Hippocampus Physics: Charge and Matter

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You learned previously that an inherent property of an object is its mass. An object with a smaller mass has a smaller inertia compared to an object with a larger mass. Along with mass, another inherent property of an object is its electrical charge. The concept of electrical charge has been around for centuries and has its roots in a simple experiment first reported by Thales of Miletus in 600 BC. If you rub a plastic rod with fur and suspend it by a string, and then rub a second plastic rod and bring it near the suspended rod, the suspended rod will move away. However, when a rod of glass rubbed with silk is moved close to the suspended rod, the suspended plastic rod will move toward the glass. The conclusion that was made from this experiment is that two different types of electrical charges exist, and that opposite charges attract one another and like charges repel one another. Benjamin Franklin named the two different types of charges positive and negative. The basic unit of charge in the MKS system is the Coulomb, which is abbreviated by C. On an atomic level, individual particles carry charge. Protons are positively charged, and electrons are negatively charged. A third type of particle exists called the neutron; neutrons have no charge. Protons and electrons carry the same amount of charge, denoted by the letter q. This basic unit of charge has been determined to be 1.60 ´ 10-19 C. The neutron, which is neutral, has no charge. Even though protons and electrons carry an equal but opposite amount of charge, their masses are very different. The proton mass is 1.67 ´ 10-27 kg, while the electron mass is 9.11 ´ 10-31 kg. The neutron's mass is almost the same as the proton's mass. These are very small numbers, but the thing to keep in mind is that protons are almost two thousand times heavier than electrons. Atoms are made up of a nucleus of positively charged protons surrounded by negatively charged electrons.