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Physics

Thales of Miletus

In nature, there is a force even stronger than gravity: the electrical force. Although this may seem surprising at first, it is a well-established and real phenomenon. The earliest recorded observation of this force dates back to around 600 B.C., when the ancient Greek philosopher Thales of Miletus noticed that amber, when rubbed, had the ability to attract small objects like leaves. This attraction, however, is not limited to amber; it is, in fact, a fundamental property of all matter. The word “electric” itself originates from the Greek term “ēlektron,” which means amber, underscoring the long-standing connection between this material and the discovery of electrical phenomena. Over time, it became clear that this force plays a crucial role in the interactions between particles, far surpassing gravity in strength at the atomic level.

Benjamin Frenklin

Everyday experiences demonstrate the electrical properties of matter, and Benjamin Franklin played a key role in explaining these phenomena. For instance, rubbing a plastic pen on wool can cause it to attract small pieces of paper, a sign that the object has become electrified, or electrically charged. Franklin was the first to recognize that electrified objects interact in predictable ways: an electrified piece of amber repels another electrified amber object but attracts an electrified glass rod. Similarly, when a glass rod is rubbed with silk, it repels other charged glass rods but attracts charged amber. These observations led Franklin to an important conclusion. In a simple experiment, if you rub a plastic rod on wool and suspend it with a thread, bringing another similarly rubbed plastic rod close to it will result in the two rods repelling each other. However, if you bring a rubbed glass rod near the rubbed plastic rod, they attract each other. Franklin understood that rubbing these materials caused them to become charged and that the charge on plastic was different from that on glass. He proposed that all charged objects fall into one of two categories: they either behave like plastic or like glass. Objects with the same charge repel each other, while those with opposite charges attract. Franklin gave these two categories of charge their conventional labels: negative and positive. Crucially, he chose to define the charge on glass as positive, a decision that remains the standard today. His work laid the foundation for our modern understanding of electrical charge and its behavior.

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The atom

At the start of the 20th century, research revealed that matter consists of atoms. The nucleus, located at the core, houses neutrons, which carry no electric charge, as well as protons, which possess a positive charge. Surrounding the nucleus are electron clouds, known as orbitals, that exhibit varying energy levels. Each proton and electron consistently has an identical charge of "e," though their signs are opposite. Because atoms have an equal number of protons and electrons, they remain electrically neutral.

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Different materials, like plastic and iron, react differently to electrification. When you rub a plastic rod, only the area close to the friction becomes charged, because in plastics, electrons are bound to atoms and cannot move freely. In contrast, rubbing one end of a metal rod causes the entire rod to become charged, as metals have free-moving electrons that distribute the charge across the whole object. - Metals: Free electrons allow charge to spread over the whole surface. - Non-metals (plastic, glass, wood): Electrons are bound, so only the rubbed area gets charged. Metals are conductors, while materials like plastic, glass, and wood are insulators.

Electrical insulators and conductors

When a positively charged object, such as a rod, touches an uncharged metal object, a transfer of charge takes place. Free electrons in the neutral metal are drawn to the positive charges of the charged object, causing some electrons to move from the metal to the rod. Once the objects are separated, the metal is left with a net positive charge due to the loss of electrons. This process is known as charging by contact. In a related phenomenon, when a negatively charged rod is brought near a neutral metal sphere, without touching it, the negative charges in the rod repel the free electrons in the sphere. These electrons move to the side of the sphere farthest from the rod, leaving the side closest to the rod with a positive charge. This redistribution of charges without direct contact is called charging by induction. Charging by rubbing, also known as charging by friction, occurs when two different materials are rubbed together, causing a transfer of electrons between them. One material gains electrons and becomes negatively charged, while the other loses electrons and becomes positively charged. For example, when you rub a plastic rod with a wool cloth, electrons move from the wool to the plastic rod. As a result, the plastic rod becomes negatively charged (because it gains electrons), and the wool becomes positively charged (because it loses electrons). This process creates opposite charges on both objects, which can then attract or repel other charged objects depending on the nature of their charges.

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coulomb's Law (Electric Force): Fi = hi, 9192 Where: . F. is the electric force between two charges, • kie is Coulomb's constant (8.99 x 10° Nm /C%, • 91 and 42 are the magnitudes of the charges, • r is the distance between the charges. Newton's Law of Universal Gravitation: F, = G mim, Where: . F, is the gravitational force between two masses, • G is the gravitational constant (6.674 x 10-" Nm? /kg"), • mi and mz are the masses, • r is the distance between the masses

Coulomb’s Law

Coulomb’s Law states that the electrostatic force ( F ) between two charged particles is directly proportional to the product of the magnitudes of their charges and inversely proportional to the square of the distance ( r ) between them. Coulomb’s Law and Newton’s Law of Universal Gravitation describe forces between two bodies, but they apply to different types of forces and have key differences in their nature: Type of Force: Coulomb’s Law: Describes the electrostatic force between two charged particles. Newton’s Law of Gravitation: Describes the gravitational force between two masses. Magnitude of the Forces Coulomb’s Law: Electrostatic forces can be much stronger than gravitational forces, especially at smaller distances, because the electrostatic constant is much larger than the gravitational constant . Newton’s Law of Gravitation: Gravitational forces are generally weaker compared to electrostatic forces for objects of similar size, but they dominate on large astronomical scales due to the large masses involved.

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