________________
32
Microcosmoldgy : Atom interactions are very very fast i.e., they take about 10-22 seconds. (Weak force reactions take about 10-10 seconds).
Because of the short range, it can never appear as a force at macroscopic level and cannot be experienced in the everyday world.
2. Electromagnetic Force is encountered in everyday world and holds together the atoms and molecules. Every subatomic particle has a positive or a negative charge or it is neutral. Positively and negatively charged particles are attracted to particles with opposite charge and repelled by those with the same charge. It varies inversely as the square of the distance separating the particles. It enables atoms to join together to form molecules and it keeps electrons in orbit around nuclei. At this level, it is the fundamental glue of the universe.
It is much stronger than the gravitational force. For instance, the force between two electrons is 10-40 times bigger than the gravitational force.
3. Weak (nuclear) force is the least known of the four forces. Its existence was inferred from the time required by certain subatomic interactions. Whereas strong force interactions happen in about 10-23 seconds, weak interactions take a much longer time i.e. about 10-10 seconds. In all probabilities, this force and the electromagnetic force are different manifestations of the same force operating at distances between particles.
4. Gravitational force : The weakest of the four is the gravitational force which is universal, i.e., every particle exerts/feels it. It is essentially a long range force, i.e., it acts over large distances, whereas the other three forces are sometimes attractive and sometimes repulsive, this one is always attractive. It holds together the solar systems, galaxies, etc. On the subatomic level, its effect is so negligible that it is ignored altogether.
PARTICLE PHYSICS
The picture of atom which emerged from the study of its nuclei showed that the matter was concentrated in microscopic
