grade 9-physics_fetena_net_aabb

Physics and Human Society

Introduction
- General science includes Biology, Chemistry, and Physics.
- Unit Overview: Definition of physics, branches of physics, the relationship between physics and other fields, contributions of scientists, and the evolution of physics knowledge.
Definition and Nature of Physics
- Physics comes from the Greek word "phusis," meaning nature.
- Physics is a branch of natural science describing the fundamental aspects of the universe, including its contents, properties, and processes.
- Physics describes the basic mechanisms of how the universe behaves.
- Importance of Physics:
  - Understanding working principles of various technologies (cars, airplanes, refrigerators, etc.).
  - Explaining physical phenomena (walking on a smooth plane, electric fan rotation).
  - Discovering unknown parts of nature and understanding the modern world.
  - Understanding concepts in other subjects (Biology, Chemistry, Geology, Astronomy).
- Studying physics helps you understand concepts, relationships, principles and laws of nature.
- A person who studies physics is called a physicist.
- Career opportunities in physics:
  - Transportation
  - Aviation and space science
  - Medicine
  - Forensic and military science
  - Meteorology and metrology

Branches of Physics

With the evolution of technology, physics has expanded into many branches.
Branches of physics include:
- Mechanics: Deals with the motion of objects with or without force reference.
  - Quantum mechanics: Behavior of smallest particles (neutrons, protons, electrons).
  - Classical mechanics: Laws of motion of forces and physical objects.
- Acoustics: Study of sound, its transmission, production, and effects.
- Optics: Behavior, propagation, and properties of light.
- Thermodynamics: Study of thermal energy and heat transfer.
- Electromagnetism: Study of electromagnetic force (electric fields, magnetic fields, light).
  - Electricity
  - Magnetism
- Nuclear Physics: Structure, properties, and reactions of atomic nuclei.
- Astrophysics: Application of physics to study astronomical objects and phenomena.

Related Fields to Physics

Physics is the foundation of many scientific disciplines.
Relationships between physics and other sciences:
- Chemistry: Rooted in atomic and molecular physics, dealing with the interactions of atoms and molecules.
- Engineering: Applied in architecture for structural stability, acoustics, heating, lighting, and cooling.
- Geology: Used for radioactive dating, earthquake analysis, and heat transfer across Earth’s surface.
- Biophysics: Applies physics principles to study biological phenomena.
- Geophysics: Applies physics to study the Earth.
- Medical Physics: Diagnostics and therapy, such as X-rays and MRI, involving physics principles.

Historical Issues and Contributors

Growth of scientific knowledge has led to specialization of physics fields.
Classical physics: Physics developed from the Renaissance to the end of the 19th century.
Modern physics: Revolutionary discoveries in the 20th century transformed physics.
Laws of classical physics have been modified, resulting in changes in technology and society.
Isaac Newton: Foundations for classical physics/mechanics, formulated three laws of motion and universal gravitation.
Michael Faraday: Contributions to electromagnetism, produced mechanical motion by electric current and magnet, invented the electric generator.
James Prescott Joule: Studied the nature of heat and its relationship to mechanical work, leading to the law of conservation of energy and thermodynamics.
Marie Curie: Pioneering research in nuclear physics, discovered polonium and radium, considered the mother of modern nuclear physics.
Albert Einstein: Developed the theory of relativity and made contributions to quantum mechanics.

Physical Quantities

Introduction
- Physics begins with observation of phenomena, events, matter or energy.
  - Demanding and controlled experimentation and logical thought process.
  - The physical phenomena are described quantitatively using mathematical tools.
- Any quantitative description of a property requires comparison with a scale of different measuring devises.
- Physical quantities are classified, and conversion from one system of units to another.
Scales
- A scale on a measuring device contains the markings that show a certain amount of whatever is being measured.
- The number of marks on a measurement device depends on how accurate a measurement can be.
- As the number of marks in the measuring device increases the precision of the device increases.
Standards
- In physics, the seven basic quantities: length $(l)$ , mass $(m)$ , time $(t)$ , temperature $(T)$ , current $(I)$ , amount of substance $(n)$ , and luminous intensity $(IV )$ .
  - All other quantities in physics can be derived from these seven basic or fundamental physical quantities.
- Whatever is chosen as a standard:
  - it must be readily accessible and possesses some property that can be measured reliably.
  - measurements taken by different people in different places must yield the same result.
- International Committee revised a set of standards for length, mass, time and other basic quantities in 2019.
  - Called the SI system of units
    - Length: a distance traveled by light in vacuum during a time of $\frac{1}{299792458} s$ .
    - Time: time in SI system is second $(s)$ .
    - Mass: The kilogram $(kg)$ is defined by taking the fixed numerical value of the Plank constant $h = 6.62607015 \times 10^{-34}$ when expressed in the units of $J s$ (which is equal to $kg m^2 s$ ), where the meter and second are defined in terms of the speed of light in vacuum $(c)$ and the frequency of the Caesium 133 atom $(∆f )$ .
      $[1kg = 1.4755214\times10^{40} \frac{h∆f}{c^2}]$
Scientific Notation
- In physics, scientific notation is a way of writing measured values that are too large or too small to be conveniently written as a decimal.
 - $d \times10^n$
 - $d$ is a decimal number between 0 and 10 that is rounded off to a few decimal places
 - $n$ is known as the exponent and is an integer.
 - If n > 0 it represents how many times the decimal place in $d$ should be moved to the right.
 - If n < 0, then it represents how many times the decimal place in $d$ should be moved to the left.
Significant Figures
- each non-zero digit is a significant figure.
- Zeroes are only counted if they are between two non-zero digits or are at the end of the decimal part.
Prefixes
- When a numerical unit is either very small or very large, the units used to define its size may be modified by using a prefix.
Prefixes
- Prefix is a letter or a syllable which is written directly before a unit name with no space.
Measurement and Safety
- Measurement is the process of comparing an unknown quantity with another quantity of its kind (called the unit of measurement).
- physical quantity to be measured
- the necessary measuring tools
- units of measurements used (standard units)
  - Modern society simply could not exist without measurement.
- Every physical quantity can be represented by its numerical value and unit.
Classification of Physical Quantities
- A physical quantity is anything that you can measure.
  - Quantities that can be measured directly or indirectly are known as physical quantities.
  - The measured values of physical quantities are described in terms of number and unit
- Two types of physical quantities:
  - Fundamental or basic physical quantities
  - Derived physical quantities
- A scalar quantity is a physical quantity which has only magnitude but no direction.
  - Examples are: distance, mass, time, temperature, energy etc.
- A vector quantity is a physical quantity which has both magnitude and direction.
  - displacemen,
  - acceleration,
  - force, etc
Unit conversion
- Conversion of units is the conversion between different units of measurement for the same physical quantity, typically through multiplicative conversion factors.

Motion in a Straight Line

Motion is a continuous change in position of an object relative to the position of a fixed object called reference frame.
* A frame of reference is a set of coordinates that can be used to determine positions of objects.
* A body is said to be at rest in a frame of reference when its position in that reference frame does not change with time.
* If the position of a body changes with time in a frame of reference, the body is said to be in motion in that frame of reference.
* The concepts of rest and motion are completely relative; a body at rest in one reference frame may be in motion with respect to another reference frame.
Position
- Position is a measurement of a location, with respect to some reference point (usually an origin).
  - To describe the motion of a particle, we need to be able to describe the position of the particle and how that position changes as the particle moves.
Distance
- Distance travelled is a measure of the actual distance covered during the motion of a body
- distance is the total path length traveled by the body.
  - The distance travelled does not distinguish between motion in a positive or negative direction.
  - distance is a scalar physical quantity
Displacement
- The change of position in a certain direction is known as displacement.
 - A displacement is described by its magnitude and direction.
 - a vector quantity
 - displacement is independent of the path length taken
 - $\Delta S = Xf - Xi$
 - $\Delta S$ represents diplacement
 - $X_f$ is the final position
 - $X_i$ is the initial position
Average Speed and Instantaneous Speed
- Speed is a quantity that describes how fast a body moves.
 - the rate at which an object changes its location.
 - scalar quantity because it has a magnitude but no direction.
 - speed $\frac{distance}{time}$
 - $v = \frac{s}{t}$
 - where:
 - $v$ = velocity
 - $s$ = distance
 - $t$ = time
- Average speed is defined as the total distance travelled divided by the total time it takes to travel that distance
 - $v{av} = \frac{s{tot}}{t_{tot}}$
 - where:
 - $v_{av}$ = average velocity
 - $s_{tot}$ = total distance
 - $t_{tot}$ = total time
- The speed at any specific instant is called the instantaneous speed.
 - $v = \lim_{\Delta t \to 0} \frac{\Delta s}{\Delta t}$
Average Velocity and Instantaneous Velocity
- Velocity is a physical quantity that describes how fast a body moves as well as the direction in which it moves.
  - vector quantity
  - The SI unit of velocity is meter per second (m/s).
- The average velocity is expressed as
  - $v_{av} = \frac {\Delta X}{\Delta t} = \frac{S}{\Delta t}$
- instantaneous velocity of a body is its velocity at any time t
  - For a body that undergoes uniform motion, the velocity of the body is uniform and the average velocity and the instantaneous velocity are the same.
Acceleration
- Acceleration is the rate of change of velocity.
- Acceleration is denoted by $\vec{a}$
- SI unit is $\frac{m}{s^2}$
- If the initial velocity of a body is $\vec{vi}$ at a time $ti$ , and the final velocity is $\vec{vf}$ at a time $tf$ , the average acceleration is, from the definition,
 $\vec{a}{av}= \frac{\vec{vf} - \vec{vi}}{tf - t_i}$
Uniform Motion
- the motion of an object along a straight line with a constant velocity or speed in a given direction.
  - The acceleration is zero (a=0) because neither the magnitude of the velocity nor its direction changes.
Graphical Representation of Motion
- Position-Time Graph
- Slope = $\frac{vertical \space change}{horizontal \space change} = \frac{\Delta X}{\Delta t} = V_{av}$
- Velocity time graph

Forces, Work, Energy and Power

The Concept of Force
- a force is a push or a pull exerted on a body that changes the state of motion of the body causing a change in velocity or deformation by changing its shape or size.
  - Force is a vector quantity.
  - SI unit of force is newton represented by $N$
  - A force can always not cause motion.
- Contact Force
  - physical contact between objects
- Non-contact Forces
  - do not involve physical contact between objects
- Weight: is the magnitude of the gravitational force acting on a body
Newton’s Laws of Motion
- Newton's First law of motion (Law of Inertia)
 - a body continues to be in its state of rest or of uniform motion in a straight line unless it is acted on by unbalanced force.
 - Mass is a measure of inertia
- Newton’s second law of motion
 - the acceleration of a body is directly proportional to the net force acting on it and inversely proportional to the mass of the body.
 - $F = ma$
 - where:
 - $F$ = force
 - $m$ = mass
 - $a$ = acceleration
 - $1N = 1 \frac{kg \cdot m}{s^2}$
- Newton's third law of motion
 - every action has an equal and opposite reaction.This means that forces always act in pairs.
 - $F{12} = -F{21}$
Forces of friction
- resistance to the motion of the object from