Greg Laden's Blog

He asks where the tree gets its mass, but his answer is to the question where does most of its mass come from. The carbon comes from the air, yes, but the hydrogen, nitrogen, and oxygen come from the ground via the roots.

That's a bit sloppy.

Also, for an American audience, he should have first checked the meaning of 'torch'. I thought he was asking if you could start a fire.

Again, sloppy.

Posted by: 6EQUJ5 | September 6, 2008 8:42 AM

In the 17th century, Jan von Helmont planted a 5 lb willow limb in a container with 200 lb soil. He covered the container to keep airborn dust out and watered with rainwater for 5 years. At the end of five years, the willow weighed 169 lb 3 oz, and the soil had lost a couple of oz. Von Helmont is called the father of biochemistry because this is recognized as the first quantitative biochemical experiment in history. We will not pay any attention to von Helmont's published recipe for spontaneous generation of mice.

Von Helmont came to the reasonable conclusion that the increased mass of the willow came from water. This is, as it turns out, not correct, and is particularly ironic in that von Helmont was the discoverer of carbon dioxide. The tree is mostly carbohydrate, cellulose, with some other carbon based compounds. The carbon comes from CO2 as does the oxygen. Water is used in photosynthesos to supply a proton (H+) to escort an electon through the process. The oxygen in the water is a waste product and is released.

On the question of how does an airplane wing generate lift, there is sort of a false argument between Bernouli and Newton. To compound the problem--I build and fly model airplanes, particularly control line precision aerobatic airplanes. These airplanes have symmetrical airfoils and fly equally well upright or inverted. How can that be?

Posted by: Jim Thomerson | September 6, 2008 1:07 PM

One can find long discussions of how airplanes fly on various model airplane forums. Bernouli is right, but not the whole story. The Bernouli effect is that air has to flow faster over the curved top surface of the wing than under the flat bottom. The faster the air flows, the lower the pressure. How then does a flat plate airfoil fly? An important factor is angle of attack, the angle between the chord line of the airfoil and the airflow. If there is a positive angle of attack molecules on the bottom run into the wing and push it up. So both Bernouli and Newton are involved. Bernouli is, of course, a special case of Newton. As one writer put it, Bernouli gets air out of the way on the top of the wing so Newton can push the wing up from the bottom. A symetrical airfoil, at 0 angle of attack, generates no lift. So, if you carefully observe an airplane with a symmetrical airfoil flying level, you will see that the nose is tipped slightly up, making enough positive angle of attack that the wing will generate just enough lift to allow the airplane to fly along level.

Posted by: Jim Thomerson | September 6, 2008 4:52 PM

Dori is right, of course. I would like for him to have gone into a little historical explaination as to how we know that. The fact that a piece of heavy wood originated from the air is not intuitively obvious.

A couple of years ago, on the Discovery Channel, there was a program on before the dinosaurs which had several foul-ups. One was a statement that photosynthesis releases oxygen out of CO2. This was thought to be true for a long time, but experiments using heavy oxygen showed that the released oxygen was from water and the oxygen from CO2 was incorporated into the photosynthetic product. I wonder how important such a misstatement is. On the one hand it compromises the veracity of the program. On the other hand, I'm sure very few watchers noticed. But, for sure, a three foot long scorpeon is not going to be able to successfully moult out in the open air.

Posted by: Jim Thomerson | September 6, 2008 7:46 PM

Should also mention that the Wright brothers understood that a propeller is no more or less than a rotating wing. I think this is also true of turbine blades. If you get into pulse jets, ram jets, rockets, etc. you will find Bernouli lurking about in intake, combustion chamber, and exhaust design.

Posted by: Jim Thomerson | September 8, 2008 1:35 PM