Demo 6 : Fun with joysticks

05-photoresistors/README.md

@@ -34,9 +34,9 @@ The water analogy from many simpler electronics tutorials lead me to use words l
 
 1. At what point downstream from that bend does the river become the ocean? Or, for our circuits, at what point does the circuit cease to be supply voltage and become ground reference voltage?
 
-At some point after the bend in the river, the river will eventually reach the ocean. The ocean and the river are made up of different types of water. The river is fresh water; the ocean is salt water. There is an interface between the two at which point the water is neither river nor ocean, it is some mix of both. You go just a little upstream from that interface, it is the freshwater river. You go a little more downstream, it is the saltwater ocean. Electrical circuits do not behave this way. For an electrical circuit, it would be more like, as soon as the topography of the bend is complete, the freshwater river immediately ceases to be detectable and it is instantly the ocean. Even if the real body of the ocean is hundreds of miles away, at the instant where the pathway leaves the topographical bend connected to the upstream freshwater source, it becomes the river. This is because, in an electrical circuit, the concept of the hundreds of miles of riverbed between the bend and the ocean are irrelevant; the only thing that matters is the potential difference between point connection points. As soon as the downstream leg of our resistor R1 becomes attached to the rest of the circuit that eventally leads (unimpeded by another components) to ground, that downstream leg of R1 **becomes ground itself**.
+At some point after the bend in the river, the river will eventually reach the ocean. The ocean and the river are made up of different types of water. The river is fresh water; the ocean is salt water. There is an interface between the two at which point the water is neither river nor ocean, it is some mix of both. You go just a little upstream from that interface, it is the freshwater river. You go a little more downstream, it is the saltwater ocean. Electrical circuits do not behave this way. For an electrical circuit, it would be more like, as soon as the topography of the bend is complete, the freshwater river immediately ceases to be detectable and it is instantly the ocean. Even if the real body of the ocean is hundreds of miles away, at the instant where the pathway leaves the topographical bend connected to the upstream freshwater source, it becomes the saltwater ocean. This is because, in an electrical circuit, the concept of the hundreds of miles of riverbed between the bend and the ocean are irrelevant; the only thing that matters is the potential difference between point connection points. As soon as the downstream leg of our resistor R1 becomes attached to the rest of the circuit that eventally leads (unimpeded by another components) to ground, that downstream leg of R1 **becomes ground itself**.
 
-The water analogy further breaks down here when we begin thinking about current. In the river analogy, even when the river meets the ocean, there is still current. The ocean is constantly moving. So the individual water molecules never stop moving. Rivers flow because of gravity; you call the difference in altitude between a river's origin and its exit to the sea as the *potential difference*. Because of the external force of gravity, the river flows down the terrain towards lower elevations, until it eventually reaches sea level. At that point, there is no longer a *potential difference* in the river's trajectory, if there were no more external forces acting on the water, it would have no more reason to flow. There would be no current. (Let us exclude for a moment the idea of all the various forces that can act upon a still body of water to induce currents in an otherwise level body of water at sea level). 
+The water analogy further breaks down here when we begin thinking about current. In the river analogy, even when the river meets the ocean, there is still current. The ocean is constantly moving. So the individual water molecules never stop moving. Rivers flow because of gravity; you may call the difference in altitude between a river's origin and its exit to the sea as the *potential difference*. Because of the external force of gravity, the river flows down the terrain towards lower elevations, until it eventually reaches sea level. At that point, there is no longer a *potential difference* in the river's trajectory, if there were no more external forces acting on the water, it would have no more reason to flow. There would be no current. (Let us exclude for a moment the idea of all the various forces that can act upon a still body of water to induce currents in an otherwise level body of water at sea level). 
 
 Circuits behave similarly to the river in the analogy, but not exactly, because they don't have the same external forces working on them in the same way. Current only flows in an electrical circuit because there is a potential difference between one end of the circuit and the other. There is a positive and a negative; a source and a return; a supply and a ground. The difference in charge between these two points is expressed as a *potential difference*, otherwise known as a *voltage*. This difference in charge between two points is what causes current to flow, like the elevation difference in the river analogy. Whenever a circuit has no potential difference - meaning that the voltage between point A and point B is essentially 0 volts - there is no current flow. The water is perfectly still. And this brings us to the second interesting question.