Chapter 2-2 Electromagnetic Force and Magnetic Fields
The forces we can perceive in our daily lives are mainly gravity and electromagnetic force. The former is well-known as Newton's "Law of Universal Gravitation": every particle attracts every other particle in the universe with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centers. Humans can feel gravity because of the earth's gravitational pull. However, except at the poles, the gravity experienced by an object at any point on Earth is not equal to the universal gravitation. This is because universal gravitation is the earth's inherent gravitational pull, whereas gravity is the combination of an object's own mass and universal gravitation (see Figure 2.2, referencing the "Parallelogram Rule", which can be seen as the resultant force of the centripetal force produced by Earth's rotation and the gravitational force).
Figure 2.2: The Difference Between Universal Gravitation and Gravity
Clearly, gravity cannot explain why electrons orbit the nucleus to form atoms, and why various atoms interact closely to form different objects. This is actually the work of electromagnetic force. Common forces such as thrust, pull, support, elastic force, and friction all share a significant commonality: they are "contact forces" and can all be described by electromagnetic force.
Electromagnetic Force refers to the force between charged particles or charged objects. The force between two stationary charged particles is governed by Coulomb's law, which is somewhat similar to the law of gravitation. Coulomb's law states that the force of repulsion or attraction between two stationary point charges in a vacuum is proportional to the product of their charges and inversely proportional to the square of the distance between them. Electromagnetic force is much stronger than gravitational force; for example, the electromagnetic force between two adjacent protons can reach 102N, which is 1036 times the gravitational force (10-34N) between them. It is evident that, whether it is gravity or electromagnetic force, the greater the distance, the smaller the force.
Electromagnetic force is ubiquitous. Without it, we would lose all perception of the world. Human vision and hearing are based on electromagnetic force, as light and sound are fundamentally electromagnetic waves. Taste and smell are chemical sensors, and chemical reactions are fundamentally exchanges of electrons under electromagnetic force.
Touch is more closely related to intermolecular forces. From a physical standpoint, we have never actually "touched" anything. The sensation we get when we touch the skin is merely the electromagnetic force between the atoms that make up the skin, causing attraction or repulsion between the molecules of the object and the molecules of our skin, deforming the skin, and stimulating sensory neurons, ultimately forming tactile perception. Take the act of "pushing a table" as an example: both humans and tables are composed of countless molecules. On a macroscopic level, the hand pushes the table through contact. On a microscopic level, the molecules that make up the hand continuously approach the molecules that make up the table (molecules are composed of atoms, and atoms are composed of positively charged nuclei and negatively charged electrons). Thus, when these molecules and atoms approach each other, they generate electromagnetic forces, which manifest as the propulsion, tension, elasticity, friction, and other forces we perceive on a macroscopic scale.
A magnetic field is a field that transmits the physical force of magnetism between objects. It consists of moving tiny particles and exhibits particle radiation characteristics. Although it cannot be seen or touched, a magnetic field exists around magnets, and magnets can interact with each other through the magnetic field without physical contact. Objects on Earth are all composed of atoms, which generate electric currents through the movement of charges, thereby producing magnetism, making them magnets capable of "creating" or "sensing" magnetic fields.
Electromagnetic force also drives the entire Earth's engine. Thousands of kilometers beneath the earth's surface, the flow of liquid metal generates electric currents, creating a strong magnetic field that envelops the entire Earth. This process gives the earth positive and negative charges at its poles, turning it into a gigantic electromagnet. The magnetic poles of Earth's magnetic field are opposite to its geographical poles, with an angular difference known as the magnetic declination. As early as the Song Dynasty, the scientist Shen Kuo recorded in his "Dream Pool Essays"（《梦溪笔谈》）that the magnetic declination "usually deviates eastward, not all south", however, the magnetic declination is continuously changing slowly.
Early human understanding of Earth's magnetic field came from natural magnets (iron, nickel, cobalt, etc.) and the polarity of magnetic needles. The compass was one of the four great inventions of ancient China. The polarity of the magnetic needle is due to the earth's North Magnetic Pole (magnetic polarity as S pole) attracting the N pole of the magnetic needle, and the earth's South Magnetic Pole (magnetic polarity as N pole) attracting the S pole of the magnetic needle. (See Figure 2.3)
Figure 2.3: Earth's Magnetic Field
Magnetic phenomena are among the earliest recognized physical phenomena by humans. As early as 1746, British physicists demonstrated through comparative experiments that when subjected to enhanced magnetic fields (under the influence of electricity), two pomegranate trees, when compared, showed that the tree subjected to "electrical" effects grew faster and larger. Subsequently, over a span of more than 200 years, physicists and biologists tirelessly pursued "electro-culture," conducting countless scientific experiments based on precise measurements and comparisons on numerous fruits, vegetables, trees, and flowers. For more detailed comparative and historical experiments, refer to "Growing Crops and Plants by Electricity, Explaining What Has Been Done On A Practical Scale" by E.C. Dudgeon.
In China, researchers from the Chinese Academy of Sciences created an electric field using frictional electric nanogenerators to deliver electricity to plants, with experimental results published in the journal Nature.
In earlier years, scientists experimented by inserting mercury vapor lamps into various plants such as potatoes, strawberries, and sunflowers. These experiments consistently showed "significant" changes: rapid potato growth, strawberries with multiple petals, and exceptionally tall sunflowers. Later, scientists discovered through experiments that placing mercury in a circular vessel and bringing a magnet close caused the mercury inside the vessel to rotate rapidly; when placing the magnet inside the mercury vessel, the magnet itself rotated rapidly. This at least explained one possibility: mercury interacts with magnetic fields to produce stronger magnetic fields.
Regarding the use of coils around plants, it is not about directly charging the plants but rather enhancing the magnetic field around them, assuming that plants are influenced by the earth's magnetic field. This practice aims to promote cellular growth in plants (see Figure 2.4). This idea may have originated from the Tesla coil, a contemporaneous invention by Nikola Tesla, a great scientist. The Tesla coil principle involves connecting one coil to a power source as a transmitter to transmit energy and another coil to a light bulb as a receiver. When powered, the transmitter vibrates at a frequency of 10 megahertz, lighting up the bulb connected to the receiver coil, thereby achieving wireless transmission of electrical energy.
Figure 2.4：Using magnetic fields to promote plant growth
Life within the cosmos is intricately connected with nature. The human body also shares a certain intrinsic relationship with magnetic fields, which can influence the brain and organs to some extent. Not only does the human body respond to magnetic fields, but within the body itself, as part of life's processes, certain tissues and organs also generate weak magnetic fields. Over 2,300 years ago, the ancient Chinese incorporated the use of magnetic fields for disease prevention and treatment in the "Lvshi Chunqiu" （《吕氏春秋》）. Renowned physicians throughout history, such as Bian Que, Sun Simiao, Li Shizhen, and Ge Hong, documented the external or internal use of magnetite.
This reminds me of the once-popular "magnetized cups" from my childhood and the magnetotherapy products often marketed to the elderly in rural areas, such as magnetotherapy beds and pillows that supposedly cure ailments while you sleep. These are based on similar principles. While the scientific validity of these claims requires further verification, and I am not in a position to confirm their effectiveness, I offer the following reminders:
Firstly, most of these folk magnetotherapy products have not been approved by relevant authorities or undergone medical validation. Secondly, the benefits of so-called magnetotherapy may be exaggerated in marketing, offering poor value for money; consumers should be cautious to avoid financial loss. Lastly, both the earth's magnetic field and the human body's magnetic field have specific directions; therefore, it is crucial not to contradict these natural alignments.
