6 ms·

The thing is, though, that you have these conversions even within the imperial system (https://en.m.wikipedia.org/wiki/Imperial_units#/media/File%3AEnglish_Leng

The thing is, though, that you have these conversions even within the imperial system (https://en.m.wikipedia.org/wiki/Imperial_units#/media/File%3AEnglish_Length_Units_Graph.svg https://en.m.wikipedia.org/wiki/Imperial_units#/media/File%3...) but not within the metric system. My experience with U.S. students is that they are having a much harder time making sense of the imperial system (that they are used to) than doing problems in metric, even though they don’t use it in everyday life.

mulmen 6y ago
Ok, so? First off, you linked to a list of english measures which are not used in the US. Nobody uses fathoms or barleycorns. Here is the list of actual US customary units: https://en.m.wikipedia.org/wiki/United_States_customary_units https://en.m.wikipedia.org/wiki/United_States_customary_unit... Second, none of that is relevant to landing on Mars. The only problem space where metric has an advantage is in converting between meters, kilometers and millimeters. That’s great, and it’s easy to learn. But it doesn’t suddenly make all problems of distance easier to solve. If I am traveling toward Mars at 47 meters per second it doesn’t help me to know that is also .047km per second. And converting to kilometers per hour involves using base 60 twice anyway because metric time is unwieldy. In reality none of your measurements are going to be nice round numbers. Mentally converting from meters to km might be nice sometimes but it’s essentially a party trick. It won’t help the lander make decisions. The hardware doesn’t inherently work in base 10. Does NASA mix meters and kilometers? Isn’t that the same problem that destroyed the Mars Climate Orbiter? The fact is the units are irrelevant beyond just being defined and used consistently. Also, I can’t think of a situation where I need to convert miles to feet. My bike ride is six miles, I’m never going to express that in feet. If I need to describe the size of a thing in a room I will probably use feet, maybe inches if it is small. Probably not feet and inches. I wouldn’t use miles at all. Easy conversion between those units just isn’t a problem that comes up. It’s more important to me to have reasonably sized units and that the person I am communicating with understands them.
- lmm 6y ago
  > If I am traveling toward Mars at 47 meters per second it doesn’t help me to know that is also .047km per second. Yes it does. It means you can immediately sanity-check your numbers even if you don't have a good sense of what meters and kilometers are, because you have that base/kilo relationship. > My bike ride is six miles, I’m never going to express that in feet. You can eyeball how fast you're going in feet per second and have a rough idea of how long your ride is going to take. Or rather you could if you had any idea of how long your ride was in feet. There are lots of little everyday things that just become much easier.
  - mulmen 6y ago
    I’m not sure how that sanity check works, can you explain? Do you mean checking conversion between meters and kilometers? Because sure, that’s easier but you could just do everything in meters instead and not run the risk of crashing a spacecraft because of unnecessary conversions or bad assumptions. I estimate my bike ride progress in landmarks and time. Not feet per second. Did I get to the boat ramp in 20minutes? Better speed up and get to the park by 30.
    - lmm 6y ago
      > Do you mean checking conversion between meters and kilometers? Because sure, that’s easier but you could just do everything in meters instead and not run the risk of crashing a spacecraft because of unnecessary conversions or bad assumptions. But you'll have small distances and large distances and pieces from external sources who use measurements on a scale that makes sense to them. You can make your external sources do conversions themselves, but that's just moving the problem around. There will usually end up being a point, or probably several points, where you have to relate a small distance to a large distance, and wherever that happens, a human sanity check is a help. > I estimate my bike ride progress in landmarks and time. Not feet per second. Did I get to the boat ramp in 20minutes? Better speed up and get to the park by 30. Precisely - you have no sense of the relation between your speed and how far you can go, because you're using a terrible measurement system, and you don't even notice the how that's robbing you of the ability to develop useful intuitions.

mulmen 6y ago

Ok, so? First off, you linked to a list of english measures which are not used in the US. Nobody uses fathoms or barleycorns. Here is the list of actual US customary units: https://en.m.wikipedia.org/wiki/United_States_customary_units https://en.m.wikipedia.org/wiki/United_States_customary_unit... Second, none of that is relevant to landing on Mars. The only problem space where metric has an advantage is in converting between meters, kilometers and millimeters. That’s great, and it’s easy to learn. But it doesn’t suddenly make all problems of distance easier to solve. If I am traveling toward Mars at 47 meters per second it doesn’t help me to know that is also .047km per second. And converting to kilometers per hour involves using base 60 twice anyway because metric time is unwieldy. In reality none of your measurements are going to be nice round numbers. Mentally converting from meters to km might be nice sometimes but it’s essentially a party trick. It won’t help the lander make decisions. The hardware doesn’t inherently work in base 10. Does NASA mix meters and kilometers? Isn’t that the same problem that destroyed the Mars Climate Orbiter? The fact is the units are irrelevant beyond just being defined and used consistently. Also, I can’t think of a situation where I need to convert miles to feet. My bike ride is six miles, I’m never going to express that in feet. If I need to describe the size of a thing in a room I will probably use feet, maybe inches if it is small. Probably not feet and inches. I wouldn’t use miles at all. Easy conversion between those units just isn’t a problem that comes up. It’s more important to me to have reasonably sized units and that the person I am communicating with understands them.

lmm 6y ago
> If I am traveling toward Mars at 47 meters per second it doesn’t help me to know that is also .047km per second. Yes it does. It means you can immediately sanity-check your numbers even if you don't have a good sense of what meters and kilometers are, because you have that base/kilo relationship. > My bike ride is six miles, I’m never going to express that in feet. You can eyeball how fast you're going in feet per second and have a rough idea of how long your ride is going to take. Or rather you could if you had any idea of how long your ride was in feet. There are lots of little everyday things that just become much easier.
- mulmen 6y ago
  I’m not sure how that sanity check works, can you explain? Do you mean checking conversion between meters and kilometers? Because sure, that’s easier but you could just do everything in meters instead and not run the risk of crashing a spacecraft because of unnecessary conversions or bad assumptions. I estimate my bike ride progress in landmarks and time. Not feet per second. Did I get to the boat ramp in 20minutes? Better speed up and get to the park by 30.
  - lmm 6y ago
    > Do you mean checking conversion between meters and kilometers? Because sure, that’s easier but you could just do everything in meters instead and not run the risk of crashing a spacecraft because of unnecessary conversions or bad assumptions. But you'll have small distances and large distances and pieces from external sources who use measurements on a scale that makes sense to them. You can make your external sources do conversions themselves, but that's just moving the problem around. There will usually end up being a point, or probably several points, where you have to relate a small distance to a large distance, and wherever that happens, a human sanity check is a help. > I estimate my bike ride progress in landmarks and time. Not feet per second. Did I get to the boat ramp in 20minutes? Better speed up and get to the park by 30. Precisely - you have no sense of the relation between your speed and how far you can go, because you're using a terrible measurement system, and you don't even notice the how that's robbing you of the ability to develop useful intuitions.