Cycleracer Posted November 27, 2003 Share Posted November 27, 2003 Nomme, i wonder how many people have bought balloons and testing this theory. Interesting one though helium makes the balloon float which must mean that helium is lighter than air. I think the heavier air around it must cause a smll vacumm around the balloon and spin it. Oooh look at me trying to look all clever and educated. My answer is probably a load of rubbish. Link to comment Share on other sites More sharing options...
upholder Posted November 27, 2003 Share Posted November 27, 2003 Having bought my balloon this morning and tethered it to the inside of my van I now know what happens. Just kidding Ignore what I said above but it does have something to do with inertia, I think. My answer is now B. Link to comment Share on other sites More sharing options...
robh Posted November 28, 2003 Share Posted November 28, 2003 B - when the car stops EVERYTHING wants to keep moving forwards, but the air has greater weight (strictly: "mass") than the balloon (that's why the balloon floats in air) so the relatively "heavy" air moves forwards forcing the lighter balloon backwards. Link to comment Share on other sites More sharing options...
nomme Posted November 28, 2003 Author Share Posted November 28, 2003 Originally posted by robh B - when the car stops EVERYTHING wants to keep moving forwards, but the air has greater weight (strictly: "mass") than the balloon (that's why the balloon floats in air) so the relatively "heavy" air moves forwards forcing the lighter balloon backwards. Spot on. This puzzle was apparently on a show called Mindgames on BBC4. They actually did the experiment in order to prove it too. Nomme Link to comment Share on other sites More sharing options...
Carlwarker Posted November 28, 2003 Share Posted November 28, 2003 Question. The physics sounds fine, but the balloon has ‘physical’ mass. So, initially, wouldn’t the mass of air ‘behind’ the balloon, impart a force on the ‘back’ surface-area of the balloon, and tend to move it forward? Link to comment Share on other sites More sharing options...
Sidla Posted November 28, 2003 Share Posted November 28, 2003 Originally posted by Carlwarker Question. The physics sounds fine, but the balloon has ‘physical’ mass. So, initially, wouldn’t the mass of air ‘behind’ the balloon, impart a force on the ‘back’ surface-area of the balloon, and tend to move it forward? If they did the experiment to prove it, then obviously not. Link to comment Share on other sites More sharing options...
Carlwarker Posted November 28, 2003 Share Posted November 28, 2003 Originally posted by Sidla If they did the experiment to prove it, then obviously not. I suggest you read your own signature. And my question deserves an answer - not an ass-brained retort. Link to comment Share on other sites More sharing options...
nomme Posted November 28, 2003 Author Share Posted November 28, 2003 Originally posted by Carlwarker Question. The physics sounds fine, but the balloon has ‘physical’ mass. So, initially, wouldn’t the mass of air ‘behind’ the balloon, impart a force on the ‘back’ surface-area of the balloon, and tend to move it forward? I don't know. I thought it would go forward due to inertia. The actual answer I have is this : "the decelleration makes the air inside the car move forward, relative to the car, but the helium, being lighter and subject to less force, is displaced backwards by the air rushing forward" which sounds reasonable to me. With Xmas partys coming up with helium ballons about I suggest people try it out themselves. (..but I suspect people like Hodge will get to them first) Nomme Link to comment Share on other sites More sharing options...
Carlwarker Posted November 28, 2003 Share Posted November 28, 2003 Originally posted by nomme I don't know. I thought it would go forward due to inertia. The actual answer I have is this : "the decelleration makes the air inside the car move forward, relative to the car, but the helium, being lighter and subject to less force, is displaced backwards by the air rushing forward" which sounds reasonable to me. Nomme And it did to me N. But, when I considered the physical mass and surface-area of the balloon, and using Newton's Laws of Motion, then... hence, my question. Quite often, Physics 'theory' doesn't work out in practice. And, I said, initially. Link to comment Share on other sites More sharing options...
upholder Posted November 28, 2003 Share Posted November 28, 2003 Tend to agree with Carlwarker on this one. Surely if the air moves forward when the car slows down it would take the balloon with it and then move backwards when the air hits the windscreen. So the balloon moves forwards and then backwards. I did a bit of googling after my first post (yes, I need to get out more) and came across This site which offers a different explanation, vector forces, inertia etc. Also This site which gives the air movement answer and a far more technical one Link to comment Share on other sites More sharing options...
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