3 ms·

"The head adds six to eight kilograms of weight, but by tilting the head forward it increases to something like twenty kilograms" Astonishing. My head's mass (

by scubbo 6y ago

"The head adds six to eight kilograms of weight, but by tilting the head forward it increases to something like twenty kilograms" Astonishing. My head's mass (or is it weight?) can be increased simply by moving it slightly it? Someone alert the physicists!

gonzo 6y ago
> Someone alert the physicists! Physicists already know about relativistic mass. /s
hnick 6y ago
Mass is static [in this context], but weight is a force and will apply differently based on angles. I'm no physicist but they might have got it right here.
- pjscott 6y ago
  Weight doesn't vary like that. What varies based on angle are the counterbalancing forces applied by your various body parts to keep it in place. That's vaguely similar to what the article said, so they may be basing this on an original claim that isn't nonsensical -- but if so it got badly garbled.
  - hnick 6y ago
    Well we all know holding you arm straight up or holding it out perpendicular to your body for 30 seconds are very different in terms of effort, perceived force, and pain. I think that's what they were going for.
    - KMag 6y ago
      Okay, but where did they get 20 kg / 200 Newtons / 44bs? I can see the assertion that there's zero transverse force across the neck when the head is held strait up, but how do they come up with a force greater than the weight of the head and neck? A.x cos(x) <= 1.0. Holding your neck out horizontally, the full weight of your head and neck is exerted transversely across your neck, but that's nowhere near 200 Newtons, and that's the worst case. Giving an exact figure implies they've done some calculation, and either their understanding of the physics is way off, or their arithmetic has gone far off the rails.
      - hnick 6y ago
        Someone who remembers their physics should probably reply with actual numbers but I think lever forces are what is at play. A downward force approximate to the mass of the head (6-8kg) is applied, the neck is a lever, and the force at the other end reacts appropriately. Wikipedia says: if the distance a from the fulcrum to where the input force is applied (point A) is greater than the distance b from fulcrum to where the output force is applied (point B), then the lever amplifies the input force. So that says that you can get a higher output force than the input force, which in this case is the force applied due to gravity and mass (plus your walking motion).
  - uoaei 6y ago
    AFAIK weight is the "effective" force due to gravity, meaning the force exerted to keep the mass stationary is the weight. If the mass is on the end of a lever, it will be heavier as it will require more force to keep it from falling toward the Earth.
    - pjscott 6y ago
      That definition sounds fairly non-standard. https://en.wikipedia.org/wiki/Weight#Definitions https://en.wikipedia.org/wiki/Weight#Definitions
m463 6y ago
Well, honestly weight is not mass. If you treat the neck as a pivot point it can require more or less force to maintain position of the head. https://en.wikipedia.org/wiki/Lever https://en.wikipedia.org/wiki/Lever
- Woberto 6y ago
  Right, it adds a moment, which is force times a distance. Which doesn't need to be explained to the average reader, but at least the article should say it puts more weight on the neck, or something like that.
  - necovek 6y ago
    While you are technically correct, I can't imagine you challenging anyone about their weight (in kgs/lbs) when they step on a scale because the scale might not be calibrated to the "force of gravity" (which is itself not a force) at the spot of measurement. So since it, as you nicely put it, does not need to be explained to the average reader, the complaint sounds like needless nitpicking. Even "more weight in the neck" is imperfect — weight usually means mass, so "load", implying force, is better. Thus I think it's acceptable to use the original wording to avoid all the technicalities that require a few parapgraphs to explain :)

by scubbo 6y ago

gonzo 6y ago

> Someone alert the physicists! Physicists already know about relativistic mass. /s

hnick 6y ago

Mass is static [in this context], but weight is a force and will apply differently based on angles. I'm no physicist but they might have got it right here.

pjscott 6y ago
Weight doesn't vary like that. What varies based on angle are the counterbalancing forces applied by your various body parts to keep it in place. That's vaguely similar to what the article said, so they may be basing this on an original claim that isn't nonsensical -- but if so it got badly garbled.
- hnick 6y ago
  Well we all know holding you arm straight up or holding it out perpendicular to your body for 30 seconds are very different in terms of effort, perceived force, and pain. I think that's what they were going for.
  - KMag 6y ago
    Okay, but where did they get 20 kg / 200 Newtons / 44bs? I can see the assertion that there's zero transverse force across the neck when the head is held strait up, but how do they come up with a force greater than the weight of the head and neck? A.x cos(x) <= 1.0. Holding your neck out horizontally, the full weight of your head and neck is exerted transversely across your neck, but that's nowhere near 200 Newtons, and that's the worst case. Giving an exact figure implies they've done some calculation, and either their understanding of the physics is way off, or their arithmetic has gone far off the rails.
    - hnick 6y ago
      Someone who remembers their physics should probably reply with actual numbers but I think lever forces are what is at play. A downward force approximate to the mass of the head (6-8kg) is applied, the neck is a lever, and the force at the other end reacts appropriately. Wikipedia says: if the distance a from the fulcrum to where the input force is applied (point A) is greater than the distance b from fulcrum to where the output force is applied (point B), then the lever amplifies the input force. So that says that you can get a higher output force than the input force, which in this case is the force applied due to gravity and mass (plus your walking motion).
- uoaei 6y ago
  AFAIK weight is the "effective" force due to gravity, meaning the force exerted to keep the mass stationary is the weight. If the mass is on the end of a lever, it will be heavier as it will require more force to keep it from falling toward the Earth.
  - pjscott 6y ago
    That definition sounds fairly non-standard. https://en.wikipedia.org/wiki/Weight#Definitions https://en.wikipedia.org/wiki/Weight#Definitions

m463 6y ago

Well, honestly weight is not mass. If you treat the neck as a pivot point it can require more or less force to maintain position of the head. https://en.wikipedia.org/wiki/Lever https://en.wikipedia.org/wiki/Lever

Woberto 6y ago
Right, it adds a moment, which is force times a distance. Which doesn't need to be explained to the average reader, but at least the article should say it puts more weight on the neck, or something like that.
- necovek 6y ago
  While you are technically correct, I can't imagine you challenging anyone about their weight (in kgs/lbs) when they step on a scale because the scale might not be calibrated to the "force of gravity" (which is itself not a force) at the spot of measurement. So since it, as you nicely put it, does not need to be explained to the average reader, the complaint sounds like needless nitpicking. Even "more weight in the neck" is imperfect — weight usually means mass, so "load", implying force, is better. Thus I think it's acceptable to use the original wording to avoid all the technicalities that require a few parapgraphs to explain :)