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revolution
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revolution
sleepsleep wrote:
a DVD under a second!!!!! over 1km
Wow. That means the DVD is travelling at 3600km/h. Sounds extremely dangerous. I wouldn't want to be in the way when that is travelling, it would slice my head off. Wink

"Pull"
Post 21 May 2013, 11:46
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HaHaAnonymous



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Last edited by HaHaAnonymous on 28 Feb 2015, 20:24; edited 1 time in total
Post 21 May 2013, 13:58
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revolution
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revolution
HaHaAnonymous wrote:
Quote:
I wouldn't want to be in the way when that is travelling, it would slice my head off.

I doubt very much. The DVD is too fragile for this. I bet it would break in many pieces (maybe while still on air).
Does it break before or after it has sliced off my head? Not that it matters really, even one small piece at that speed would be sufficient to cause the body|head separation scenario.
Post 21 May 2013, 14:08
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HaHaAnonymous



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Post 21 May 2013, 14:16
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malpolud



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malpolud
Why would it break traveling that fast? If it is not spinning it has no reason to break Smile
Post 21 May 2013, 14:57
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revolution
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revolution
malpolud wrote:
Why would it break traveling that fast? If it is not spinning it has no reason to break Smile
If it is not spinning then it will tumble. I think spinning would be the best possible way to get it to complete the 1km journey. Just the same as a bullet works best with a rifled barrel to give it spin and improve its accuracy.
Post 21 May 2013, 15:06
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malpolud



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malpolud
Hmm, you are right about the spinning movement. It would help keeping the axis of rotation at the same angle, even though the rotation of a dvd would take place in different plane than the bullets.

But, we could give the DVD quite a lot of linear speed and just a little bit of angular velocity.

HaHaAnonymous while counting the kinetic energy of the dvd don't forget to include both vectors of motion Wink
Post 21 May 2013, 15:24
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sleepsleep



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sleepsleep
somwhow i think, it is possible if dvd travel above water,

O______
Post 21 May 2013, 15:43
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DOS386



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malpolud wrote:
Why would it break traveling that fast? If it is not spinning it has no reason to break Smile


Smile just melt Smile
Post 22 May 2013, 04:41
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revolution
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revolution
Hmm, this is an interesting problem.

I wonder if a DVD will melt or not. It can only melt if the temperature is high enough. The way the temperature will increase is if the air on the leading edge is compressed (adiabatic heating). The energy supply for the heating is the momentum of the DVD (i.e. it slows down and trades momentum energy with heat energy). The total momentum of a DVD is very small and it might have enough momentum to compress enough air to cause the leading edge to melt. And since the DVD needs to be spinning then I expect only the outer rim to heat up leaving the inner portion undamaged. The transfer of heat from the edge to the centre would be slow and I doubt that within the one second of flight time that the centre would even heat up at all. Indeed the centre portion might reduce in temperature due to air cooling (think about how a windy day makes you cooler).
Post 22 May 2013, 10:14
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malpolud



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malpolud
Well I rather doubt there is going to be any adiabatic heating up there, cause the whole system won't have thermal insulation with surrounding. There is no insulation between the air in front of the CD and the rest of the air.

The reason why this object could be heated will be friction between air particles and the DVDs particles, and between air particles very near to the DVD.

Did anybody found out whats the speed or distance record while throwing/shooting the DVD?
Post 22 May 2013, 15:22
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HaHaAnonymous



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Last edited by HaHaAnonymous on 28 Feb 2015, 20:23; edited 1 time in total
Post 22 May 2013, 15:35
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malpolud



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malpolud
Well, through the years I am alive, I have observed how do different things interact together. Moreover thanks to the humans brain that I carry into my head, I can approximate the distance on my own. I'd rather see some official records like these from Guinness Book.

BTW: 80km/h wind won't let you walk or even stand, not to mention throwing a DVD Smile 100 meters seem doubtful too.
Post 22 May 2013, 16:23
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Post 22 May 2013, 16:39
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revolution
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revolution
malpolud wrote:
Well I rather doubt there is going to be any adiabatic heating up there, cause the whole system won't have thermal insulation with surrounding. There is no insulation between the air in front of the CD and the rest of the air.
Remember it is travelling at 3600km/h and the only source of heating will be adiabatic compression. Although as I suggest above I doubt there is enough energy in the system to melt the DVD before is comes to rest due to frictional forces.
malpolud wrote:
The reason why this object could be heated will be friction between air particles and the DVDs particles, and between air particles very near to the DVD.
Oh? I was always taught that the frictional heating is much less than the airspeed cooling, thus an overall cooling effect for any moving body though air. Of course this is in opposition of adiabatic heating which is only relevant on the leading edge of an object moving at very high speed. At low speeds adiabatic heating is almost non-existent, but becomes significant once the speeds become higher.
Post 22 May 2013, 17:00
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malpolud



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malpolud
Could you provide source for that concerns, because I am not sure about that adiabatic heating part.
Post 22 May 2013, 19:59
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matefkr



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Jebus Christ.
Post 22 May 2013, 22:12
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revolution
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revolution
malpolud wrote:
Could you provide source for that concerns, because I am not sure about that adiabatic heating part.
Why do fans cool your PC? Because moving air will take away heat as it passes.

Adiabatic compression (and thus heating due to Boyle's law) is why the space shuttle needs ceramic tiles, not because of air friction.
Post 23 May 2013, 03:09
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malpolud



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malpolud
Ok, but according to http://en.wikipedia.org/wiki/Drag_%28physics%29 the Image the force increases in the square of the velocity. Bigger forces, more work is done, more work, more heat. As at low speed the effect of air cooling is stroger than the heating effect at higher speeds it could be on the contrary. The equation works for fluids, and most of fluids are uncompressible therefore there is no adiabatic compression in this case that could cause the square increase of the force.

If I am wrong please correct me. Some scientific evidences would be welcome, cause the topic is quite interesting. I could not find any information on the topic and that is why I am asking for source. It is obvious that gas is compressed in the front of a fast moving object. I am not sure if in this case we can talk about adiabatic compression, cause I don't know if the condition of adiabatic insulation is met (the air is free, and is not compressed for ever, it gets compressed in the front and decompressed after than).
Post 23 May 2013, 17:25
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gabiz_ro



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gabiz_ro
Woaw,supersonic DVD
2.9387 Mach
Post 27 May 2013, 12:44
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