unit for force always N?

[alexzive]

Hello,

if my basic units are different from kg,m,s, am I still allowed to use N (Newton = 1 Kg*m/s²) for forces (loads) ?
or should I adjust the unit for my forces accordingly (i.e. g*mm/s²) ?

many thanks, Alex

 

[bassmanjax]

Yes, you can use Newtons for force as it is one of the basic units, along with length and time. You just have to remember that your derived quantities will reflect whatever force unit you use;

i.e. Force in N, length in mm = Stress in N/mm^2
Force in kN, length in mm = Stress in kN/mm^2

Regards

Martin

Martin Stokes CEng MIMechE

 

[bassmanjax]

^^ Correction ^^

..assuming that you are using SI units of course

Martin Stokes CEng MIMechE

 

[alexzive]

actually I am doing Thermo-Mechanical Coupling, so my basic units are g,mm,s,°C. I would prefer to avoid using Newton,
because I have thermal prop. like thermal conductivity in J/(s*mm*C) and density in g/mm³.
So my forces should be expressed then in g*mm/s² which corresponds to 10^6 N!!!

In the Abaqus docum. Newtons come up with E modulus and mechanical loads.

my question: can I use g*mm/s² (which is coherent with my basic units) instead of N, everywhere in my simulation? (of course then I would have stress in g/(s²*mm) )

Many Thanks, Alex

 

[alexzive]

*errata:

g*mm/s² which corresponds to 10^-6 N

 

[corus]

I prefer to use newtons, kgs, mm and Watts consistently rather than get muddled up by mixing units. I've seen too many mistakes before where people are unable to convert millimatres to metres, and for some reason mix imperial units with metric. The result is that your spaceship ends up colliding into Mars, if I remember correctly. In addition your stresses will be in values of tens or hudnreds, which I've found to be more meaningful to people than saying the stress is 'x' times 10 to the power 11 Giggly Pascals, or whatever they are.

corus

 

[bassmanjax]

You can use any units you want, as long as they are logical and consistent. I'm not sure how feasible it would be to express stress in g/(s²*mm) - a lot of people would be mislead or confused by that as a unit choice.

Regards

Martin Stokes CEng MIMechE