Single mother in need of explanation
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Posted by Dumb_Blonde on March 13, 2007, 6:07 pm
Please log in for more thread options Thank you in advance for your time. I found a neat project to do with my 14 year old son, but would like to know the science behind it so it will be educational. Here is the video link. http://www.metacafe.com/watch/470767/firecracker_rocket_project_experiment/ It is a fire cracker experiment, and I know he will love it, but I am clueless as to how this makes my car run. | |||||||||||||||||||||||||
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Posted by Homer J Simpson on March 13, 2007, 6:24 pm
Please log in for more thread options See HowStuffWorks.com | |||||||||||||||||||||||||
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Posted by DaveC on March 14, 2007, 4:07 am
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> Thank you in advance for your time. I found a neat project to do with
> my 14 year old son, but would like to know the science behind it so it > will be educational. > > Here is the video link. > > http://www.metacafe.com/watch/470767/firecracker_rocket_project_experiment/ > > It is a fire cracker experiment, and I know he will love it, but I am > clueless as to how this makes my car run. If you just put a can on the ground and light the fire cracker, the can will go a little way up in the air. If you put the can in a little larger can filled 2/3 with water, the water acts as a seal, keeping escaping "exhaust" of the explosion from leaking out. This extra exhaust increases the lift of the can, boosting it higher than if no water was used. Hope that helps... Enjoy. I remember such things (model rocket launches) as a boy. What fun! -- DaveC me@bogusdomain.net This is an invalid return address Please reply in the news group | |||||||||||||||||||||||||
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Posted by DaveC on March 14, 2007, 12:55 pm
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> It is a fire cracker experiment, and I know he will love it, but I am
> clueless as to how this makes my car run. Think of your car's engine (let's say it is a 4-cylinder engine) as 4 cans (called pistons in car-speak) with firecrackers. Then tie each can to a crankshaft with connecting rods (!). When each firecracker explodes, it pushes the piston down which, in turn, turns the crank shaft. With 4 (or 6 or 8 or 10) depending on the design of your engine), this results in a relative smooth translation of exploding gasoline (rather than firecrackers) into motion. I like this little video that shows graphically how an engine works: <http://www.youtube.com/watch?v=WPzPv-tT4BI>
The blue stuff is gasoline and air coming into the cylinder. The brown stuff is exhaust. Note that when the "bang" happens the piston goes down. *That's* how cans'n'firecrackers work like a car engine! Well, roughly... Enjoy, -- DaveC me@bogusdomain.net This is an invalid return address Please reply in the news group | |||||||||||||||||||||||||
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Posted by John Popelish on March 13, 2007, 8:06 pm
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Dumb_Blonde wrote: > Thank you in advance for your time. I found a neat project to do with
This is not so much a fire cracker rocket is it is a fire
> my 14 year old son, but would like to know the science behind it so it > will be educational. > > Here is the video link. > > http://www.metacafe.com/watch/470767/firecracker_rocket_project_experiment/ > > It is a fire cracker experiment, and I know he will love it, but I am > clueless as to how this makes my car run. > cracker cannon. A rocket gets its propulsive force by having a high pressure gas accelerate out the back. Any mass being accelerated requires a force. The force generated in the rocket engine that accelerates the exhaust out one direction, also puts the same force on the rest of the rocket, pushing it in the other direction. A cannon builds up gas pressure in a small volume inside a barrel, and that pressure pushes the projectile out the end of the barrel, while also pushing the other way on the cannon. There are action and reaction forces in both cases, but a rocket normally does not involve the containing barrel that holds the pressure till the projectile escapes the muzzle. In this case, the telescoping outer and inner can form the containing barrel, and the water forms a seal between them. The fire cracker goes off, essentially instantaneously (before the top can can move or the water get pushed out pf the way), increasing the pressure in the small volume above the water, inside the inverted can. That pressure is what accelerates the can upward as it slides out of the water. If you had a wire mesh or some other loose and open structure to hold the top can in place with just a bit above the water line, the result is almost the same, since it is mostly the mass of the water inside the top can the pressure pushes against while the top can takes off, not so much the sides of the bottom can. But proving that this is the case by trial would make for an interesting experiment. So don't take my word for it. You could probably get a much more detailed explanation in the sci.physics newsgroup. | |||||||||||||||||||||||||
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> my 14 year old son, but would like to know the science behind it so it
> will be educational.
>
> Here is the video link.
>
> http://www.metacafe.com/watch/470767/firecracker_rocket_project_experiment/
>
> It is a fire cracker experiment, and I know he will love it, but I am
> clueless as to how this makes my car run.