Now I am become Death the destroyer of

"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 - 1930 s, 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 1015 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 feel when 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 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 hold quarks (constituents of protons and neutrons) together. � The theoretical treatment of this carrier is described in 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-, Z 0) � The carrier W can be either positively charged (W+) or negatively charged (W-), while Z is neutral (Z 0). 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.