The Clear Science staff recently read a couple of articles about researching a scientific basis for the widely-believed health benefits of cranberry juice. Cranberry juice is renowned for preventing urinary tract infections (UTIs), and there is evidence that it hinders E. coli attachment to cells in the urinary tract. Also, molecules found in cranberries can chelate or bind iron atoms. They do this because they have a lot of phenolic OH group on them. Lone pairs on the oxygens chelate positive metals (chelate means “hold like a claw”). This could remove extra iron from your system.
But these theories are not without counter-evidence. The residence time of cranberry components in your system after you drink them is low. Some argue that to make a real difference, they would have to stick around much longer, or you would have to drink a lot of juice.
We called the voltaic pile the first modern battery, because some believe that objects discovered in the 1930s (that date to the biblical era) were early batteries, called “Baghdad batteries.” These have iron rods surrounded by copper tubes, and the two metals could be separated by an electrolyte. This is the basic construction of the electrochemical cell we described earlier, with iron replacing zinc.
However, it is unknown if these objects were used this way, or for some other purpose that has not been thought of. This type of battery would have a very low potential (about 0.44 volts) and would not have a lot of power. (The voltage of the cell is the difference between the individual electrode potentials.)
By connecting zinc and copper discs separated by brine-soaked cloth, a zinc-hydrogen cell in made. Alessandro Volta studied the effect produced when metals were connected this way. One of his papers (from 1769) was called De vi attractiva ignis electrici or “On the attractive force of electric fire.” In the 1800s the concept of a battery began to be developed. By connecting several cells, stacking them, a higher voltage is produced. The word voltage comes from his name.
The Clear Science Staff got an email from a producer for National Geographic a few weeks ago, and they wanted to record us explaining how a citrus battery works. (That’s us in the video BTW.) It’s for a science/comedy show that comes out next year called Duck Quacks Don’t Echo.
You put nails made out of two different metals into some acidic fruit, like an orange. If one is zinc and one is copper, you essentially make a zinc-hydrogen cell.
The battery half-reactions are 1) zinc electrodissolution (anode):
Zn → Zn2+ + 2e-
and 2) hydrogen formation (cathode):
2H+ + 2e- → H2
The zinc electrodissolution obviously happens on the surface of the zinc nail, and releases electrons. These electrons are at a low potential and want to flow to someplace at high potential. The hydrogen formation has a higher potential, and occurs when the protons (H+) in the fruit acid meet the electrons at the copper nail to form hydrogen gas (H2).
So if the two nails are connected, electrons will want to flow from the zinc nail to the copper nail. In between these two nails you place something like a cell phone. Flowing electrons are electricity, and so when they flow through the phone charger it’s electricity to charge the phone. This is how batteries work.
The Clear Science staff has been busy with battery science lately, so we haven’t had a chance to post. Perhaps talking a bit about batteries would be a good way to fill the void.
Did you know sometimes batteries are actually made of other batteries? If you cut open a 6-volt lantern battery, as they do in this video, you will find 4 smaller batteries inside. Usually these are 4 F-cell batteries (as in the video). Sometimes it is 4 D-cell batteries. An F-cell is like a D-cell but taller.
F- and D-cell batteries each have ~1.5 V potential. So that’s how they get 6 V:
The unit circle shows you all the angles from 0° to 360°. You can also refer to angles as segments of the unit circle circumference from 0 to 2π radians. If you imagine sweeping angles around the unit circle like a radar screen, it makes a series of triangles. The hypotenuse is (depending on how you look at it) either the longest side in the triangle or the radius of the unit circle.
A sine wave is what you get if you plot the triangle’s opposite side versus the angle. Sine waves are important in science and engineering, but also in music. When you’re playing a guitar the frets are all placed where they are to make certain sine waves. Light is a sine wave. Waves are sine waves. The motions of springs are sine waves. It goes on and on!
A circle is intimately related to angles. Everyone knows as you swing from 0 degrees all the way around to 360 degrees, you make a circle. The points on our unit circle figure show angles. Up above we drew bigger and bigger angles moving around the circle.
People talk about angles several different ways. If you’ve ever noticed the DRG button on a calculator, that stands for DEGREES RADIANS GRADIANS, which are three different ways to refer to angles. Our unit circle figure shows both degrees and radians. Radians are based on the how long the curvy part of a unit circle is that the angle hits. When you run all the way around 360 degrees, the curvy part is the whole circumference or 2π times the radius. So 360 degrees is 2π radians. At 90 degrees you get a quarter of that curvy part, so 90 degrees is π/2 radians.
This is an extremely useful diagram. Angles in degrees and radians, and their cosines and sines.
This is actually the kind of stuff I should be posting. Fractals are cool, but this is helpful.
The Clear Science staff is going to take a crack at convincing everyone this figure is an essential and beautiful component of everything. And by everything we mean not only science, engineering, and math but also art, music, nature, and pretty much anything else.