Mass and Weight: What's the Difference? | Free Fall | IGCSE & O Level Physics

Mass and weight are not the same thing, and a heavy object does not fall faster than a light one. Free fall, gravity, air resistance and terminal velocity, explained for IGCSE and O Level Physics. Drop a coin and a sheet of paper and the coin wins every time. You have seen it. You were right about what you saw — what is wrong is what almost everyone decides it means. Gravity really does pull harder on a heavier object. That part is true, and it is why the wrong answer has lasted two thousand years. But a heavier object also takes more force to get moving. Both sides double together, so the acceleration never changes. Crumple one of two identical sheets of paper and it beats the flat one to the floor, with exactly the same mass. Nothing about the amount of matter changed. Only the shape did — and shape only matters because of the air. Put the two ideas you already have side by side and the whole thing falls out in one line: a = F / m, and W = m g, so a = m g / m = g The mass sits on the top and on the bottom, so it cancels, and what is left has no mass in it at all. Everything falls at the same rate. It was never the weight — it was always the air. In 1586, two men in Delft dropped two lead balls from a tower and did not watch them land. They listened. One thud, not two. Chapters: 0:00 A coin and a sheet of paper 0:18 Why that answer is reasonable 1:00 Aristotle, and twice as heavy 1:40 Crumple the same sheet 2:29 Same mass, different behaviour 2:46 The only thing you changed was its shape 3:06 Air resistance, or drag 4:04 Weight, and why it is not mass 4:31 Mass on the moon, weight on the moon 5:06 Inertia 5:24 Why the mass cancels 6:19 Newton's second law 7:15 g, and what the number is 8:01 Free fall, defined 8:28 Galileo's argument 9:53 Delft, three years earlier 11:02 Take the air away 11:43 Apollo 15, on the moon 12:09 So: does a heavy thing fall faster? 12:40 A skydiver, and what free fall is not 13:46 Terminal velocity 14:38 A raindrop from 2 km up 15:18 A mouse and a horse 16:03 A parachute 16:42 Mars 17:39 Something to take away 18:06 Next: force, mass and acceleration WORK THROUGH IT YOURSELF Notes, worked examples, the eight definitions in the wording the exam wants, and a ten-question self-test with the marks broken out, so you can see exactly where each one sits: https://claude.ai/artifact/APPsm37ZKo... Do the self-test again tomorrow rather than twice tonight. Coming back to something after you have half-forgotten it is what makes it stick. WHAT IS COVERED mass — weight — air resistance — inertia — Newton's second law — g — free fall — terminal velocity Every definition is given in the wording examiners mark, with the common trap named next to it. Weight is a force in newtons, not a mass in kilograms. Acceleration is the rate of change of velocity, not just a change. At terminal velocity the forces are not absent — they are equal, and it is the resultant that is zero. A NOTE ON g There is no single exact value. It depends where you are standing. Singapore papers take 10 m/s², Cambridge papers use 9.8, and 9.80665 is a reference value a committee agreed on in 1901 — not something anyone measured to five decimal places. In an exam, use the number the paper gives you. NEXT Newton's second law. You already have the equation. Having it is not the same as believing it — because you still think a steady push gives a steady speed, and it does not. SUDDENLY OBVIOUS Physics for Cambridge IGCSE 0625, Cambridge O Level 5054, and Singapore GCE O Level 6091 (Singapore-Cambridge SEC K323 from 2027).