Kinetic and Potential Energy | Nothing Is Ever Used Up | IGCSE & O Level Physics

inetic and gravitational potential energy explained for IGCSE and O Level Physics — the two stores, the exchange between them, and why nothing is ever used up. Part 11 of the series, and the second of the energy thread. Covers Cambridge IGCSE 0625, Cambridge O-Level 5054 and Singapore-Cambridge 6091. Drop a ball from 1.25 m. It comes back to 0.75 m, then lower, then lower again, and after a few seconds it is sitting on the floor doing nothing. The battery goes flat. You are out of energy by nine o'clock. So it looks like energy gets used up — and the ball really does stop, so you are not imagining it. The word that is wrong is "gone". Energy sits in STORES and moves between them along ROUTES, and mixing those two lists up is the commonest wording error in the topic. "Heat energy", "sound energy" and "electrical energy" are not stores at all. Lift the 20 kg bag from last episode and you did 200 x 1.5 = 300 J of work on it. Those joules did not vanish — they are stored in the bag because of where it is. Work done ON it is energy stored IN it, and writing that in letters gives Ep = mgh. Drop a 0.4 kg football from 1.25 m and it holds 5 J up there and 5 J of motion at the floor. Set the two equal — mgh = 1/2 mv squared — and the mass cancels: v = the square root of 2gh. There is no m in that line, which is why a football and a medicine ball land together. The real ball comes back to 0.75 m, so 3 J. Two joules are unaccounted for. They are not missing — they are in the floor, the air and the ball, shared between more particles than you can count, every one going a different way. There is nothing left to push. CHAPTERS 0:00 Drop a ball 0:29 Before I tell you anything 1:01 Where energy sits 1:50 Lift it and you fill a store 2:49 Potential energy, defined 3:03 Anything moving has kinetic energy 3:35 Kinetic energy, defined 3:55 Drop it — the exchange 4:18 Set them equal, and the mass goes 4:49 Nothing in that line mentions the mass 5:58 Conservation of energy, defined 6:23 It comes back lower 6:54 What internal energy is 8:07 Sixty per cent 8:23 Five places energy changes store 8:39 A reservoir 9:09 A rollercoaster 9:47 A pile driver 10:18 A pendulum clock 10:53 A car braking 11:22 Where each one ends up 12:16 All of it, on one slide 12:53 Why it stopped bouncing 13:21 BONUS: where the square and the half come from 14:49 Next: pressure WORK THROUGH IT YOURSELF Notes, all three definitions in the wording the exam wants, the five places with their numbers worked, why a pile driver's small number does a big job, what internal energy actually is, and three practice questions with the answers held back: https://claude.ai/artifact/8aV4Pbjf59... WHAT IS COVERED kinetic energy — gravitational potential energy — Ek = 1/2 mv squared — Ep = mgh — conservation of energy — energy stores and transfer routes — internal energy — efficiency — v = the square root of 2gh — why the mass cancels All three definitions are given in the wording examiners mark, with the trap named next to each. h is the CHANGE in height, not a position. Square the speed BEFORE you multiply, and do not drop the half. And energy is never created or destroyed — only transferred from one store to another. STORES AND ROUTES Stores are where energy sits: kinetic, potential (gravitational, chemical, elastic), nuclear, internal. Routes are how it moves: mechanically (a force moves something — that is work), electrically, by heating, by waves. So "heat energy", "sound energy" and "electrical energy" are not stores. They are how energy travels, and where it lands is almost always the internal store — something, somewhere, is a bit warmer. FIVE PLACES, ONE EQUATION EACH A reservoir: 1 cubic metre of water 50 m up is 1000 x 10 x 50 = 500 000 J. A rollercoaster: 500 kg dragged 40 m up is 200 000 J, and arrives at 28 m/s. A pile driver: a 2000 kg hammer dropped 3 m is 60 000 J, delivered in a tenth of a second. A pendulum clock: a 5 kg weight falling 1 m over a day is 50 J — about 0.6 of a milliwatt. A car braking: 1500 kg at 20 m/s is 300 000 J, straight into the brakes. BONUS AT THE END Why the speed is squared, and where the half in 1/2 mv squared comes from — done with the area under a speed-time graph, no algebra. Optional, and the slides say so. ASK If anything did not land — any slide, any step — ask in the comments and say which slide. I answer every question, and there is no such thing as a question too basic. PREVIOUS EPISODE https://www.youtube.com/watch?v=YOUR-... NEXT Pressure. Work out the pressure under a stiletto heel and then under an elephant's foot, and the heel wins — it is not close. And the equation behind it has no volume in it and no shape, which is the same trick you just watched with the mass. Subscribe and it reaches you when it lands. Physics for Cambridge IGCSE 0625, Cambridge O Level 5054, and Singapore GCE O Level 6091 (Singapore-Cambridge SEC K323 from 2027). #physics #olevelphysics #igcsephysics