Simple Physics?

geuben said:
I have a serious lack of sleep and a messed up body clock, but I stand by it not being there :p

Edit: also, i have almost 3/4 of an electronic engineering degree, yet I still say silly things when it comes to electronics.
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lol, that's the difference right there you see, I have a whole Physics degree:D

p.s. seriously, there was no edit.
 
Seen as how you have a physics degree, do you know anything about EHD thrusters? The little tin foil things that hover using electricity?
 
I have seen them, but I didn't have any modules or experiments specifically on the effect. Electronics was not a huge part of my degree syllabus, although I had to do a bit in my final year project. Why do you ask?
 
geuben said:
Because you are also moving forwards at the same speed as the train, if you could stay in the air long enough you would start to slow down relative to the train and would end up further back than you started.
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Not true I'm afraid. An easy way to think of it is that any object with mass doesn't change velocity by itself, it has to be acted on by another force. So when you jump up in the air you continue to move with the same horizontal velocity, no matter how much time you spend there. This is because there is nothing pushing you to the back of the train. If you were standing on a train with no walls (was open to the environment) you would be hitting lots of air that was not moving with the train, on the train it would appear that the air was pushing against them blowing them off the back of the train. Now if you jump up you are slowed down, because the air pushes against you as you move into it. This affect will slow you down and you would appear to move backwards towards the back of the train.

All of this of course assumes the the train is moving at constant velocity.
 
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I was just curious. There are lot of videos on youtube of peoples homemade ones, and quite a lot of website on them. What i wondered was, what are the limiting factors to them? All the ones ive seen are all made of balsa wood and tin foil to be really light. Could you make a heavier one and just pump more voltage through it to create more lift? Also somewhere suggested that using a dielectric could increase the effect (like a capacitor). Basically i just wanted to know if this method could realistically be used to create a hover car or similar.
 
yak.h'cir said:
Not true I'm afraid. An easy way to think of it is that any object with mass doesn't change velocity by itself, it has to be acted on by another force. So when you jump up in the air you continue to move with the same horizontal velocity, no matter how much time you spend there. This is because there is nothing pushing you to the back of the train. If you were standing on a train with no walls (was open to the environment) you would be hitting lots of air that was not moving with the train, on the train it would appear that the air was pushing against them blowing them off the back of the train. Now if you jump up you are slowed down, because the air pushes against you as you move into it. This affect will slow you down and you would appear to move backwards towards the back of the train.

All of this of course assumes the the train is moving at constant velocity.
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Yeah, i added the bit about the air moving also in afterwards and didnt really change my post to make sense. oh well its late. also saying you won't move backwards if you jumped for long enough also assumes that no force (from moving air in the train) acts upon you when you are airborne.
 
geuben said:
I was just curious. There are lot of videos on youtube of peoples homemade ones, and quite a lot of website on them. What i wondered was, what are the limiting factors to them? All the ones ive seen are all made of balsa wood and tin foil to be really light. Could you make a heavier one and just pump more voltage through it to create more lift? Also somewhere suggested that using a dielectric could increase the effect (like a capacitor). Basically i just wanted to know if this method could realistically be used to create a hover car or similar.
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From what I have just read, I get the impression that the voltage requirements would be pretty immense. If it's taking kV/MV to lift a pice of foil, the requirements for something the weight of a car are going to be 1000 fold, if the thrust generated is proportional to voltage.
 
SpeedFreak said:
From what I have just read, I get the impression that the voltage requirements would be pretty immense. If it's taking kV/MV to lift a pice of foil, the requirements for something the weight of a car are going to be 1000 fold, if the thrust generated is proportional to voltage.
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Yeah that's what I thought, the dielectric looked promising from the results i saw, but it didn't increase the effect enough to make it realistic to make one powerful enough to lift a car. oh well, looks like i'll have to find a new way to make a hover car :p
 
Thinking of that thruster, it would make a cool CPU cooler. As quiet as passive cooling, but can create airflow.
 
Dist said:
Thinking of that thruster, it would make a cool CPU cooler. As quiet as passive cooling, but can create airflow.
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You want to put something thats got 20,000 volts running through it that close to your cpu? Its arcs really easily and will fry your whole pc. plus from all the videos they make a loud buzzing noise, but i think that might be the powersupplies.
 
geuben said:
You want to put something thats got 20,000 volts running through it that close to your cpu? Its arcs really easily and will fry your whole pc. plus from all the videos they make a loud buzzing noise, but i think that might be the powersupplies.
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it doesnt have to be powerfull enough to lift its own weight though, it just has to be powerfull enough to create airflow.
 
Dist said:
it doesnt have to be powerfull enough to lift its own weight though, it just has to be powerfull enough to create airflow.
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To create any sort of effect they still require lots of volts. Plus it's ionised air flow, i personally wouldn't want it near my pc.
 
geuben said:
To create any sort of effect they still require lots of volts. Plus it's ionised air flow, i personally wouldn't want it near my pc.
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why not? i remember on /. about a year ago someone made some sort of ionised airflow cooler for his pc and it worked fine. Didnt work the same as this tin foil and copper wire one though, but it had the same effect.
 
Dist said:
why not? i remember on /. about a year ago someone made some sort of ionised airflow cooler for his pc and it worked fine. Didnt work the same as this tin foil and copper wire one though, but it had the same effect.
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Humm...wouldn't mind seeing that, i was under the impression that ionised air was 'bad' around electrical items, and along with the high voltage had the potential to shock eveything....kinda like lightening.
 
geuben said:
Yeah, i added the bit about the air moving also in afterwards and didnt really change my post to make sense. oh well its late. also saying you won't move backwards if you jumped for long enough also assumes that no force (from moving air in the train) acts upon you when you are airborne.
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Well unless some idiot left a window open (it is winter after all!) then the forces due to the air hitting you should balance.
 
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