# OT: Speed of light

Jeff Schwab jeff at schwabcenter.com
Wed Feb 13 19:35:59 CET 2008

```Hrvoje Niksic wrote:
> Jeff Schwab <jeff at schwabcenter.com> writes:
>
>> Jeroen Ruigrok van der Werven wrote:
>>> -On [20080212 22:15], Dotan Cohen (dotancohen at gmail.com) wrote:
>>>> Note that Google will give a calculator result for "1 kilogram in
>>>> pounds", but not for "1 kilogram in inches". I wonder why not? After
>>>> all, both are conversions of incompatible measurements, ie, they
>>>> measure different things.
>>> Eh? Last I checked both pound and kilogram are units of mass, so where is
>>> the incompatibility?
>> I've never heard of "pound" as a unit of mass.  At least where I went
>> to school (Boston, MA), "pound" is the English unit of force, "slug"
>> is the (rarely used) English unit of mass, and "kilogram" is the SI
>> unit of mass.
>
> It would be possible for US pound to only refer to weight, but I
> cannot find references to corroborate it.  For example, taken from
> Wikipedia:
>
>     In 1958 the United States and countries of the Commonwealth of
>     Nations agreed upon common definitions for the pound and the
>     yard. The international avoirdupois pound was defined as exactly
>     453.59237 grams.
>
> The "pound-force" wikipedia entry documents "pound" being used as a
> unit of force "in some contexts, such as structural engineering
> applications."

That's suprising (to me, anyway.  We (Americans) all measure our weight
in pounds.  People talk about how much less they would weigh on the
moon, in pounds, or even near the equator (where the Earth's radius is
slightly higher).  I remember converting pounds to Newtons, and vice
versa, in school.  Apparently, what everybody here calls a "pound,"
Wikipedia lists as a "pound-force."  But I've only ever heard it called
a pound, if anybody ever used "pound" as a unit of mass at school,
they'd have been laughed at.

http://en.wikipedia.org/wiki/Pound-force

```