontinuously attracts falling bodies by tiny impulses. On this basis he found the correct relation between time and space traversed: the distances are as the squares of the times.” [4]
Beeckman was also a practical investigator. It was through his investigations of fluids, air, volume and temperature that he began to doubt the aristoliean model;
“In 1626 he determined the relation between pressure and volume in a measured quantity of air, and discovered that pressure increases in a degree slightly greater than the diminution of the volume. Beeckman attributed the ascent of water in a pump tube not to the “horror of a vacuum,” nor yet to the “weight” of the atmosphere, but rather to the pressure of the air.” [4]
This is a key departure from the accepted view. Beeckman had discovered that it is the pressure of the air which pushes the water up a tube, as opposed to the vacuum pulling it, in a suction pump. Beeckman didn’t go so far as to posit that it was the weight of the air which caused this pressure, that was to come later.
Suction pumps suck..
Around the time of Beekman, it was a well known fact that a suction pump could only raise water to a height of “18 Florentine yards” [5] (about 9-10 metres). This is a rather inconvenient fact if you wish to pump water out of a mine or drink from a very long straw. That this should be, spurred scientists and engineers to develop other kinds of pumps (but I shall not go into that here). Scientists struggled to fit this experimental finding with Aristotle’s model. Even Galileo got it wrong.[5]
Enter Evangelista Torricelli (1608-1647) [6] who is credited with inventing the mercury barometer whilst investigating vacuums. His description of the device being;
“We have made many glass vessels ... with tubes two cubits long. These were filled with mercury, the open end was closed with the finger, and the tubes were then inverted in a vessel where there was mercury.” [7]
Now, because mercury is a much denser liquid than water it could easily be observed that it would reach a maximum height in the column, about 760mm [8].
From this observation, Torricelli makes the claim that;
“…the force which keeps the mercury from falling is external and that the force comes from outside the tube. On the surface of the mercury which is in the bowl rests the weight of a column of fifty miles of air. [7]
He then arrives at the correct conclusion that air has weight;
“Is it a surprise that into the vessel, in which the mercury has no inclination and no repugnance, not even the slightest, to being there, it should enter and should rise in a column high enough to make equilibrium with the weight of the external air which forces it up?” [7]
Taking this result and also recognizing that the density and temperature of air are inversely proportional, Torricelli went on to come up with the first scientific explanation for wind;
“... winds are produced by differences of air temperature, and hence density, between two regions of the earth” [7]
What we know now…
We live at the bottom of ‘ocean of elementary air’ [8].
The weight of that air exerts a pressure of approximately 100 000Pa (Pascals) [9]. To put that into context, 1Pa is 1 Newton of force per metre2. A regular 1kg bag of sugar has a weight of 10N, so the weight of air on a 1m2 surface is equivalent to the weight of 10 000 bags of sugar. That’s a lot.
And yet, despite this victory for science, there will always persist the misconception that ‘air has no weight’. This is simply a consequence of evolving at the bottom of a fluid filled gravitational well.
If you encounter any kids, or adults, who are under the misapprehension that ‘air has no weight’ then I strongly urge you to demonstrate the converse. The weight of air is easily demonstrated in the following manner;
[youtube]http://www.youtube.com/watch?v=6gbwAHw-EGw[/youtube]
Enjoy!
References
[1] http://en.wikipedia.org/wiki/Horror_vacui_%28physics%29
[2] http://www.pepysdiary.com/archive/1664/02/01/
[3] http://en.wikipedia.org/wiki/Isaac_Beeckman
[4] http://www.encyclopedia.com/topic/Isaac_Beeckman.aspx
[5] http://en.wikipedia.org/wiki/Suction_pu ... acuum_pump
[6] http://en.wikipedia.org/wiki/Evangelist ... to_physics
[7] http://www.gap-system.org/~history/Biog ... celli.html
[8] http://en.wikipedia.org/wiki/Barometer# ... barometers
[9] http://en.wikipedia.org/wiki/Atmospheric_pressure
Humans, considered by themselves to be the smartest of apes, are natural scientists. To be more precise, all of us (whether we like it or not) from a very early age observe the physical phenomena around us and form hypotheses about how the world works.
As a species we have evolved at the bottom of a gravitational well, immersed in fluid on a rotating planet. While this arrangement can be considered fortuitous for the evolution of life (including us), it is an unfortunate environment for the young mind that is trying to do science.
I’d like to explore the idea that many overturned hypotheses appear to result in very little reaction from society as a whole and that most people will muddle on holding to their own falsified hypotheses of how the world works.
Ask a kid, or an adult….
Why can we see the moon at night?
Where do trees get the material they are made of?
How heavy is air?
If you ask these questions to enough people, you’re bound to get answers such as; “The moon makes its own light”. “Trees are made from material in the soil” and “Air doesn’t weigh anything.”
All of these answers are the product of the (falsified) scientific hypotheses we form naturally.
In our everyday experience, the only objects that appear to light up against a field of darkness, where there is no apparent external source of light, are themselves luminous. Hence, the moon ‘makes’ its own light.
Trees are massive things made out of solid stuff. They grow out of soil that is solid stuff therefore they get their stuff from the soil.
The final answer that ‘air has no weight’ is no surprise considering that our bodies have evolved in a dense atmosphere, our bodies being big bags of pressurized fluids which counter the external pressure. Thus we don’t experience this weight of air on us.
It is the discovery that air does indeed have weight that I will discuss.
Sucking….
Imagine drinking your favourite beverage with a straw. As you ‘suck’, air is being removed from your mouth and the liquid is drawn up the straw. So, how does this happen? Well, if you said something like ‘a partial vacuum is being created in the mouth and the liquid is being pulled (‘sucked’) in then you would be in agreement with Aristotle.
This would be an example of ‘horror vacui’ in action. In brief, this was a theory put forward by Aristotle which proposes that;
“…nature abhors a vacuum, and therefore empty space would always be trying to suck in gas or liquids to avoid being empty.” [1]
This was the prevailing view amongst the learned up until the 17th century. It was then when experimenters found that this hypothesis failed to explain observations and showed ‘horror vacui’ to be wrong.
The folly of spending time ‘in the weighing of ayre’….
As late as 1664, the King of England berated his scientists for wasting their time in the ‘weighing of ayre’;
“…the King would not lay, but cried him down with words only. Gresham College he mightily laughed at, for spending time only in weighing of ayre, and doing nothing else since they sat.” [2]
By the time that the King said this, and Pepys wrote it down in his diary, it had been established through experiment that air does have weight.
The discovery that air does indeed have weight can’t be put down to the work of just one individual, so let’s begin with a brief look at the work of Isaac Beeckman (1588- 1637) [3].
Beeckman, considered by his contemporaries to be one of the finest minds of his time, in 1618 worked out;
“…the law of uniformly accelerated movement of bodies falling in vacuo by combining his law of inertia with the hypothesis that the earth discontinuously attracts falling bodies by tiny impulses. On this basis he found the correct relation between time and space traversed: the distances are as the squares of the times.” [4]
Beeckman was also a practical investigator. It was through his investigations of fluids, air, volume and temperature that he began to doubt the aristoliean model;
“In 1626 he determined the relation between pressure and volume in a measured quantity of air, and discovered that pressure increases in a degree slightly greater than the diminution of the volume. Beeckman attributed the ascent of water in a pump tube not to the “horror of a vacuum,” nor yet to the “weight” of the atmosphere, but rather to the pressure of the air.” [4]
This is a key departure from the accepted view. Beeckman had discovered that it is the pressure of the air which pushes the water up a tube, as opposed to the vacuum pulling it, in a suction pump. Beeckman didn’t go so far as to posit that it was the weight of the air which caused this pressure, that was to come later.
Suction pumps suck..
Around the time of Beekman, it was a well known fact that a suction pump could only raise water to a height of “18 Florentine yards” [5] (about 9-10 metres). This is a rather inconvenient fact if you wish to pump water out of a mine or drink from a very long straw. That this should be, spurred scientists and engineers to develop other kinds of pumps (but I shall not go into that here). Scientists struggled to fit this experimental finding with Aristotle’s model. Even Galileo got it wrong.[5]
Enter Evangelista Torricelli (1608-1647) [6] who is credited with inventing the mercury barometer whilst investigating vacuums. His description of the device being;
“We have made many glass vessels ... with tubes two cubits long. These were filled with mercury, the open end was closed with the finger, and the tubes were then inverted in a vessel where there was mercury.” [7]
Now, because mercury is a much denser liquid than water it could easily be observed that it would reach a maximum height in the column, about 760mm [8].
From this observation, Torricelli makes the claim that;
“…the force which keeps the mercury from falling is external and that the force comes from outside the tube. On the surface of the mercury which is in the bowl rests the weight of a column of fifty miles of air. [7]
He then arrives at the correct conclusion that air has weight;
“Is it a surprise that into the vessel, in which the mercury has no inclination and no repugnance, not even the slightest, to being there, it should enter and should rise in a column high enough to make equilibrium with the weight of the external air which forces it up?” [7]
Taking this result and also recognizing that the density and temperature of air are inversely proportional, Torricelli went on to come up with the first scientific explanation for wind;
“... winds are produced by differences of air temperature, and hence density, between two regions of the earth” [7]
What we know now…
We live at the bottom of ‘ocean of elementary air’ [8].
The weight of that air exerts a pressure of approximately 100 000Pa (Pascals) [9]. To put that into context, 1Pa is 1 Newton of force per metre2. A regular 1kg bag of sugar has a weight of 10N, so the weight of air on a 1m2 surface is equivalent to the weight of 10 000 bags of sugar. That’s a lot.
And yet, despite this victory for science, there will always persist the misconception that ‘air has no weight’. This is simply a consequence of evolving at the bottom of a fluid filled gravitational well.
If you encounter any kids, or adults, who are under the misapprehension that ‘air has no weight’ then I strongly urge you to demonstrate the converse. The weight of air is easily demonstrated in the following manner;
[youtube]http://www.youtube.com/watch?v=6gbwAHw-EGw[/youtube]
Enjoy!
References
[1] http://en.wikipedia.org/wiki/Horror_vacui_%28physics%29
[2] http://www.pepysdiary.com/archive/1664/02/01/
[3] http://en.wikipedia.org/wiki/Isaac_Beeckman
[4] http://www.encyclopedia.com/topic/Isaac_Beeckman.aspx
[5] http://en.wikipedia.org/wiki/Suction_pu ... acuum_pump
[6] http://en.wikipedia.org/wiki/Evangelist ... to_physics
[7] http://www.gap-system.org/~history/Biog ... celli.html
[8] http://en.wikipedia.org/wiki/Barometer# ... barometers
[9] http://en.wikipedia.org/wiki/Atmospheric_pressure