Physics
Gravitational and Electric Forces
Gravitational and electric forces are fundamental interactions in nature. Gravitational force is the attractive force between objects with mass, while electric force is the attraction or repulsion between charged particles. Both forces follow an inverse square law, meaning their strength decreases with distance. Gravitational force is always attractive, while electric force can be either attractive or repulsive.
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11 Key excerpts on "Gravitational and Electric Forces"
eBook - PDF- Daniel Kleppner, Robert Kolenkow(Authors)
- 2013(Publication Date)
- Cambridge University Press(Publisher)
In another great synthesis, the weak interaction and the electromagnetic interaction were unified in the 1970’s by Steven Weinberg, Sheldon Glashow, and Abdus Salaam, for which they received the Nobel Prize in 1979. 3.2 The Fundamental Forces of Physics The most familiar fundamental forces are gravity and electromag-netic forces, both of which act over a long range. Their strengths de-crease only as the inverse square of the distance between particles. In spite of this similarity, they play totally di ff erent roles in nature. The 3.3 GRAVITY 83 gravitational force always attracts, whereas electrical forces can either attract or repel. However, the major di ff erence is that gravity is incred-ibly weak compared to electromagnetic interactions. For instance, the gravitational force between an electron and a proton in a hydrogen atom is smaller than the electric force by a factor of about 10 − 30 . In large sys-tems, however, electrical attraction and repulsion cancel to a high degree, and gravity alone is left. Gravitational forces therefore dominate the cos-mic scale of our universe. In contrast, the world immediately around us is dominated by electrical forces, which are far stronger than gravity on the atomic scale. Electrical forces are responsible for the structure of atoms, molecules, and more complex forms of matter, as well as the existence of light. There are two other fundamental forces: the weak and the strong in-teractions. They have such a short range that they are important only at nuclear distances, typically 10 − 15 m. These interactions are negligible even at atomic distances, 10 − 10 m. As its name implies, the strong in-teraction is very strong, much stronger than the electromagnetic force at nuclear distances. It is the “glue” that binds protons and neutrons to-gether in the atomic nucleus, but aside from this it has little e ff ect in the everyday world.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
The strong and weak forces act only at very short distances, and are responsible for the interactions between subatomic particles including nucleons and compound nuclei. The elec-tromagnetic force acts between electric charges and the gravitational force acts between masses. All other forces are based on the existence of the four fundamental interactions. For example, friction is a manifestation of the electromagnetic force acting between the atoms of two surfaces, and the Pauli Exclusion Principle, which does not allow atoms to pass through each other. The forces in springs, modeled by Hooke's law, are also the result of electromagnetic forces and the Exclusion Principle acting together to return the object to its equilibrium position. Centrifugal forces are acceleration forces which arise simply from the acceleration of rotating frames of reference. The development of fundamental theories for forces proceeded along the lines of unification of disparate ideas. For example, Isaac Newton unified the force responsible ________________________ WORLD TECHNOLOGIES ________________________ for objects falling at the surface of the Earth with the force responsible for the orbits of celestial mechanics in his universal theory of gravitation. Michael Faraday and James Clerk Maxwell demonstrated that electric and magnetic forces were unified through one consistent theory of electromagnetism. In the twentieth century, the development of quantum mechanics led to a modern understanding that the first three fundamental forces (all except gravity) are manifestations of matter (fermions) interacting by exchanging virtual particles called gauge bosons. This standard model of particle physics posits a similarity between the forces and led scientists to predict the unification of the weak and electromagnetic forces in electroweak theory subsequently confirmed by observation.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
The strong and weak forces act only at very short distances, and are responsible for the interactions between subatomic particles including nucleons and compound nuclei. The electromagnetic force acts between electric charges and the gravitational force acts between masses. All other forces are based on the existence of the four fundamental interactions. For example, friction is a manifestation of the electromagnetic force acting between the atoms of two surfaces, and the Pauli Exclusion Principle, which does not allow atoms to pass through each other. The forces in springs, modeled by Hooke's law, are also the result of electromagnetic forces and the Exclusion Principle acting together to return the object to its equilibrium position. Centrifugal forces are acceleration forces which arise simply from the acceleration of rotating frames of reference. The development of fundamental theories for forces proceeded along the lines of unification of disparate ideas. For example, Isaac Newton unified the force responsible ________________________ WORLD TECHNOLOGIES ________________________ for objects falling at the surface of the Earth with the force responsible for the orbits of celestial mechanics in his universal theory of gravitation. Michael Faraday and James Clerk Maxwell demonstrated that electric and magnetic forces were unified through one consistent theory of electromagnetism. In the twentieth century, the development of quantum mechanics led to a modern understanding that the first three fundamental forces (all except gravity) are manifestations of matter (fermions) interacting by exchanging virtual particles called gauge bosons. This standard model of particle physics posits a similarity between the forces and led scientists to predict the unification of the weak and electromagnetic forces in electroweak theory subsequently confirmed by observation.
eBook - PDF- Sam Treiman(Author)
- 2002(Publication Date)
- Princeton University Press(Publisher)
It is a noncontact force. It acts at a distance. Electric and magnetic forces similarly act at a distance. Indeed, contact in- teractions when regarded microscopically really reflect electro- magnetic action-at-a-distance between the neighboring atoms in the two objects said to be in contact. “Contact,” that is, is not to be taken too literally at the microscopic level. All the forces of nature acting between material bodies in fact act at a distance in this sense. Indeed, all the forces that are relevant for every- day science and technology, beyond the nuclear and subnuclear C L A S S I C A L B A C K G R O U N D 29 domain and beneath the cosmic, have already been mentioned: gravity and electromagnetism! Gravity Let us start with gravity. Gravitation is attractive. The force act- ing on either one of a pair of gravitationally interacting objects points in a direction toward the other object. The magnitude of the force between any two small bits of matter is proportional to the product of their masses and inversely proportional to the square of the distance between the bits. If the masses are m 1 and m 2 and the separation distance is r , the radial force acting along the line between the masses is F = -Gm 1 m 2 /r 2 ; (2.2) where G is an empirical proportionality constant. The minus sign is put in to represent the fact that the force is attractive. This gravitational force law, which we owe to Newton, is ex- pressed here in a basic form that refers to bits of matter whose dimensions are so small compared to the separation distance r that they can be regarded as geometric points. The force acting between any two bodies A and B of finite size can be obtained from this by regarding each body as made up of many small bits and adding up (vectorially!) the forces that act between ev- ery bit in A and every bit in B. The gravitational force is very weak. It acts, for example, be- tween two books sitting on a table.
eBook - PDF- David Agmon, Paul Gluck;;;(Authors)
- 2009(Publication Date)
- WSPC(Publisher)
Chapter 10 Gravitation and Central Force Problems 349 depends on the system of units. Its small value indicates that the gravitational interaction is rather weak, as compared with say the electromagnetic interaction. The electrical repulsive force between two electrons is some 10 42 times larger than their mutual gravitational force, both calculated at the same distance. As an example, let us take m x - m 2 = 1000 kg and r = 1 m. Substituting, we find F 12 (r) = F 21 (r) = Gm 1 m 2 /r 2 =6.673-10 11 100100/l 2 =6.67310~ 7 TV. This is very small indeed, requiring extremely sensitive apparatus to detect. So for ordinary objects around us the gravitational attraction does not manifest itself. It comes into its own only for massive, celestial bodies. It is important to note that the law as formulated above for point masses is also valid for extended objects with a spherically symmetric mass distribution that depends only on the radius r. Newton was forced to invent the calculus to prove this, so that he could apply his force law to (the nearly spherically symmetric) members of the solar system. Gravity is a volume force, acting as it does on every part of a body. In a uniform gravitational field all the parts have the identical acceleration g (this has been shown experimentally to be accurate to Ag/g
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
Moreover, he refused to even offer a hypothesis as to the cause of this force on grounds that to do so was contrary to sound science. He lamented that philosophers have hitherto attempted the search of nature in vain for the source of the gravitational force, as he was convinced by many reasons that there were causes hitherto unknown that were fundamental to all the phenomena of nature. These fundamental phenomena are still under investigation and, though hypotheses abound, the definitive answer has yet to be found. And in Newton's 1713 General Scholium in the second edition of Principia : I have not yet been able to discover the cause of these properties of gravity from phenomena and I feign no hypotheses... It is enough that gravity does really exist and acts according to the laws I have explained, and that it abundantly serves to account for all the motions of celestial bodies. Einstein's solution These objections were rendered moot by Einstein's theory of general relativity, in which gravitation is an attribute of curved spacetime instead of being due to a force propagated between bodies. In Einstein's theory, masses distort spacetime in their vicinity, and other ________________________ WORLD TECHNOLOGIES ________________________ particles move in trajectories determined by the geometry of spacetime. This allowed a description of the motions of light and mass that was consistent with all available observations. In general relativity, the gravitational force is a fictitious force due to the curvature of spacetime, because the gravitational acceleration of a body in free fall is due to its world line being a geodesic of spacetime. 2. Electromagnetism Electromagnetism is one of the four fundamental interactions of nature. The other three are the strong interaction, the weak interaction and gravitation. Electromagnetism is the force that causes the interaction between electrically charged particles; the areas in which this happens are called electromagnetic fields.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
For example, a Feynman diagram can describe in succinct detail how a neutron decays into an electron, proton, and neutrino, an interaction mediated by the same gauge boson that is responsible for the weak nuclear force. Fundamental models All the forces in the universe are based on four fundamental forces. The strong and weak forces act only at very short distances, and are responsible for the interactions between subatomic particles including nucleons and compound nuclei. The electromagnetic force acts between electric charges and the gravitational force acts between masses. All other forces are based on the existence of the four fundamental interactions. For example, friction is a manifestation of the electromagnetic force acting between the atoms of two surfaces, and the Pauli Exclusion Principle, which does not allow atoms to pass through each other. The forces in springs, modeled by Hooke's law, are also the result of electromagnetic forces and the Exclusion Principle acting together to return the object to its equilibrium position. Centrifugal forces are acceleration forces which arise simply from the acceleration of rotating frames of reference. The development of fundamental theories for forces proceeded along the lines of unification of disparate ideas. For example, Isaac Newton unified the force responsible for objects falling at the surface of the Earth with the force responsible for the orbits of celestial mechanics in his universal theory of gravitation. Michael Faraday and James Clerk Maxwell demonstrated that electric and magnetic forces were unified through one consistent theory of electromagnetism. In the twentieth century, the development of quantum mechanics led to a modern understanding that the first three fundamental forces (all except gravity) are manifestations of matter (fermions) interacting by exchanging virtual particles called gauge bosons.
- Raymond Serway, John Jewett(Authors)
- 2018(Publication Date)
- Cengage Learning EMEA(Publisher)
There is physical contact between the air and the balloon. What puzzled Newton and other scientists is that gravity is a field force : There is no physical contact between a star acting as a source particle and an orbiting planet placed in the resulting field. In future chapters, we will see two other versions of the particle in a field model that turn out to be useful. In the electric version, the property of a source particle that results in an electric field is electric charge : when a second electrically- charged particle is placed in the electric field, it experiences a force. The mag- nitude of the force is the product of the electric charge and the field, in analogy with the gravitational force in Equation 5.5. In the magnetic version of the par- ticle in a field model, a charged particle is placed in a magnetic field . One other property of this particle is required for the particle to experience a force: the particle must have a velocity at some nonzero angle to the magnetic field. The electric and magnetic versions of the particle in a field model are critical to the understanding of the principles of electromagnetism, which we will study in Chapters 22–33. Because the gravitational force acting on a test particle of mass m 0 near the Earth has a magnitude GM E m 0 / r 2 (see Eq. 13.4), the gravitational field g S at a dis- tance r from the center of the Earth is g S 5 F S g m 0 5 2 GM E r 2 r ⁄ (13.8) where r ⁄ is a unit vector pointing radially outward from the Earth (see Fig. 3.15) and the negative sign indicates that the field points toward the center of the Earth as illustrated in Figure 13.4a. The field vectors at different points surrounding the Earth vary in both direction and magnitude. In a small region near the Earth’s sur- face, the downward field g S is approximately constant and uniform as indicated in Figure 13.4b. Equation 13.8 is valid at all points outside the Earth’s surface, assum- ing the Earth is spherical.
eBook - ePub- Joy Manners(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
After reading Sections 3.1 and 3.2, you may be wondering why the electrostatic force is not more apparent in everyday life. Matter has two basic properties that cause it to exert forces: one of these properties is mass, which produces gravitational forces, and the other is charge, which produces electrostatic forces. Yet, although we are aware of the gravitational force as soon as we fall out of bed in the morning, we usually have to perform an experiment before we become conscious of the electrostatic force. One of the reasons for this apparent paradox arises from the fact that there are two types of charge, positive and negative, but only one type of mass. The attraction between two equally but oppositely charged objects, and the resulting charge cancellation when they coalesce, produces a single electrically neutral body that does not exert a net electrostatic force. This explains why most lumps of matter contain precisely equal amounts of positive and negative charge and are therefore electrically neutral. However, because there is only one kind of mass, which always gives rise to an attractive gravitational force, two objects coalescing will simply form a more massive body that will exert an even greater gravitational force on other masses. As you will shortly see, the gravitational force is extraordinarily weak, but this is compensated by the very large mass of bodies such as the Earth, that exert significant gravitational forces. Although electrostatic forces are not often immediately apparent in nature, they can, under certain circumstances, produce very dramatic effects. Below we describe the conditions that give rise to two hazardous manifestations of electrostatic forces: lightning storms and the occasional explosion of oil tankers during cleaning.In 1753, a scientist called Richmann was killed during a lightning experiment. His contribution to science did not end with his death, however, for his body was dissected to discover the effects of his last experiment on his vital organs.
eBook - PDF- Joaquim A. Batlle, Ana Barjau Condomines(Authors)
- 2022(Publication Date)
- Cambridge University Press(Publisher)
On the one hand, it is one of the so-called fundamental interactions in physics: It is not the result of any underlying phenomena which combine and yield that interaction; in other words, its formulation is not phenomenological. On the other hand, it is the only interaction “at a distance” (that is, between particles separated in space without any intermediate element connecting them). All other interactions between particles that will be formulated in this section call for intermediate elements: elements connected to those particles and whose mass is significatively smaller than that of the particles. In a first approach, then, the mass of those elements can be neglected, and the force exerted by one particle at the endpoint of the element is equal, though with opposite sign, to that exerted by the other particle at the other endpoint. In other words, those two forces fulfill Newton’s 16 Particle Dynamics third law, and can be understood as an action–reaction pair of forces between the particles (Fig. 1.10). The usual intermediate elements found in mechanical systems are springs, dampers, and linear actuators. Interactions between particles through those elements are the result of underlying phenomena whose overall effect on the particles is formulated at a phenomenological level through empirical models. Gravitational Force Newton’s law of universal gravitation states that two particles P and Q attract each other with a force directly proportional to the product of their masses and inversely proportional to PQ 2 (Fig. 1.11): F grav P$Q ¼ G 0 m P m Q PQ 2 ¼ G 0 m P m Q ρ 2 : (1.11) Strictly speaking, m P and m Q in Eq. (1.11) are the gravitational masses of the particles. They are conceptually different from the inertial masses, but there is no empirical evidence so far that they should differ, so they will be treated as one same thing.
eBook - PDFElectromagnetism for Engineers
An Introductory Course
- P. Hammond(Author)
- 2013(Publication Date)
- Pergamon(Publisher)
Hence we can describe the two types of charge as positive and negative. An arbitrary choice has to be made and the charge of the proton is taken as positive. The inverse square law of force between charges is the foundation stone of electrical science. We can write it as Fe = K ^ . (2.2) 10 Electromagnetism for Engineers (10-^)^ = 5·53χ 10^'newtons (2.3) The electric force is a repulsion of F = 9 x l 0 ^ x ^ ' ' ^ ^ ' ) ' ^ Χ ΐ υ X ( 1 0 -Y = 2-30χ 10-^2 newtons (2.4) Thus the ratio of the electric to the gravitational force is /;/F^ = 4 i 7 x l 0 ^ 2 (2.5) Thus the electric force is immensely bigger than the gravitational force. Indeed, it is at first sight surprising that gravitational forces can be observed at all. The reason is that there are both positive and negative charges and that on average these cancel. Matter generally is electrically neutral, and electrical forces are balanced. In order to achieve electrical effects the electrical engineer has to separate positive and negative electric charges. Whereas electrical forces tend to cancel, gravitational forces are always attractive and additive. Thus it comes about that in spite of eqn. (2.5) motion on the earth and the motion of the heavenly bodies are controlled by gravitational and not by electric forces. 2.2 THE VERIFICATION OF THE INVERSE SQUARE LAW A reader with a sense of history will suspect the argument of the last section. If Öl and are of the same kind and thus have the same sign there is repulsion. If they have opposite signs there is attraction. The unit of charge could have been chosen as that of a proton or electron, but as we have already mentioned the SI unit has been defined by an experiment with electric currents. Since the current is measured in amperes, the unit of charge is the ampere-second and its special name is the coulomb. As we have also mentioned the forces due to the motion of charges are much smaller than those due to position.
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