List of Lessons | Subjects

Understanding Physics

by Ron Kurtus (updated 17 March 2023)

Physics is a branch of Physical Science that is concerned with the study of the properties of matter, its motion, and the concepts of energy and force. The subject can be divided into three main areas: Classical Physics, Relativity, and Quantum Mechanics. The material here will concentrate on classical or everyday physics.

The knowledge of Physics is important for the development of the products we use. It is also an interesting and exciting subject of value in many walks of life. There is a great need for people who understand scientific principles and know how to think logically. Your knowledge and skills in these areas can help you excel in school, advance your career or improve your business.

The purpose of these free online lessons is to give you a start at improving your scientific knowledge of physics that will help you become a champion in the field.

Physics Contents

Basics of Physics

Physics Overview

Using Mathematics in Physical Science

Fundamental Units of Measurement

Using a Scientific Calculator

Sensors and Detectors

Physics of Computer Games

Three Levels of a Champion in Science

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Overview of Study of Matter

Definition of Matter

Theories of Matter

Kinetic Theory of Matter

Measurement of Mass

Particles of Matter

Structure of the Atom

Are Atoms Tiny Solar Systems?

Atomic Weight

Fundamental Subatomic Particles





Density of Matter

Factors Affecting Density of Matter

Archimedes Solves Density Problem

States of Matter

States of Matter

Changing States of Matter

Pressure and States of Matter

Temperature Constant During Phase Change

Exotic States of Matter

Evaporation is Changing Liquid to Gas


When Water Vapor Becomes Snow

Dry Ice is Solid Carbon Dioxide

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Characteristics of Fluids

Pressure in Fluids

How Objects Float in Fluids

Applications of Fluid Principles

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Relative Motion, Speed, Velocity and Acceleration

Newton's Laws of Motion

Motion and the Law of Inertia

Periodic Motion

Periodic Motion

Pendulum Exhibits Periodic Motion

Demonstration of a Pendulum

Equations for a Simple Pendulum

Newton's Cradle

Derivation of How Newton's Cradle Works

Wave Motion

Overview of Wave Motion

Units of Frequencies and Wavelengths

Waves and Obstacles

Waveform Noise

Pulse Waves

Doppler Effect for Waveforms

Conventions for Doppler Effect Equations

Summary of Doppler Effect Equations

Derivation of Doppler Effect Wavelength Equations

Derivation of Doppler Effect Frequency Equations

Derivation of Doppler Effect Velocity Equations

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Sound Waves - Acoustics

Overview of Sound Waves

Creating Sound Waves

Frequencies and Wavelengths of Sound

Speed of Sound in a Gas

Doppler Effect for Sound

Doppler Effect Equations for Sound

Traveling Faster than Sound

Making Sounds with Musical Instruments

Sound Created from a String or Wire

Equation for Sound Created from a String

Equation for Sound Created from a Wire

Detecting Sound Waves

How Obstacles Affect Sound Waves

Sound Echoes

Sound Seems Amplified Over Water

Reproducing Sounds

Beat Frequencies in Sound

Acoustics in Buildings

Noise Reduction

Active Noise Cancellation

Hearing - Using your Senses

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Visible Light Waves - Optics

Visible Light

Speed of Light

Doppler Effect Equations for Light

Refraction of Light

Snell's Law for the Refraction of Light

Dispersion of Light

Optical Devices


Laser Battle Game (Java applet)

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Electromagnetic Waves

Electromagnetic Waves

Electromagnetic Spectrum

Infrared Radiation

Infrared, Gases and the Greenhouse Effect


X-ray Characteristics

X-ray Generation

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Electricity and Magnetism

Main Electricity and Magnetism menu page. Areas of interest are:

Electricity Basics

Static Electricity

Direct Current (DC) Electricity

Alternating Current (AC) Electricity




Overview of Energy

Kinetic Energy Concerns Movement of Matter

Potential Energy

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Thermal Energy

Thermal Energy

Thermal Potential Energy


Temperature is Average Thermal Energy

Temperature Measurement: Thermometers

Temperature Scales

Lower and Upper Temperature Limits

Equations for Temperature Limits



Heat Transfer

Heat Transfer with Hot Coffee

Heat Transfer on Earth

Heating a Greenhouse

Heat Energy Required to Turn Ice into Steam

Mpemba Effect: Hot Water Freezes before Cold

Thermal insulation

Thermal Insulation

Thermos Container Uses Thermal Insulation



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Nuclear Energy

Nuclear Reactions



Characteristics of Force

Applied Force

Applied Force Affects Motion

Mysterious Force at a Distance

Centripetal Force

Resistive Force

Resistive Force of Friction

Inertial Force

Centrifugal Force Caused by Inertia

Units of Force

Force and Torque

Fundamental Forces Act at a Distance

Pressure is Force per Unit Area

Work and Force

Work is a Result of Force

Relationship between Work and Mechanical Energy

Proof that Work Can be the Change in Kinetic Energy

Gravity and Gravitation

See the main Gravity and Gravitation menu pages.

Major topics are:

Overview of Gravity and Gravitation

Overview of Force of Gravity

Gravity Resources

Overview of Gravitation

Gravitation Resources

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Friction Force

Resistive Force of Friction


Uses of Friction

Causes of Friction

Coefficient of friction

Standard Friction Equation

Coefficient of Friction for Clean Surfaces

Coefficient of Friction for Greased Surfaces

Sliding friction

Sliding Friction

Sliding Friction on an Inclined Surface

Changing Sliding Friction on Hard Surfaces

Rolling friction

Rolling Friction

Role of Friction in Starting Rolling Motion

Rolling Friction and Automobile Tires

Traction Friction of Tires

Fluid friction

Changing Fluid Friction

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Physics Resources



Experiments and Science Fair Projects

Interactive Graded Tests


List of Champion Schools

Survey results

See results of survey questions

My books

School for Champions

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