Ch 1 introduces the scope and excitement of physics — the study of nature at the most fundamental level. It covers the four fundamental forces, the nature of physical laws, and the scientific method.
Physics deals with matter, energy, and their interactions from subatomic particles to the entire universe. Classical physics: mechanics, optics, thermodynamics, electromagnetism. Modern physics: quantum mechanics, relativity, particle physics. Physics is the foundation for engineering, technology, and other sciences.
Gravitational force: between all masses, always attractive, weakest but infinite range (F = Gm₁m₂/r²). Electromagnetic force: between charges, can be attractive or repulsive, infinite range. Strong nuclear force: holds protons and neutrons in nucleus, strongest but very short range (~10⁻¹⁵ m). Weak nuclear force: responsible for beta decay, short range (~10⁻¹⁶ m). Unification: Maxwell unified electric and magnetic; electroweak theory unified electromagnetic and weak.
Download: https://ncert.nic.in/textbook/pdf/keph101.pdf | Part I: https://ncert.nic.in/textbook/pdf/keph1ps.zip
Gravitational force is the weakest force between individual particles, but it is always attractive and has infinite range. Because large objects like Earth have enormous mass, the cumulative effect is very significant. Electromagnetic forces, though stronger, usually cancel out because matter is electrically neutral overall.
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