Unit 1: Application of Physics in Other Fields

Physics is the foundational science that serves as the “union” of all scientific disciplines, providing the collection of fields needed to understand our world. This unit demonstrates how physical laws—from Newtonian mechanics to electromagnetism—drive innovation across all sectors of society.

1.1 Physics and Other Sciences

Scientific disciplines do not have fixed borders; they benefit from and reinforce one another.

Physics and Chemistry

• Matter Interaction: Overlaps occur when studying matter composed of electrons and nuclei.
• Atomic Theory: Principles of atomic and subatomic particle physics explain the rules of chemistry regarding atoms and molecules.
• Energy: Both fields are concerned with the interaction between matter and its interaction with energy.

Physics and Biology

• Newtonian Mechanics: Explains how athletes run and how the fastest animals, like cheetahs, achieve high speeds.
• Stable Equilibrium: A body is stable 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 vital for understanding blood circulation and pressure.
• Pascal’s Principle: Soft-bodied animals (sea anemones, earthworms) lack a firm skeleton and use this principle to produce body motion.
• Sound Waves: Vocal cords vibrate during exhalation to produce sound waves; these mechanical waves propagate and vibrate the eardrum, which the brain interprets as sound.
• Electricity: The nervous system transmits messages via electrical pulses through a network of specialized cells called neurons.
• Optical Physics: Study of light (400–700 nm) is essential for photosynthesis and understanding the light-sensitive organs (eyes) of animals.

Physics and Astronomy (Astrophysics)

• Planetary Motion: Newton’s law of gravitation and concepts of centripetal/centrifugal force describe the orbits of moons and planets.
• Light as a Ruler: Astronomers measure distance based on the apparent brightness versus true brightness of astronomical objects.
• Spectroscopy: The wavelength of emitted light (photons) from atoms reveals the chemical composition and temperature of far-off stars.

Physics and Geology

• Earth Science: Branch that studies all aspects of the Earth, including the core and atmosphere.
• Mineralogy: A specialty studying the composition and structure of minerals (e.g., quartz, magnetite).
• Geophysical Prospecting: Physics is used to detect ore minerals, fossil fuels, and geothermal reservoirs.

1.2 Physics and Engineering

Engineering uses scientific discoveries to design products and processes that solve societal problems.

• Civil Engineering: Concerns the design of skyscrapers, bridges, and dams using knowledge of forces, fluid pressure, and gravity.
• Mechanical Engineering: Applies mechanics, dynamics, thermodynamics, and aerodynamics to create engines, vehicles, and robotics.
• Electrical/Electronics Engineering: Designs circuits, motors, and fiber optic networks based on electromagnetism and semiconductor physics.
• Chemical Engineering: Uses molecular physics and thermodynamics to process raw materials into plastics, petroleum, and detergents.
• Technology Generating Physics: Technology created by science often enables “new physics.” For example, rocket technology allows for measurements in space, and X-ray technology helped develop our understanding of atomic structure.

1.3 Medical Physics

This branch applies physics principles to medical diagnosis and the treatment of abnormal tissues.

• Magnetic Resonance Imaging (MRI):
  1. Protons: The scanner uses the magnetic properties of protons (hydrogen nuclei) abundant in body water.
  2. Magnetic Alignment: Protons act as small magnets and align parallel to the scanner’s constant magnetic field.
  3. Radio Frequency Pulse: A current pulse disturbs this alignment; when turned off, protons realign and release absorbed energy.
  4. Tissue Contrast: Different tissues (gray matter, blood) release different energy levels, allowing a computer to generate a highly detailed image.
• X-Ray Computerized Tomography (CT) Scan:
  • Conventional X-ray: A stationary machine sends X-rays through the body. Denser elements like calcium (in bone) block X-rays effectively, appearing white.
  • CT Scan: Uses computers and a rotating X-ray machine to take many successive “tomograms” (images) from different directions.
• Clinical Sound:
  • Stethoscope: A bell-shaped cavity and tube used to listen to heart, lung, and blood flow sounds.
  • Ultrasound: Uses high-frequency sound (3.5–10 MHz) to penetrate tissue. Reflected waves are used to visualize the form and structure of organs.
• Radiotherapy: Uses external radiation beams to cure internal body cancers and tumors without surgery.

1.4 Physics and Defense Technology

Modern defense forces (Army, Navy, Air Force) demand advancements in sensing, optics, and high-energy physics.

• Radar (RAdio Detection And Ranging):
  • Principle: Radiates electromagnetic signals and examines the echo received from a distant object to determine range and location.
  • Formula: Range $R = \frac{ct}{2}$ (where $c$ is the speed of light and $t$ is the two-way travel time).
• Missiles:
  • Cruise Missiles: Jet-propelled throughout flight; they obtain oxygen from the air.
  • Ballistic Missiles: Rocket-powered only in the initial phase, following an arc trajectory governed by gravity and Newtonian mechanics.
• Infrared (IR) Wave Detection:
  • Night Vision: Devices detect infrared light emitted by all people and objects proportional to their temperature.
  • Imaging: Hotter objects appear brighter; green is typically used for the display as it is best for natural human night vision.

1.5 Physics in Communication

Communication is the process of transferring information from one point to another.

• Wireless Systems: Use radio waves, microwaves, and infrared waves (e.g., satellite and ground wave communication).
• Wired Systems: Use physical wires or optical fiber.
• Foundational Knowledge: Includes electromagnetic theory, electrical circuits, and wave phenomena like reflection, refraction, and interference.

Exhaustive Key Terminology List

• Anechoic: Regions that appear black on ultrasound because they send back no sound waves (fluid-filled).
• Astrophysics: The study of astronomical objects using physics principles.
• Ballistic Missile: A missile that is rocket-powered only during its initial flight phase.
• Center of Mass: The point where a body’s mass is concentrated; vital for stable equilibrium.
• Cruise Missile: A missile that is jet-propelled throughout its entire flight.
• CT Scan: Uses rotating X-ray machines to make many successive images (tomograms).
• Electromagnetic Induction: A process where changing magnetic fields produce electricity; the basis for generators.
• Geology: The study of solid and liquid matter that makes up the Earth.
• Hyperechoic: Regions that appear bright on an ultrasound image because they reflect many waves.
• Hypoechoic: Regions that appear dark gray on ultrasound because they reflect fewer waves.
• Larynx: The organ (voice box) where vocal cords vibrate to create sound waves.
• Medical Physics: Branch concerning physics applications in medical diagnosis and treatment.
• MRI: Uses magnetic resonance of protons to image internal soft tissue.
• Neurons: Specialized cells that transmit messages via electrical pulses.
• Optical Physics: The study of light and its applications (microscopes, vision, lasers).
• Pascal’s Principle: Used by soft-bodied animals to produce locomotion.
• Protons: Hydrogen nuclei used in MRI for their magnetic properties.
• Radar: An acronym for RAdio Detection And Ranging.
• Stethoscope: Tool used for clinical analysis of body sounds (heart, lungs).
• Ultrasound: Sound waves with a frequency higher than 20 kHz.