Can you handle Physics 11?

So should we dust off the ol' conveyor belt or what?

it won't take off, lift comes from airspeed over the wing, since the plane is not moving relative to the air around it, there is no airspeed, and no lift. i am pretty darn sure that is the case now.

I hope you guys know that physics is based on known law. Noooooot much up for debate.

Any physicists here?

My physics is very poor, but if I remember correctly thrust is a function of velocity and mass of the ejected material. So if you are constrained by the velocity, which is defined by a maximum PSI (subject to the size of the nozzle), could you improve matters by increasing the mass of your propellant, i.e. by dissolving a shit load of salt or sugar in it?

supersaturated solutions can be made easily by heating the right salt or water soluble compound in water. I think you can increase the density of a salt solution over pure water by almost 20%, which may (?) give you more thrust. But would the extra weight negate this effect, that's why I need a physicist to chip in.

The salt solution may not be as slippery as regular water, add some detergent (only a touch)?

Maybe worth experimenting?

Some other info here:

http://en.wikipedia.org/wiki/Water_rocket

Please post video of best launch

Yes the fins do not work very well, but I wanted to have something together so I can test it out a bit.
I ended up with this, but I have no problem ripping it apart tomorrow. Pull the fins and install a string? Heavier weight? Shorten the rocket? (I have no more bottles so it can't get longer)

More sticker to sharpie ratio? Just more sharpie in general? Write NBR in sharpie on the side?

I designed it off a rocket I saw in a movie once:

I don't really know about the water/air pressure thing, I'm more worried about a straight flight with minimal drag than I am about increasing the original acceleration (other than making it as light as possible).

your rocket looks like a nipple at the top, one down below looks like a dick

i think it has to do with the venturi effect, narrow opening, higher velocity of propellant. if you had a big opening like you suggest…

Sounds like you're explaining why a narrow eurethra isn't a bad thing, Hank.

air has mass.

i think it has to do with the venturi effect, narrow opening, higher velocity of propellant. if you had a big opening like you suggest, the force would be applied over a short time, and the rocket would go nowhere.

If he could maintain the pressure,you're idea might work…but the pressure will be dropping as water is released,therefore providing less thrust to the rocket as it still carries fuel

Less thrust but less weight too.

Any physicists here?

The salt solution may not be as slippery as regular water, add some detergent (only a touch)?

in the world record video above, he used a 33% solution of dish soap in with his water.

Modifying the opening from higher up is a good idea, but the tube used to pressurize the rocket is too long, I would have to start modding from halfway up the rocket. Only way i could think of would be to add tape around the inside of the exit hole so that it would be pushed up and out of the way by the tube, but move down and block a bit of the exit hole when the water started to come out, but I'm not even sure that it will benefit the rocket if Oxymoron's right.

Adding dish soap sounds good, but might also be frowned upon (deemed as cheating) which would result in a fail.

And nipple's great, to put it scientifically; Boobs [HTML_REMOVED] Dick any day :P.

The best thing you can do is to get out and test different ideas ahead of time. Theory and speculation are good starting points but you'll get further faster with real world experimentation. You're going to make mistakes when your designing something. The trick is to make them early, adapt and move on.

Build several design, try messing with the mass of the propellant as Knnn suggested, basically experiment.

I would also ask your teacher about stuff, like the dish soap, ahead of time. The worst that can happen is he/she says no, but you could have a great advantage over your competition if he/she OK's it. I would also discuss all your ideas with the teacher. They're trying to teach you something and will likely give you some good feedback on what will/won't work.

nice try with the ventury effect droppage. Unfortunatly thrust does not equal the velocity of the water leaving. Its a function of the water and the mass flow rate out. Thus more mass slower, or less mass faster could both be possibilities for the most force. You want to get rid of all your water ASAP otherwise your just going to use all of your force lifting useless water. After the first instant boom the pressure won't be enough to sustain a thrust anyways.

Gotta think more like a jet engine and less like a running pipe, kind of like the question on my third year fluids course today…

n You want to get rid of all your water ASAP otherwise your just going to use all of your force lifting useless water. After the first instant boom the pressure won't be enough to sustain a thrust anyways.

Yeah,everybody listen to the 3rd year fluids student and not the guy who said the same thing a deals with high pressure hydraulics everyday.

Kevin m31 is right,and so am I.

So,what was the result?

Went the farthest in my class, so I was stoked! But someone used pop cans for fins (aluminum) instead of plastic and managed to get a little farther then me (lined them up way better and eliminated all drag), so not bad but coulda' been a little better :P. Thanks for all the help guys!