6 ms·

What's more wrong about inches than knots?

• Terribledactyl 10y ago
  If taken literally the dimensionality is odd. Pressure is a force applied to an area (force/2-d), and that's just a length 1-d (as written)
  • gizmo686 10y ago
    Even if not taken literally, the particular unit of "inches" is largly meaningless in this case. All we know (assuming the obvious mechanism of measurement) is that the air pressure in <choice of force units> is linear to the reported value. The conversion factor is dependent on the instrument itself (surface area, internal resistance, etc) although there may be a standard that is known specialists.
    • tlb 10y ago
      Inches of mercury -- the pressure exerted by a column of liquid mercury that high.
  • labster 10y ago
    It is a 1-D measurement. It's the pressure exerted by the atmosphere that would raise a column of mercury that 1-D length up a vacuum at 1g of gravity.
    • caf 10y ago
      It doesn't matter that you're measuring it in an odd way - pressure still has units of force per unit area. 1 "inch Hg" is 3386 Nm⁻². The fact that you can express length as "number of football fields" doesn't make length dimensionless.
  • qbrass 10y ago
    Two square inches of mercury an inch tall weights twice as much as one square inch of mercury an inch tall. But there's twice as much area, so it's applying the same amount of force to each square inch. The point is you care about the force, but don't care about the area, and a tube of mercury factors out the area.
• labster 10y ago
  Knots are one Nautical mile per hour, and 1 Nmi == 1 minute of latitude. Nautical miles are based on the shape of the earth and are thus independent from the rest of the US unit tragedy. And quite useful in navigation.
  • jdavis703 10y ago
    Well to be honest America got these units from the British. Not every tragedy is America's fault.
    • Aeolun 10y ago
      The tragedy is that they're still used now. Not that they were once used.
      • epimetheus 10y ago
        Yet, the British still use "stone" to measure their weight, then complain about universal standards not being used by the Americans.
  • bcatanzaro 10y ago
    Of course, the meter was originally based on the shape of the earth as well - the distance from the pole to the equator was defined as 10 Mm in 1793. As far as the US unit tragedy goes, I think it's important to remember that SI units are full of compromises in exactly the same way that US units are, because they need to accommodate practical, human scale concerns. For example, degrees Celsius is a ridiculous concept from a scientific point of view (ask any beginning chemistry student who just messed up their test because they forgot to convert to Celsius to Kelvin before applying PV=nRT). If you believe the point of a unit system is to be useful for science, it's hard to defend a unit where 0 doesn't actually mean 0, since it introduces all sorts of confusion in the same way as traditional units do. And why does the whole world still measure days with 24 hours in them, each with 60 minutes, each with 60 seconds? Because decimal time (although France tried to impose it during the transition to SI units) is just too darn inconvenient for humans to use. The failure of decimal time shows why humans prefer non-decimal units: because the resulting units are human-scale. Converting from seconds to hours or days is not as easy as multiplying by 1000, but kiloseconds is an inconvenient unit - too short for an hour, while 100 kiloseconds is significantly longer than a day. Somehow the metric world manages these conversions just fine (in the same way the US manages conversions between inches, feet and yards). The traditional units evolved over hundreds of years, and I'm glad the US keeps them around - like nautical miles, they are quite useful.