Unit 1: Physics and Human Society

Science is a collection of different scientific fields, or disciplines, whose union helps us understand the world. Physics is the most essential field of science and has a strong influence on most scientific developments. This unit explores the interconnections between physics and other sciences, its role in engineering and technology, and its specific applications in medicine, defense, and communication.

1.1 Physics and Other Sciences

Scientific disciplines do not have fixed borders; each discipline benefits from and reinforces advances in others.

Physics and Chemistry

• Overlap: Physics and chemistry overlap when systems involve matter composed of electrons and nuclei.
• Energy and Matter: Both fields are concerned with matter and its interaction with energy.
• Atomic Theory: The theory and rules about atoms important in chemistry are explained in principle by atomic and subatomic particle physics.
• Thermodynamics: The physics of heat energy tells chemists if a reaction is energetically possible and provides the composition of a system at equilibrium.

Physics and Biology

• Biomechanics: Newtonian mechanics explains how animals move, including how athletes run or how cheetahs achieve high speeds.
• Equilibrium: A body is in stable equilibrium under gravity if its center of mass is directly over its base of support.
• Fluid Dynamics: Concepts like viscosity and the equation of continuity are essential to understanding blood circulation and pressure.
• Sound production: Vocal cords produce sound when they vibrate as air passes through them during exhalation; these vibrations propagate through air molecules to reach the ear.
• Electricity: The nervous system transmits information via electrical pulses along specialized cells called neurons.
• Optics: Animals evolved light-sensitive organs (eyes) to receive information, while plants use light for photosynthesis.

Physics and Astronomy

• Astrophysics: This is the study of the physics of astronomical objects (solar systems, stars, galaxies) and the Universe as a whole.
• Gravity: Newton’s law of gravitation describes the motion of moons around planets and planets around the sun.
• Radiation: Astronomers collect electromagnetic radiation to study the birth and death of stars and the distance of far objects.
• Spectroscopy: Atomic transitions (electrons jumping between orbits) emit or absorb photons, allowing scientists to measure a star’s composition and temperature.

Physics and Geology

• Earth Science: Geology studies the solid and liquid matter of the Earth and its processes.
• Applications: Physics knowledge is used to detect useful geological deposits like ore minerals, fossil fuels, and groundwater reservoirs.

1.2 Physics and Engineering

Engineering branches are fundamentally governed by physical laws, such as mechanics, thermodynamics, and electromagnetism.

• Civil Engineering: Concerns designing and building structures like skyscrapers, roads, and dams using concepts of force, fluid pressure, and gravity.
• Mechanical Engineering: Uses physics and materials science to create mechanical systems like engines, manufacturing equipment, robotics, and vehicles.
• Electrical Engineering: Involves designing circuits, motors, electronic appliances, and communication links based on electromagnetism.
• Chemical Engineering: Relies on molecular physics and thermodynamics for the production of chemicals, plastics, and petroleum products.
• Mutual Benefit: Science uses technology to understand the natural world, while engineering uses scientific discoveries to design technology.

1.3 Medical Physics

This branch concerns the application of physics principles to medical diagnosis and treating abnormal tissues.

Imaging Technologies

• MRI (Magnetic Resonance Imaging):
  1. Uses the magnetic properties of protons (hydrogen nuclei) in body water.
  2. Protons align with a strong magnetic field and are disturbed by a pulse.
  3. When realigning, they release energy that a computer transforms into highly detailed images of soft tissue.
• X-Ray and CT Scan:
  • X-ray: Denser elements like calcium in bone block X-rays more effectively, appearing white on a shadowgram.
  • CT (Computerized Tomography): Uses a rotating X-ray source and detectors to take many successive images from different directions.

Clinical Sound

• Stethoscope: Conducts body sounds (heart, lungs) from a cavity through a tube to the examiner’s ears.+2
• Ultrasound: Uses high-frequency sound (3.5-10 MHz) to penetrate tissue; reflections are amplified to create an image on a monitor.

Therapy

• Radiation Therapy: Uses photons ($X-rays/Gamma-rays$) to destroy cancer cells by producing alterations in their biological structure.

1.4 Physics and Defense Technology

Modern defense demands knowledge of optics, sensing systems, and high-energy physics.

• Radar (RAdio Detection And Ranging):
  • Principle: Transmits signals in a direction; objects reflect an echo back to a receiver to determine range and location.
  • Range Formula: $R = \frac{ct}{2}$, where $c$ is the speed of light and $t$ is time.
• Missiles:
  • Cruise Missiles: Jet-propelled throughout flight.
  • Ballistic Missiles: Rocket-powered initially, then follow an arc trajectory governed by Newtonian mechanics.
• Infrared (IR) Night Vision: Detects heat emissions from people and objects; hotter objects appear brighter in imaging goggles.

1.5 Physics in Communication

Communication involves transferring information from a sender to a receiver through a medium.

• Wireless: Uses radio waves, microwaves, and infrared waves (e.g., satellites).
• Wired: Uses physical wires and optical fiber.
• Core Physics: Knowledge of electromagnetic theory, electrical circuits, and wave phenomena (reflection, refraction) is crucial.

Key Terminology

• Anechoic: Regions that appear black on ultrasound because they send back no sound waves (echoless).
• Astrophysics: The study of the physics of astronomical objects and the Universe as a whole.
• Ballistic missile: A missile that is rocket-powered only in the initial phase and moves under gravity and air resistance.
• Center of mass: The point at which a body is in stable equilibrium if it is directly over its base of support.
• Cruise missile: A missile that is jet-propelled throughout its entire flight.
• CT scan: An X-ray computerized tomography scan that uses a rotating source to take detailed tissue images.
• Electromagnetic Induction: The process of using changing magnetic fields to generate an electromotive force (emf).
• Geology: A branch of Earth science that studies the solid and liquid matter making up the Earth.
• Hyperechoic: Regions that appear as light gray on ultrasound because they bounce back many sound waves.
• Hypoechoic: Regions that appear dark gray because they send back fewer echoes.
• Larynx: The human voice box where vocal cords vibrate to produce sound waves.
• Medical physics: A branch of physics that applies physics principles to medical diagnosing and treating abnormal tissues.
• MRI: Magnetic Resonance Imaging, which uses proton alignment and realignment to visualize detailed soft tissue structures.
• Neurons: Specialized cells that transmit electrical pulses to carry information through the body.
• Optical fiber: A communication medium used in wired systems to transfer information.
• Pascal’s principle: Used by soft-bodied animals to produce body motion through fluid pressure.
• Physics: The most essential field of science concerned with matter and its interaction with energy.
• Radar: A system used for detecting targets and guiding weapons by radiating electromagnetic signals.
• Stethoscope: A clinical instrument used to analyze body sounds like the heart or lungs.
• Ultrasound: Sound waves with a frequency higher than 20 KHz used for medical imaging.