ah.clem and infodragon write:
This story from a Wired article: NASA is a major player in space science, so when a team from the agency this week presents evidence that "impossible" microwave thrusters seem to work, something strange is definitely going on. Either the results are completely wrong, or Nasa has confirmed a major breakthrough in space propulsion. British scientist Roger Shawyer has been trying to interest people in his EmDrive for some years through his company SPR Ltd. Shawyer claims the EmDrive converts electric power into thrust, without the need for any propellant by bouncing microwaves around in a closed container. He has built a number of demonstration systems, but critics reject his relativity-based theory and insist that, according to the law of conservation of momentum, it cannot work.
NASA states... "Test results indicate that the RF resonant cavity thruster design, which is unique as an electric propulsion device, is producing a force that is not attributable to any classical electromagnetic phenomenon and therefore is potentially demonstrating an interaction with the quantum vacuum virtual plasma"
"First off, micro-Newtons is tiny."
Right off the top of my head its an appropriate measure for sunlight pressure for a medium-ish sized spacecraft. Depending on geometry and orbit (like orbit of Mercury or orbit of Neptune?) etc. Light pressure is well understood physics. The point of this experiment is screwing around with a different wavelength of EM waves. Whatever. So if it worked you're not going to the stars as designed currently, but it migth help with stabilization of large solar panel arrays. Other than I think we have a scaling problem here.
Another thing best measured in micro-newtons is some really small ion thrusters recently developed for some scientific experiment I don't remember. It turns out to be really hard to both generate and measure and control a force this small. It should be possible scientifically but its an area of engineering that has not as of yet been deeply explored. So even if its useless for "real propulsion" it might be handy for weird cutting edge scientific experiments.
Another thing I can think of that screws around in micro-Newton level is gravity of "human industrial objects". A couple thousand pounds of junk vs a couple hundred pounds of junk at a close-ish range is sorta on the scale of micronewtons. Yeah yeah 10 Kg 10 M apart is like a nanonewton which is a thousandth too small. Luckily things can be closer together than 30 feet and industrial objects can be way heavier than a thousand times a kilogram. The biggest unit object I ever had access to (although as IT guy, I never used) was an industrial metal lathe about 100 feet long by 10 feet high used to build crane shafts or some such thing and as a rough estimate the gravitational force between me and that lathe could be reasonably expressed in micronewtons.
If you want to play angular games for fun, run the trig analysis of if I weigh a reasonable amount of newtons and my feet are a foot apart, then micro newtons to the left or right represent one foot being a ridiculous amount higher or lower than the other foot. Estimate in my head well below the thickness of a piece of paper. So any measurements require much better than "ah its just kinda flat looking" or "Seems level cause it's kinda lined up with pix on the wall"
A final micro-newton scale situation I can think of would revolve around sound. I'm having a hard time estimating based electrically making some assumptions about speaker efficiency (which is never as high as people think) but I think micronewtons of force on the speaker in my subwoofer would be quite inaudible across the room yet micronewton forces on the speaker in my mother in law's hearing aid in her ear "could be" audible plus or minus the reason she's wearing the hearing aide. I think it would be out of thermal noise range but not entirely sure.
I'm just trying to take the measurement outta technobabble land and into "and this is why its an engineering challenge to measure" land.