## Materials Science C

raxu
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### Re: Materials Science C

In the sonic powerpoint there are a few formulas for weight distribution I don't quite understand...

Number Average $\overline{M_n}=\frac{\sum N_iM_i}{\sum N_i}$ ,
Weighted average = $\overline{M_w}=\frac{\sum N_iM_i^2}{\sum N_iM_i}$ ,
Molecular weight average $\overline{M_z}=\frac{\sum N_iM_i^\alpha}{\sum N_iM_i^{\alpha-1}}$ .

Can someone explain what they are for?
Richard A. Xu
Events involved 17/18: Astro, Chem, Fermi, Game, Mat Sci, Optics, Thermo.

sonred
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### Re: Materials Science C

raxu wrote:In the sonic powerpoint there are a few formulas for weight distribution I don't quite understand...

Number Average $\overline{M_n}=\frac{\sum N_iM_i}{\sum N_i}$ ,
Weighted average = $\overline{M_w}=\frac{\sum N_iM_i^2}{\sum N_iM_i}$ ,
Molecular weight average $\overline{M_z}=\frac{\sum N_iM_i^\alpha}{\sum N_iM_i^{\alpha-1}}$ .

Can someone explain what they are for?

number average is doesn't take into account that heavier molecules contribute more to the molecular weight than lighter molecules where as weighted average does.

sonred
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Posts: 3
Joined: Tue Jan 09, 2018 10:15 pm
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### Re: Materials Science C

raxu wrote:In the sonic powerpoint there are a few formulas for weight distribution I don't quite understand...

Number Average $\overline{M_n}=\frac{\sum N_iM_i}{\sum N_i}$ ,
Weighted average = $\overline{M_w}=\frac{\sum N_iM_i^2}{\sum N_iM_i}$ ,
Molecular weight average $\overline{M_z}=\frac{\sum N_iM_i^\alpha}{\sum N_iM_i^{\alpha-1}}$ .

Can someone explain what they are for?

number average is doesn't take into account that heavier molecules contribute more to the molecular weight than lighter molecules where as weighted average does.