### Physics Class XI

Unit I: Physical World and Measurement
Chapter 1: Physical World
Unit II: Kinematics
Unit III: Laws of Motion
Chapter 5: Laws of Motion
Unit IV: Work, Energy and Power
Unit V: Motion of System of Particles and Rigid Body
Unit VI: Gravitation
Chapter 8: Gravitation
Unit VII: Properties of Bulk Matter
Unit VIII: Thermodynamics
Chapter 12: Thermodynamics
Unit IX: Behaviour of Perfect Gases and Kinetic Theory of Gases
Unit X: Oscillations and Waves
Chapter 14: Oscillations
Chapter 15: Waves

# Fundamental Forces in Nature

Force is a physical quantity which undertakes the responsibility for occurrence of most physical phenomena in the universe. There are different forces that operate in their own respective modes for outcome in an unique way. The rules operating the nature are governed by certain forces. These are known as fundamental forces in nature. They are four in number: Gravitational, Electromagnetic, Strong Nuclear and Weak Nuclear Forces.

Fundamental Forces

Gravitational Force: Any two objects in nature always attract each other. This force of attraction is developed by virtue of their masses and is called gravitational force. Gravitational force is the cause of revolution of planets around sun and every other heavenly body around larger ones.

Revolution of earth around sun causes variation in distance between them resulting in change of seasons round the year. This facilitates growth of vegetation which is the primary source of food for all food chains.

Electromagnetic Force: Two charged particles attract or repel each other depending on nature of their charge. The force acting between two charged particles is called Electrostatic force. The magnitude of this force is framed as Coulombs law which will be learnt in class XII.

Charges in motion produce magnetic field. A conductor placed in relatively varying magnetic field is called electromagnetic force. Generation of electrical energy is based on utilization of electromagnetic force to convert it into electrical energy.

Strong Nuclear Force: Atoms are considered building blocks of matter. An atom is composed of nucleus situated at center while electrons revolve around its in orbits. The nucleus is constituted of protons and neutrons. Protons are positively charged while electrons are negatively charged. Neutrons do not possess any charge and stay neutral.

In motion under external conservative force, the mechanical energy i.e., sums of kinetic and potential of energy remain constant. The concept of energy is crucial in the study of physics. The law of conservation of energy is valid across all the domain of nature. But according to Einstein’s theory, mass equivalent of energy has been related by where is the speed of light in vacuum. In a nuclear process mass is converted into energy. But conservation laws hold good in major context and play a central role in modern theories of fundamental forces in nature.