GRADE 9 – PHYSICS TEXTBOOK QUICKNOTES
About Lesson

This chapter introduces physics as a science, explaining its nature, scope, and significance in human society. It covers the major branches of physics, their interconnections with related fields, and highlights historical contributions that shaped modern physics.

  • Science is a systematized knowledge arising from observation, study, and experimentation.
  • Physics is the branch of natural science which describes the basic mechanisms that make our universe behave the way it does.
  • Physics is the study of everyday phenomena.
  • A person who studies physics is called a physicist.
  • Physics has several branches. Here are a couple exemples:
    • Mechanics: The study of motion, forces, and energy. Mechanics is essential for building safe roads, bridges, and houses, such as the construction of the Grand Ethiopian Renaissance Dam.
    • Acoustics: The study of sound and its properties. Acoustics is used in designing musical instruments like the krar and masenqo and improving sound quality in cultural performances.
    • Optics: The study of light and its interactions. Optics plays a role in eyeglasses, solar panels for electricity in rural areas, and improving microscopes used in hospitals.
    • Thermodynamics: The study of heat, energy, and their transformations. Thermodynamics helps in cooking more efficiently using biogas or understanding how traditional stoves can conserve energy.
    • Electromagnetism: The study of electric and magnetic fields. It powers electricity distribution in homes and supports mobile phone networks, which are crucial for communication in Ethiopia.
    • Nuclear Physics: The study of atomic nuclei and their interactions. Nuclear physics contributes to medical imaging techniques like X-rays, used in hospitals to diagnose illnesses.
    • Astrophysics: The study of celestial bodies and the universe. Astrophysics inspires space research, such as Ethiopia’s ETRSS-1 satellite, which helps monitor weather and agriculture.
  • Physics is the foundation of many important scientific disciplines such as chemistry, engineering, geology, biophysics, geophysics, medical physics, etc.
  • There are several well-known scientists and engineers that have contributed a lot to the advancement of physics:
    • Isaac Newton: Laid the foundations of classical physics and mechanics. He formulated the three laws of motion, known as Newton’s laws, and demonstrated how universal gravitation explains the motion of falling bodies and celestial objects.
    • Michael Faraday: Pioneered the field of electromagnetism. He produced mechanical motion using a magnet and electric current, later inventing the world’s first electric generator, revolutionizing how we harness energy.
    • James Prescott Joule: Discovered the relationship between heat and mechanical work, leading to the law of conservation of energy. His work laid the foundation for the first law of thermodynamics.
    • Marie Curie: Conducted groundbreaking research in nuclear physics, discovering radioactivity and elements like polonium and radium. She is often referred to as the mother of modern nuclear physics.
    • Albert Einstein: Developed the theory of relativity, transforming classical mechanics and the philosophy of physics. He also made significant contributions to quantum mechanics, establishing him as one of the greatest physicists in history.
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