The Heart and the Circulatory essays

The Heart and the Circulatory essays The Heart and the Circulatory System Imagine that you are living in the year 1535, and that you don't feel well. You have had some problems with fatigue, feeling a little more tired than usual when you walked to the market and back. You tell this to your physician, and he sends you to another physician down the street, telling you there may be some problem with your circulation. When you get to the new physician, he tells you to take off your shirt and lie down on the bench. After a quick look in your mouth, he says your vital blood is probably O.K. But he's concerned that maybe your nutritive blood is not being made fast enough. Then he starts to feel around on your abdomen. He mentions that your liver is slightly enlarged and suggests that maybe you have not been eating enough green leafy vegetables or protein. Wait a minute! You have come in with problems with your circulation, and this guy is talking about your liver and the type of foods you have been eating! What is going on here? Where did this fellow learn to p ractice medicine anyway? Confusion over the nature of the heart, the blood, and the role of the blood in the body had existed for centuries. Pliny the Elder, a Roman writer who lived from AD 23-79, and author of a 37-volume treatise entitled Natural History, wrote "The arteries have no sensation, for they even are without blood, nor do they all contain the breath of life; and when they are cut only the part of the body concerned is paralyzed...the veins spread underneath the whole skin, finally ending in very thin threads, and they narrow down into such an extremely minute size that the blood cannot pass through them nor can anything else but the moisture passing out from the blood in innumerable small drops which is called sweat." A century later Galen, a Greek physician who lived in the second century AD., spent his lifetime in observation of the human body and its functioning. Galen believed and taught his stud...

Voltage Definition in Physics

Voltage Definition in Physics Voltage is a representation of the electric potential energy per unit charge. If a unit of electrical charge were placed in a location, the voltage indicates the potential energy of it at that point. In other words, it is a measurement of the energy contained within an electric field, or an electric circuit, at a given point. It is equal to the work that would have to be done per unit charge against the electric field to move the charge from one point to another. Voltage is a scalar quantity; it does not have direction. Ohms Law says voltage equals current times resistance. Units of Voltage The SI unit of voltage is the volt, such that 1 volt 1 joule/coulomb. It is represented by V. The volt is named after Italian physicist Alessandro Volta who invented a chemical battery. This means that one coulomb of charge will gain one joule of potential energy when it is moved between two locations where the electric potential difference is one volt. For a voltage of 12 between two locations, one coulomb of charge will gain 12 joules of potential energy. A six-volt battery has a potential for one coulomb of charge to gain six joules of potential energy between two locations. A nine-volt battery has a potential for one coulomb of charge to gain nine joules of potential energy. How Voltage Works A more concrete example of voltage from real life is a water tank with a hose extending from the bottom. Water in the tank represents stored charge. It takes work to fill the tank with water. This creates a store of water, as separating charge does in a battery. The more water in the tank, the more pressure there is and the water can exit through the hose with more energy. If there were less water in the tank, it would exit with less energy. This pressure potential is equivalent to voltage. The more water in the tank, the more pressure. The more charge stored in a battery, the more voltage. When you open the hose, the current of water then flows. The pressure in the tank determines how fast it flows out of the hose. Electrical current is measured in Amperes or Amps. The more volts you have, the more amps for the current, same as the more water pressure you have, the faster the water will flow out of the tank. However, the current is also affected by resistance. In the case of the hose, it is how wide the hose is. A wide hose allows more water to pass in less time, while a narrow hose resists the water flow. With an electrical current, there can also be resistance, measured in ohms. Ohms Law says voltage equals current times resistance. V I * R. If you have a 12-volt battery but your resistance is two ohms, your current will be six amps. If the resistance were one ohm, your current would be 12 amps.