The Rules of Motion

What this book is about

Look around you. Almost everything is moving — buses running, fans turning, rain falling, a cricket ball climbing towards the boundary. Behind all that variety there are not many rules. There are three sentences, and all three are short enough to fit on a postcard.

So why does this part of physics feel so hard? Because school breaks it into nine separate subjects — equations of motion, Newton's laws, vectors, friction, projectiles, circular motion, work, energy, power. The list to memorise keeps growing, and nobody points out the single thread running through all of it. The thread is there. Page 6 has a picture of it.

This book walks the other way round: first the situation, then the numbers, and only at the end the formula. Nothing falls out of the sky — wherever a rule is needed it is built on that very page, with no step hidden. And every number in the book — every cell of every table, every bend of every curve — was worked out and checked.

What is inside

• Where you measure from, average against instantaneous, and why acceleration does not

mean "going fast"

• Vectors: adding arrows, a boat crossing a current, and motion relative to whom
• Inertia, F = ma, action and reaction, and friction — the force that was hiding
• Mass against weight, why everything falls at the same rate, and your weight in a lift
• Projectiles, stopping distance, work, energy, and one answer reached by two roads
• The people who found the rules — Āryabhaṭa's moving boat, the *mayl* carried within,

Galileo's sloping plank, the *Principia*, and where Newton's laws stop

• Two experiments to try, a formula sheet, worked exercises, a glossary and a quiz