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"Now I am become Death, the destroyer of worlds." Robert Oppenheimer after the first test of the atomic bomb. Fundamental Forces of the atom. Elementary Particles. By the mid - 1930s, experimental evidence confirmed the existence of three sub-atomic particles.
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"Now I am become Death, the destroyer of worlds." Robert Oppenheimer after the first test of the atomic bomb. Fundamental Forces of the atom
Elementary Particles • By the mid - 1930s, experimental evidence confirmed the existence of three sub-atomic particles. • These are protons, electrons, and neutrons.
The Four Forces of Nature • The four basic forces of nature are electromagnetism, gravity, strong nuclear force, and the weak nuclear force
The Strong Force • This force is responsible for holding the nucleus together. • This force is so strong that it binds and stabilizes the protons of similar charges within a nucleus. • However, it is very short range. No such force will be felt beyond the order of 1 fm (femtometer or 10-15 m).
Electromagnetic Force • This is the force which exists between all particles which have an electric charge. • For example, electrons (negative charge) bind with nucleus of an atom, due to the presence of protons (positive charge). • The force is long range, in principle extending over infinite distance. • However, the strength can quickly diminishes due to shielding effect.
Electromagnetic Force continued • Many everyday experiences such as friction and air resistance are due to this force. • This is also the resistant force that we feelwhen pressing our palm against a wall. • This is originated from the fact that no two atoms can occupy the same space.
Electromagnetic Force 3 • its strength is about 100 times weaker within the range of 1 fm, where the strong force dominates. • But because there is no shielding within the nucleus, the force can be cumulative and can compete with the strong force. • This competition determines the stability structure of nuclei.
The Weak Force • This force is responsible for nuclear beta decay and other decay processes involving fundamental particles. • The range of this force is smaller than 1 fm and is 10-7 weaker than the strong force. • It is important in understanding the behavior of fundamental particles.
Gravitational Force • This is the force that holds us onto the Earth. • It is important in our daily life. • On the scale of the atomic world it is of negligible or no importance at all. • Gravitational force is cumulative and extended to infinity. • It exists whenever there is matter.
Gravitational Force • Your body is experiencing a gravitational pull with, say, your computer (or anything close to you or as far away as stars and galaxies) but the effect is so small you will never sense it. • However, you can sense the gravitational pull with the Earth (that is, your weight). • This is due to the cumulative effect of billions of billions of the atoms that make up your body with those atoms of the Earth.
Gravitational Force 3 • This means that the larger the body (contains more matter), the stronger the force. • But on the scale of individual particles, the force is extremely small, only in the order of 10-38 times that of the strong force.
Familiar and unfamiliar Forces • Of the 4 basic forces two of them can be experienced in our daily life. • They are also called the familiar forces which are the electromagnetic and gravitaional forces. • Similarly, the strong force and the weak force are called the unfamiliar forces.
Mystery of the Forces • How do the forces work? • Why do we sense forces - pushing and pulling? • The basic forces between particles of matter all act through a 'force carrier', which is exchanged between the interacting particles. • These exchange carriers are also known as field particles, or gauge boson
The Strong Force Carrier: Gluons (g) • Gluons have no mass and no electric charge. • They carry a special 'charge-like' property that holdquarks (constituents of protons and neutrons) together. • The theoretical treatment of this carrier is described in the theory of quantum chromodynamics (QCD)
The electromagnetic force Carrier: Photons (g) • Photons are responsible to 'carry' electromagnetic forces. • It is also known as the particle of 'light' as they also 'carry’ the light that we see. • They have no mass, and no charge and can exchange between two particles over infinite distance. • This is also the reason why light can travel to infinite distance and we can see stars that are far away. • Detailed theoretical description of photons is given in quantum electrodynamics (QED).
The weak force Carrier: W and Z (W+, W-, Z0) • The carrier W can be either positively charged (W+) or negatively charged (W-), while Z is neutral (Z0). The reason why the force is weak is because these carriers are massive, about 100 times that of the weight of a proton.
The gravitaional force Carrier: Graviton (?) • The existence of this carrier is yet to be confirmed. • If it exists it should have zero mass and zero charge. • It may will be the discovery of the century if its presence is ever detected.
Antiparticles • Particles have their antiparticles. • Antiparticles are produced in nuclear reactions when enough energy is available. • When an antiparticle and a particle meet they annihilate each other.
Fate and origin • The energy of their vanished mass along with any kinetic energy they possessed is converted to electromagnetic energy. • Antiparticles are extremely rare in nature; they are mostly produced in particle accelerators. • This picture shows the Large Hadron Accelerator located between France and Switzerland. • People use magnetic and electric fields to accelerate protons and have them collide. • These collisions result in many new subatomic particles.
