## Materials Science C

raxu
Exalted Member
Posts: 41
Joined: October 9th, 2014, 6:54 pm
Division: C
State: NY
Has thanked: 0
Been thanked: 0

### 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
Events done Div. B: Simple Machines , Shock Value.
Events done Div. C: Astronomy , It's About Time, Forensics, Optics, Remote Sensing, Game On, Materials Science, Mousetrap Vehicle, Fermi Questions, Thermodynamics.

sonred
Member
Posts: 3
Joined: January 9th, 2018, 2:15 pm
Has thanked: 0
Been thanked: 0

### 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
Member
Posts: 3
Joined: January 9th, 2018, 2:15 pm
Has thanked: 0
Been thanked: 0

### 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.

greekyogurt
Member
Posts: 1
Joined: January 22nd, 2018, 4:01 pm
Has thanked: 0
Been thanked: 0

### Re: Materials Science C

Hello! I just started a team this year, and was wondering what would be an example of a cheap+fairly easy practice lab for materials science? Additionally, is roughly 40 questions an unreasonable amount for the given time? (we looked at the practice tests on the wikia, but were hoping for something more recent)
thanks!

Unome
Moderator
Posts: 4250
Joined: January 26th, 2014, 12:48 pm
State: GA
Location: somewhere in the sciolyverse
Has thanked: 60 times
Been thanked: 29 times

### Re: Materials Science C

greekyogurt wrote:Hello! I just started a team this year, and was wondering what would be an example of a cheap+fairly easy practice lab for materials science? Additionally, is roughly 40 questions an unreasonable amount for the given time? (we looked at the practice tests on the wikia, but were hoping for something more recent)
thanks!
It sounds like you're trying to write a test?
Userpage
Chattahoochee High School Class of 2018
Georgia Tech Class of 2022

Opinions expressed on this site are not official; the only place for official rules changes and FAQs is soinc.org.

Concord
Member
Posts: 7
Joined: October 2nd, 2017, 10:46 am
Division: C
State: TX
Has thanked: 0
Been thanked: 0

### Re: Materials Science C

greekyogurt wrote:Hello! I just started a team this year, and was wondering what would be an example of a cheap+fairly easy practice lab for materials science? Additionally, is roughly 40 questions an unreasonable amount for the given time? (we looked at the practice tests on the wikia, but were hoping for something more recent)
thanks!
40 questions definitely isn't an unreasonable amount of questions on a test, but it may depend on the formatting of the questions. I.e. 40 essay/short answer questions may be too much, but something like 30 M/C, 5 Matching, and then 5 SAR would be a perfectly fine formatting. Additionally, the difficulty of the questions may factor in as well. If you want me to take a look at a potential test, just PM me and I would definitely be willing to give you feedback on it! Additionally, I can send you one or two previous invite tests for matsci, which should be more recent than the ones on the test exchange if you are willing!

Additionally, there are many good examples of easier practice labs. For example, using polymer specimens (i.e. ones used in forensics), you can determine which polymers (PVC,PET,LDPE,etc) are which based on sink/float testing in liquids of varying densities. Additionally, various Young's modulus labs involving rubber bands or trash bags may work as well.
William P. Clements '20

jaah5211
Member
Posts: 57
Joined: October 22nd, 2017, 7:42 pm
Division: C
State: FL
Has thanked: 0
Been thanked: 0
Contact:

### Re: Materials Science C

I had a question for the material science organic nomenclature naming. Would they ask the IUPAC (Systematic) naming or the common naming for the test?
2019 - 2020
Chemistry Lab, Protein Modeling, Forensics.

Concord
Member
Posts: 7
Joined: October 2nd, 2017, 10:46 am
Division: C
State: TX
Has thanked: 0
Been thanked: 0

### Re: Materials Science C

jaah5211 wrote:I had a question for the material science organic nomenclature naming. Would they ask the IUPAC (Systematic) naming or the common naming for the test?
I've seen tests with both questions about IUPAC naming as well as common naming, and there are also some tests that offer bonus points on nomenclature sections if you can provide both, i.e. UT Invitational 2017.
William P. Clements '20

Skink
Exalted Member
Posts: 947
Joined: February 8th, 2009, 12:23 pm
Division: C
State: IL
Has thanked: 0
Been thanked: 0

### Re: Materials Science C

Re: length, 40 MC is super short unless it's a small Regional. It's a fifty minute event, and MC (unless very well-written, which they usually aren't) don't take that long. A rule of thumb is that you want twice the number of questions as teams in attendance at minimum, but I'd have more questions, yet, if they're MC.

Re: nomenclature, know the IUPAC rules in and out, but know commonplace common names. I've found even higher-end teams using systematic names that no chemist would seriously use when given the freedom to choose any acceptable name.

Raleway
Exalted Member
Posts: 228
Joined: March 12th, 2017, 7:19 pm
Division: C
Has thanked: 0
Been thanked: 0

### Re: Materials Science C

Adding on to Skink, most tests are designed to either have teams just barely finish or not finish to separate top end teams. Some tests can range from 60 MC, Lab, 30 nomenclature, and 10 SAQ to some that are just 5 really long open-ended with a lab. It is in your best interest especially for your own team to make a test that they cannot finish as it forces them to really assess how long they spend on each question.

Regarding IUPAC vs Industry, just know both. No self-respecting scientist says ethanoic acid as a common way to refer to acetic acid. A very common mistake many make is to use the common name "isopropyl." Many times, using "isopropyl" will change the main chain number of alcohols and thus completely screw up IUPAC naming. No one will say IUPAC is wrong; some may say industry names are wrong. When in doubt (or not specifically stated), use IUPAC.
Sleep is for the week; one only needs it once a week

God bless Len Joeris | Balsaman

### Who is online

Users browsing this forum: No registered users and 1 guest