Quote Originally Posted by Gavinfoxx View Post
I'm also totally confused with the

Newton-Meter or Foot-Pound
vs
Newtons or Pound Force

thing. What DO I want to answer 'how good is this thingy at pushing a boat?' question?
Newton-Meter and Foot-Pound are energy.

Newtons and Pound force, are force. Force is a unit for how much something is being pushed. Energy is a measurement of how much total pushing (over a time interval) something has received, or is capable of giving. You want Newtons or Pounds.

Also,

Okay, for this link: http://www.enworld.org/forum/d-d-leg...ess-water.html

Lets go in order

Post #9: http://www.enworld.org/forum/1638728-post9.html

treats water as having density of 1kg/m^3, is off by a factor of 1,000, so his answer should be F=450N, rather then 0.45N

also, he goes from having diameter of 4.5cm, to a radius of 4.5cm (typo I assume), putting off by a further factor of 4. Not sure about his water container height thing. I can pull out my physics text book and check if you really want

post #11: http://www.enworld.org/forum/1638759-post11.html

makes the assumption that water, if shot straight up, would go 20ft in the air, as per item description. Figures out area of nozzle from there. While we assumed area of nozzle, and ignored that 20ft thing cause it made 0 sense.

He got 4172 lb-ft, which, no matter which definition of pound you use (mass or force), is NOT a unit of force.
4172lb = 18,558N for reference though.

Problem is, he miscalculated velocity. He got 100ft/s, which would, with 32.2ft/s^2 gravity, cause the stream to hit 155ft. For comparison, the actual water velocity would be ~10.8m/s=35.6ft/s

Second problem is, he confused the pound (mass), with the slug (another empirical unit of measurement for mass). Which caused him to be off by a factor of 32.2.

Adjusting for those, the actual force given his assumptions is:
~46.1lb ~= 205N

Post 13: http://www.enworld.org/forum/1638825-post13.html

differing assumptions, however, given his assumptions, his math is correct as far as I can tell.

Post 19: http://www.enworld.org/forum/1639087-post19.html

fixes the wrong velocity problem in post 11, doesn't fix the pound-mass != slug problem

will look at the rest later. But basically the 200N~500N range seems to be the most consistent/realistic (if you want pounds, type "convert xxx newtons to pounds" into google, replacing xxx with a number)