Key Scientific Laws

Why This Matters

Scientific laws aren't just formulas to memorize—they're the fundamental rules that govern everything from why planets orbit stars to why your coffee cools down. When you're tested on these concepts, you're being assessed on your ability to recognize patterns across disciplines and apply principles to novel situations. The laws covered here span mechanics, thermodynamics, gas behavior, electricity, and genetics, and understanding the "why" behind each one will help you tackle both multiple-choice questions and complex problem-solving scenarios.

Here's the key insight: these laws are interconnected. Conservation principles show up everywhere. Proportional relationships (direct and inverse) form the mathematical backbone of physics and chemistry. Don't just memorize $F = ma$ or $PV = nRT$—know what concept each law illustrates and when to apply it. That's what separates students who struggle from those who excel.

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Conservation Principles: What Cannot Be Created or Destroyed

These laws share a powerful idea: in a closed system, certain quantities remain constant. This principle appears across physics, chemistry, and biology, making it one of the most frequently tested concepts.

Law of Conservation of Energy

• Energy transforms but never disappears—kinetic becomes potential, chemical becomes thermal, but the total stays constant
• Closed systems maintain constant total energy, which is why perpetual motion machines are impossible
• Underlies virtually every scientific field, from calculating roller coaster speeds to understanding metabolism in biology

Law of Conservation of Mass

• Mass remains constant in chemical reactions—what goes in must come out, just rearranged
• Reactant mass equals product mass, the foundation for balancing chemical equations
• Essential for stoichiometry calculations, where you'll use this to predict yields and limiting reagents

First Law of Thermodynamics

• Energy version of conservation applied to heat and work—$\Delta U = Q - W$ describes energy flow in systems
• Heat added to a system either increases internal energy or does work, never just vanishes
• Connects to engine efficiency and biological energy transfer, appearing in both physics and biology exams

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Motion and Forces: How Objects Move and Interact

Newton's framework explains why objects accelerate, stop, or change direction. These laws describe the relationship between force, mass, and motion—concepts tested heavily in mechanics.

Newton's Laws of Motion

• First Law (Inertia): Objects resist changes to their motion—no net force means no acceleration
• Second Law: $F = ma$ quantifies how force produces acceleration, inversely proportional to mass
• Third Law: Forces come in pairs—when you push a wall, it pushes back with equal magnitude but opposite direction

Law of Gravitation

• Every mass attracts every other mass with force $F = G\frac{m_1 m_2}{r^2}$, an inverse-square relationship
• Explains orbital mechanics—why planets follow elliptical paths and moons stay in orbit
• Bridges classical and modern physics, forming the foundation Newton built and Einstein refined

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Gas Behavior: Pressure, Volume, and Temperature Relationships

Gas laws describe how gases respond to changing conditions. The key is recognizing which variables are held constant and whether the relationship is direct or inverse.

Boyle's Law

• Pressure and volume are inversely proportional when temperature is constant: $P_1V_1 = P_2V_2$
• Compress a gas, pressure increases—think of a syringe or diving deeper underwater
• Foundation for understanding respiratory mechanics and industrial gas compression

Charles's Law

• Volume and temperature are directly proportional at constant pressure: $\frac{V_1}{T_1} = \frac{V_2}{T_2}$
• Temperature must be in Kelvin—this is a common exam trap; convert Celsius first
• Explains hot air balloons and why tires expand in summer, practical applications you might see in context questions

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Electricity and Electrochemistry: Current, Voltage, and Chemical Change

These laws govern how electricity flows through circuits and drives chemical reactions—essential for physics and chemistry alike.

Ohm's Law

• Voltage equals current times resistance: $V = IR$, the fundamental circuit equation
• Current is directly proportional to voltage and inversely proportional to resistance
• Used to analyze every basic circuit, from calculating power dissipation to designing safe electrical systems

Faraday's Laws of Electrolysis

• Mass deposited is proportional to charge passed—more electrons mean more product at the electrode
• Provides quantitative predictions for electrochemical reactions, linking electricity to chemistry
• Applied in electroplating, batteries, and metal refining, connecting theory to industrial processes

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Thermodynamic Direction: Why Processes Move Forward

The Second and Third Laws of Thermodynamics explain why certain processes happen spontaneously and what happens at extreme temperatures.

Second Law of Thermodynamics

• Entropy of an isolated system never decreases—disorder naturally increases over time
• Defines the direction of spontaneous processes, explaining why heat flows hot to cold, not reverse
• Limits engine efficiency—no heat engine can convert 100% of heat to work

Third Law of Thermodynamics

• Entropy approaches a minimum as temperature approaches absolute zero (0 K)
• Perfect crystals at 0 K have zero entropy, providing a reference point for entropy calculations
• Explains why absolute zero is unattainable—you'd need infinite steps to remove all thermal energy

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Heredity: How Traits Pass Between Generations

Mendel's laws explain the mechanism of inheritance, forming the foundation of genetics and appearing in biology exams consistently.

Mendel's Laws of Inheritance

• Law of Segregation: Each organism carries two alleles per trait; they separate during gamete formation so each gamete gets one
• Law of Independent Assortment: Alleles for different traits sort into gametes independently, assuming genes are on different chromosomes
• Predicts phenotype ratios like the classic 3:1 and 9:3:3:1 ratios in monohybrid and dihybrid crosses

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Quick Reference Table

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Self-Check Questions

1. Which two laws both describe conservation principles but apply to different contexts—one to mechanical/general systems and one specifically to heat and work?

2. A gas is compressed at constant temperature. Which law applies, and is the pressure-volume relationship direct or inverse?

3. Compare Newton's Second Law and the Law of Gravitation: How would you use both together to calculate the acceleration of a falling object near Earth's surface?

4. Why does the Second Law of Thermodynamics make a 100% efficient heat engine impossible? What quantity always increases?

5. In a dihybrid cross, which of Mendel's laws explains why you can treat each trait's inheritance separately, and what condition must be true for this law to apply?