# A question regarding columns and GNm and MNm

1. Jun 3, 2012

### Harrison01

Ok i have a question regarding columns and it goes a bit like this,

What is the minimum length of the column at which buckling is
likely to occur?

They have given me the youngs modulus of 200GNm-2 (200,000,000,000 Nm) and a yield stress of 140MNm-2 (140,000,000Nm).

For working out my equation i'm trying to get the figures in the same unit. So 200GNm-2 to MNm

Do i divide the 200 by 1 million to give me 0.0002Nm and then multiply it by 100,000 to give me 200, but this then cant be right?

where am i going wrong folks....

2. Jun 3, 2012

### nvn

Harrison01: (1) MN*m^-2 is called MPa. Always use the correct, special name for a unit. E.g., 140 MPa, not 140 MN*m^-2. See the international standard for writing units (ISO 31-0).

(2) Always leave a space between a numeric value and its following unit symbol. E.g., 140 MPa, not 140MPa.

(3) Two unit symbols multiplied together cannot be written together, and must be separated by an asterisk or a space. E.g., N*m or N m, not Nm.

(4) The international standard says you can write digits of long numbers in groups of three, separated by spaces, not commas. E.g., 140 000 000 Pa, not 140,000,000 Pa.

(5) 1 GPa = 1000 MPa. Therefore, 200 GPa = 200 000 MPa.

(6) Other valid ways to write 200 000 MPa include, e.g., 200*10^3 MPa, or 200e3 MPa. Another way to write, e.g., -0.3 m^-4 is -0.3*10^-12 mm^-4, or -0.3e-12 mm^-4.

Last edited: Jun 3, 2012
3. Jun 4, 2012

### Harrison01

Cheers NVN, thats starting to make things alot clearer for me now...

I think what threw me is that in the question i was given, all the figures were GN m and MN m and the example i was given the figures were in MPa and GPa..

Finding getting used to all these SI units and powers of 10 a struggle as its been so long since last using it..