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Physics Fundamentals — Forces, Energy, Motion & the Laws of Nature (Beginner-Friendly - Leejohnston - 11-13-2025
Physics Fundamentals — Forces, Energy, Motion & the Laws of Nature
Physics is the study of how the universe works.
From motion and forces to energy, electricity, waves, and the structure of matter — physics explains everything from falling apples to distant galaxies.
This thread introduces the essential ideas that all physics is built on.
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1. What Is Physics?
Physics is the science of:
• forces
• motion
• energy
• electricity
• matter
• heat
• waves
• space
It aims to understand the laws that govern the universe.
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2. Forces
A force is a push or a pull.
Measured in newtons (N).
Common forces:
• weight (gravity)
• normal contact force
• friction
• air resistance
• upthrust
• tension
• electrical/magnetic forces
Balanced forces: no acceleration
Unbalanced forces: object accelerates (speed or direction changes)
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3. Newton’s Three Laws of Motion
1st Law:
Objects stay at rest or move at constant speed unless acted on by a force.
2nd Law:
Force = mass × acceleration
F = ma
3rd Law:
Every action has an equal and opposite reaction.
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4. Energy Basics
Energy cannot be created or destroyed — only transferred.
Forms of energy:
• kinetic
• gravitational
• elastic
• chemical
• thermal
• electrical
Important equations:
Kinetic Energy:
Code:
KE = ½mv²Gravitational Potential Energy:
Code:
GPE = mghWork Done:
Code:
W = Fd-----------------------------------------------------------------------
5. Motion & Graphs
Speed: distance ÷ time
Velocity: speed with direction
Acceleration: change in velocity ÷ time
Distance–time graphs:
• straight line up = constant speed
• curve = acceleration
Velocity–time graphs:
• gradient = acceleration
• area under graph = distance
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6. Electricity Basics
Current (I): flow of charge
Voltage (V): energy per charge
Resistance ®: opposition to current
Ohm’s law:
Code:
V = IRSeries circuits:
• current same everywhere
• voltage splits
Parallel circuits:
• voltage same everywhere
• current splits
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7. Waves
Waves transfer energy without transferring matter.
Two types:
• transverse (light, water)
• longitudinal (sound)
Wave equation:
Code:
v = fλv = wave speed
f = frequency
λ = wavelength
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8. The Particle Model of Matter
All matter is made of tiny particles.
Solids:
• fixed shape
• particles vibrate
Liquids:
• fixed volume
• particles slide past each other
Gases:
• no fixed shape or volume
• particles move fast and spread out
Density:
Code:
density = mass ÷ volume-----------------------------------------------------------------------
9. Common Physics Mistakes
❌ Mixing up speed and acceleration
✔ speed = how fast, acceleration = how speed changes
❌ Forgetting units
✔ m, s, N, J, V, A
❌ Thinking heavier objects fall faster
✔ only air resistance affects falling rate
❌ Confusing mass and weight
✔ mass = kg
✔ weight = force (N)
❌ Using the wrong graph type
✔ motion = distance/velocity–time graphs
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10. Practice Questions
1. A car accelerates from 10 m/s to 25 m/s in 3 seconds. Find acceleration.
2. Calculate KE of a 6 kg object moving at 4 m/s.
3. A 1200 kg car experiences a 3000 N force. Find acceleration.
4. Use v = fλ: wave speed 20 m/s, frequency 5 Hz → find wavelength.
5. A circuit has V = 12 V and I = 3 A. Find resistance.
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Summary
This beginner physics guide covered:
• forces
• motion
• Newton’s laws
• energy
• electricity
• waves
• matter
• key formulas
Mastering these ideas is the first step toward understanding the universe itself.