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Physical World

Top Concepts

Ø Physics is the branch of science that deals with nature and the natural phenomenon that occur.

Ø Physics has two domains—microscopic as well as macroscopic.

The microscopic domain contains atomic, molecular and nuclear phenomenon, whereas the macroscopic domain includes phenomena taking place at the laboratory, terrestrial and astronomical scales.

Ø Science has a great influence on technology. Some of the technological advancements which are governed by scientific concepts are given below.

Technology	Scientific concept
Sonar	Reflection of ultrasonic waves
Rocket propulsion	Newton’s laws of motion
Aeroplane	Bernoulli’s principle in fluid dynamics
Steam engine	Law of thermodynamics
Optical fibres	Total internal reflection of light

Ø The physical world is governed by four fundamental forces. The four fundamental forces in nature are 1. Gravitational force.

2.  Electromagnetic force.

3.  Strong nuclear force.

4.  Weak nuclear force.

Ø The gravitational force has the following properties:

1.    It obeys the inverse square law.

2.    It is always attractive in nature.

3.    It is a long range force and extends up to infinity.

4.    The graviton is the field particle of gravitational force.

5.    It is the weakest force operating in nature.

6.    It is a central force and hence a conservative force.

Ø The properties of electromagnetic force are as follows

1.    It obeys the inverse square law.

2.    It may be attractive or repulsive in nature.

3.    It is a long range force.

4.    The photon is the field particle of electromagnetic force.

5.    It is about 10³⁶ times stronger than the gravitational force.

6.    It is a central as well as a conservative force.

Ø The nuclear force has the following properties:

1.    The strong nuclear force binds protons and neutrons in a nucleus. The weak nuclear force appears only in certain nuclear processes such as beta decay.

2.    A strong nuclear force is the strongest force in nature. It is about 100 times stronger than the electromagnetic force. Weak nuclear force is stronger than the gravitational force but weaker than the electromagnetic or strong nuclear force.

3.    It is a short-range force and is operative only over the size of nucleus.

4.    A strong nuclear force is responsible for the stability of nuclei.

Name of force	Relative strength (w.r.t. strong nuclear force)	Range	Operates among
Gravitational	10−39	Infinite	All objects in universe
Weak nuclear	10−13	Sub-nuclear size ( 10−16 m)	Electron and neutrino
Electromagnetic	10−2	Infinite	Charged particles
Strong nuclear	1	Nuclear size (10−15 m)	Nucleons and heavier elementary particles

Ø In any physical phenomenon governed by different forces, several quantities change with time, while several quantities remain constant. Such quantities are called conserved quantities.

Ø Law of conservation of linear momentum: It states that if no external force acts on a system, the linear momentum of the system remains conserved.

Ø Law of conservation of energy: It states that energy can neither be created nor destroyed; however it may change from one form to another.

Law of conservation of angular momentum: It states that if no external torque acts on a system, then the total angular momentum of the system remains conserved.