Newtonian Physics: Laws of Motion & Light
From the Principia Mathematica to his optics work, Newton's mathematical approach to nature built the foundation of modern physics and changed how we see motion, gravity, and light.
Mathematical Principles
Principia Mathematica: The Mathematical Foundation of Physics
Published 5 July 1687
Newton's Philosophiæ Naturalis Principia Mathematica revolutionised natural philosophy by demonstrating that the same mathematical laws govern both terrestrial motion and celestial mechanics. The work established that universal gravitation follows an inverse square law, unifying the physics of falling apples and orbiting planets.
The Principia introduced Newton's three laws of motion, providing a mathematical framework that remained unchallenged until Einstein's relativity. The work's geometric demonstrations showed how mathematical analysis could reveal the fundamental principles underlying natural phenomena.
The Laws of Motion
First Law: Every body continues in its state of rest, or of uniform motion in a straight line, unless compelled to change by forces impressed upon it.
Second Law: The change of motion is proportional to the motive force impressed, and is made in the direction of the straight line in which that force is impressed.
Third Law: To every action there is always opposed an equal reaction, or the mutual actions of two bodies upon each other are always equal and directed to contrary parts.
"Breaking down Proposition I, Theorem I from the Principia helped my A-level students grasp the leap from Kepler's observations to Newton's proof of universal gravity. This resource makes Newton's geometric reasoning clear for modern learners."
Experimental Optics
Newton's Opticks: The Science of Light and Colour
Published in 1704, Newton's Opticks presented his experimental investigations into the nature of light and colour. Unlike the geometric demonstrations of the Principia, this work employed empirical methodology, describing controlled experiments that could be replicated and verified by other natural philosophers.
Newton's prism experiments showed that white light is made of a spectrum of colours, overturning the idea that colour was just altered white light. His careful work made optics an experimental science based on precise measurement and math.
The Prism Experiment
Setup: Darkened room with small aperture allowing sunlight to enter and strike a triangular glass prism
Observation: White light separates into spectrum of colours (red, orange, yellow, green, blue, indigo, violet)
Conclusion: White light is composite, containing all colours; the prism reveals rather than creates colour
Verification: Second prism recombines spectrum back to white light, proving the analysis
Revolutionary Approach
From Natural Philosophy to Mathematical Physics
Mathematical Analysis
Newton created calculus (his "method of fluxions") to analyze changing quantities, which let him calculate planetary orbits, projectile paths, and tidal forces precisely.
Experimental Verification
Each theoretical proposition in the Opticks was supported by controlled experiments that other investigators could replicate, establishing the principle of empirical validation.
Universal Principles
By demonstrating that the same laws govern terrestrial and celestial phenomena, Newton showed that nature operates according to universal mathematical principles.
Newtonian Reflecting Telescope
Newton's design eliminated chromatic aberration by using a curved mirror instead of lenses, providing clearer astronomical observations and practical application of his optical theories.
Triangular Glass Prism
The simple prism became Newton's primary tool for investigating the composition of white light, demonstrating how controlled experiments could reveal fundamental properties of nature.
Scientific Revolution
The Newtonian Synthesis
Annus Mirabilis
During the plague years, Newton developed his method of fluxions (calculus), formulated the law of universal gravitation, and conducted his prism experiments—laying the foundation for modern physics.
Principia Published
The Principia demonstrated that celestial and terrestrial mechanics follow identical mathematical laws, unifying physics and establishing the scientific method as the foundation of natural philosophy.
Opticks Published
Newton's experimental investigation of light established optics as a mathematical science and demonstrated how controlled experimentation could reveal the fundamental properties of natural phenomena.
Study Newton's Original Works
Access digitised manuscripts, mathematical demonstrations, and experimental notebooks documenting the development of classical mechanics and optics.