DevilsAdvocate

Welcome to post number 2. A thought experiment. Imagine you are a mermaid living in the middle of the ocean. You have never been to the top or the bottom. You live a happy life amongst the fishes. Who you eat occasionally. You breathe in air through your tail and you blow it out of your mouth. And life is going swimmingly. Then one day you see a couple of rainbow trout who are watching the migration of the seaweed together and suddenly you are overcome with a sense of melancholy. You go to your favourite warm spot in a cosy part of the middle of the ocean and swim there doggypaddling for a while, blowing out bubbles in front of you and watching the way they bubble about and scatter away into the distance. For some reason it becomes very important to you to understand why bubbles do that. What is it about them that does make them behave like that? It seems whatever way you blow them they have a mind of their own. This puzzles it and you think on it so long your head starts to hurt. Then suddenly, it occurs to you. That's it! Eureka! Oh little mermaid in the middle of the ocean, won't you share it with us? Yes? Thank you - Then, please, what is your mermaid theory of gravity? Please allow yourself the pleasure of becoming the mermaid for a moment and channel your response into a reply for the greater good. The Devil's Advocate

Thank you for your braintime. It's such a nice thing about the internet as opposed to the classroom that the ones who haven't got it are usually the ones to speak up. Much more effective teaching wise. A literalist may assume from my vivid descriptions that I'm talking about dropping things on earth. I'm not really. That's just fun. I'm talking about dropping things in a perfect spherical world of theory. And in this world (very much like in our world)... Unfortunately you cannot drop two objects from exactly the same place via exactly the same space and therefore the earth will approach the heavier faster, admittedly imperceptibly to all but the most gigantically miniscule pedant, such as [drum roll...] the Devil's Advocate The serious point is that what is often inferred from the lovely idea that a feather and a ton weight drop at the same rate without air resistance is that mass is not an important factor in gravity. It is. It's just that the total mass of the two objects involved (the faller and the fallen towards in most cases) is what counts. And here on earth the fallen towards always outmasses the faller by a gigantic ratio. You who have commented know this already and may see it as too obvious to bother pointing out. Which is exactly why I've pointed it out, because you're obviously the ones who explain things around here. Ta-dah! Thankyou. Devil's Advocate

Hello and welcome to my first post. I am the Devils Advocate. I do thought experiments that are just plain evil. I start with something wrong and twisted and then try and persuade you everything you know is wrong and twisted.But with no further delay... my first topic: Myth 1? Two objects fall identically due to gravity regardless of mass. Really? Interesting.You can do this one at home. 1. Take an object, an egg will do, and drop it from your outstretched hand. Observe its fall. Now clear it up. 2. Now take an imaginary egg up to the moon on a quick field trip. Do the same experiment. Drop it from the same height. Let's call it a metre in both cases. It falls to the ground, a little slower, but in a similar manner. Lets say it takes x seconds to fall on earth and 1.5x seconds on the moon. The figures don't matter, but it takes longer on the moon. Do you agree so far? YES? 3. Tell me why it takes longer for the egg to fall to the floor on the moon?-Because the earth has more mass than the moon- Therefore the moon's gravity is weaker than the earth's- Therefore the force making the egg fall on the moon is weaker, it goes slower and it takes longer. Correct? YES? 4. But if Uncle Albert taught us anything, it's to look at the bigger picture! Although within our normal frame of reference, gravity means attraction of things downwards towards earth, it doesn't actually mean that. Gravity is the force of attraction, (if that's what it is - see a later discussion, but here we're just debunking this Newtonian myth for the moment), between 2 masses. Between them. What does that mean? It means that each object attracts the other. So as well as the earth attracting the apple, the apple (to a miniscule extent) attracts the earth. Not very much obviously. But then Eve only had a little nibble and see where that got us. Apples are potent. Try one? 5. So you've dropped an egg on your kitchen floor and you've dropped one up on the moon. The one on the moon took longer to fall (and you didn't have to clean it up). And we agreed that the reason for this slower fall on the moon was the larger mass of the earth. Now I want to see what happens if we get rid of the egg and now do a control experiment with just the moon and the earth. First I'd like you to drop the moon onto the earth, from exactly a metre high. Thanks. I never liked Colorado anyway. Second, I'd like you to drop the earth on the moon from a height of exactly one metre. Thirdly I'd like you to (you may have just done this twice already) suspend the two lumps, earth and moon, a metre away from each other in space and 'drop' them towards each other. Watch what happens in each (should be pretty similar).My simple question is: do the earth and the moon fall together within the normal time for the earth (x seconds), for the moon (1.5x seconds) or longer, or shorter? 6. Hopefully you went for shorter. That is the correct answer.The earth and the moon fall together quicker than the earth and a set of car keys.Therefore if you drop the moon and a set of keys off the leaning tower of Pisa at the same time, the earth and the moon will get together before the keys get to first base. 7. Newton's gravity equation: Shows the force of attraction between two masses, m1 and m2. If you increase the mass of one, you increase the force. So why is there this myth that objects fall at the same rate regardless of mass? The difference is tiny tiny tiny obviously, because the earth is the major influence on the force. But there is a difference. You drop a heavier object and the masses involved are larger, which means the forces are larger, which means the fall is faster. 8. There is one further point to add. To do with our frame of reference. Whenever something is taken from the mass of the earth and then dropped back onto it, the total masses involved in working out the gravity are the same as if any object on earth was taken from earth and dropped on the earth. Because it is a closed system. You drop a tank on the earth, the total masses involved are that of the earth and that of the tank, which was just removed from the earth. So if you do that and then drop a mug on the earth, the total masses involved will be the same in each case, because the earth in the first case has the mass of the earth (including the mug, but minus the tank) and that is being combined with the tank. In the second, the earth has the mass of the tank included, but is missing the mug, but the earth and the mug's masses are combined to work out the fore of attraction anyway. So if you have two identical objects and you drop the first on the earth, then you get the second one from the moon where it was being stored, and you drop the second one.... it will fall ever so slightly faster than the first, even though the objects were identical. Because the total masses involved are slightly higher and therefore the gravity of earth would have increased slightly. AM I RIGHT? OR ARE THEY WRONG?