2.2 Physical Science: Matter, Energy, Forces & Motion

Physical Science: Matter, Energy, Forces & Motion

Physical Science tests your core understanding of how matter behaves, how forces interact with objects to cause motion, and how energy changes form across physical systems.

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1. Matter & Phase Transitions

Matter is anything that has mass and takes up space (volume). All matter is composed of basic building blocks called atoms.

Four Fundamental States of Matter

1. Solid: Fixed volume and fixed shape. Molecules are tightly packed in rigid, fixed positions with minimal kinetic energy.
2. Liquid: Fixed volume but indefinite shape (takes the shape of its container). Molecules are closely spaced but free to flow past one another.
3. Gas: Indefinite volume and indefinite shape (expands to fill container completely). Molecules have high kinetic energy and move rapidly in random directions.
4. Plasma: High-energy ionized gas consisting of free electrons and positively charged ions. Found in stars, lightning bolts, and neon signs.

Phase Transitions

Phase changes are physical changes driven by variations in temperature and pressure. They do not alter the chemical identity of the substance:

          [Melting]            [Evaporation]           [Ionization]
  SOLID -------------> LIQUID ---------------> GAS --------------> PLASMA
        <-------------        <---------------     <--------------
         [Freezing]            [Condensation]         [Deionization]

• Sublimation: Phase change directly from solid to gas without passing through liquid (e.g., dry ice / solid $CO_2$).
• Deposition: Phase change directly from gas to solid (e.g., frost forming on cold glass).
• Endothermic Changes: Absorb heat energy (Melting, Evaporation, Sublimation).
• Exothermic Changes: Release heat energy (Freezing, Condensation, Deposition).

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2. Classical Mechanics: Forces & Newton's Laws of Motion

A force is a push or pull exerted on an object, measured in Newtons ($N$), where $1\text{ N} = 1\text{ kg}\cdot\text{m/s}^2$.

Newton's Three Laws of Motion

Important Force Concepts

• Gravity: Universal attractive force between masses. On Earth, gravitational acceleration ($g$) is approximately $9.8\text{ m/s}^2$ ($32\text{ ft/s}^2$).
• Weight vs. Mass: Mass is the amount of matter in an object (constant anywhere, measured in kg). Weight is the force of gravity acting on that mass ($W = mg$, measured in Newtons).
• Friction: Force that opposes relative motion between contacting surfaces. Types include static friction (prevents initial movement) and kinetic friction (opposes ongoing sliding motion).

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3. Work, Power, and Conservation of Energy

Work and Power Formulas

• Work ($W$): Done when a force moves an object across a distance in the direction of the force. $W = F \times d$ (Work is measured in Joules ($J$), where $1\text{ J} = 1\text{ N}\cdot\text{m}$)
• Power ($P$): The rate at which work is performed or energy is converted over time. $P = \frac{W}{t}$ (Power is measured in Watts ($W$), where $1\text{ Watt} = 1\text{ Joule per second}$)

Forms of Energy & Conservation

• Kinetic Energy ($KE$): Energy of motion possessed by a moving body. $KE = \frac{1}{2} m v^2$
• Gravitational Potential Energy ($PE$): Stored energy due to an object's position in a gravitational field. $PE = m g h$

Law of Conservation of Energy: Energy cannot be created or destroyed; it can only transform from one form to another. In a closed system, total mechanical energy remains constant: $E_{\text{total}} = KE + PE$.

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4. Simple Machines & Mechanical Advantage

Simple machines alter the magnitude or direction of an applied effort force to make work easier, though total work performed remains equal (excluding friction losses).

Mechanical Advantage (MA): The factor by which a machine multiplies force: $\text{MA} = \frac{\text{Output Force (Load)}}{\text{Input Force (Effort)}}$.

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5. Waves, Sound & Light

A wave is a disturbance that propagates through space, transferring energy without transferring matter.

Key Wave Parameters

• Wavelength ($\lambda$): Distance between two consecutive crests or troughs (meters).
• Frequency ($f$): Number of complete wave cycles passing a point per second, measured in Hertz ($Hz$).
• Amplitude: Height of the wave crest from rest position; corresponds to wave energy/volume.
• Wave Velocity Formula: $v = f \times \lambda$.

Sound vs. Light Comparison

Electromagnetic (EM) Spectrum

Ordered from lowest frequency / longest wavelength to highest frequency / shortest wavelength: $\text{Radio Waves} \rightarrow \text{Microwaves} \rightarrow \text{Infrared} \rightarrow \text{Visible Light} \rightarrow \text{Ultraviolet} \rightarrow \text{X-Rays} \rightarrow \text{Gamma Rays}$ (Visible light spectrum mnemonic: ROYGBIV — Red, Orange, Yellow, Green, Blue, Indigo, Violet).

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6. Thermodynamics & Heat Transfer

Thermal Energy is the total kinetic energy of microscopic particles in a substance. Heat is thermal energy transferred between systems due to a temperature gradient.

Three Mechanisms of Heat Transfer

1. Conduction: Direct transfer of heat between colliding molecules in physical contact. (Most efficient in dense solids, like a metal spoon heating in soup).
2. Convection: Thermal transfer through the mass motion of fluids (liquids or gases) caused by density differences. Warm fluid expands, becomes less dense, and rises; cooler fluid sinks.
3. Radiation: Heat transfer through electromagnetic waves (infrared radiation). Requires no physical medium and can travel across empty space (e.g., sunlight heating Earth).