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Simply Harmonic Jello – Fun Physics for Thanksgiving November 23, 2010

Posted by admin in : Acoustics (ACOU), Condensed Matter and Materials Physics (CMMP), History, Policy and Education (HPE), Physics Education Research (PER) , add a comment

Jello is fun and delicious any time of year, and everyone has seen it “wiggling” and “jiggling”.  With a simple stopwatch and counting the frequency of the wiggles, serving jello brings up a special opportunity to work a physics experiment into your snack and dinner menu.

Those wiggles and jiggles can be described as simple harmonic motion, i.e., the force causing the displacement (motion) is proportional to the displacement itself,  F = -kx .

Consider a square block of wiggling jello on a flat plate.  If the jello is set into vibrating motion by a shear force that acts on the top of the jello, static friction will keep the bottom of the jello fixed in place on the plate.   The displacement (or deformation) of the top of the jello due to the shear force is some distance,  x . This displacement divided by the original dimension is called the shear strain.

From Giancoli, Physics for Scientists and Engineers

If you measure the wiggling rate, i.e., count the number of back and forth excursions per unit time, this frequency can be related to the a physical property of the jello called the shear modulus.

The shear modulus,  G relates the shear force,  F , and shear strain,  \frac{x}{h}   by  

 G = \frac{Fh}{Ax}    or F = \frac{GAx}{h}

where   A is the area of the top of the block.

Because the center of mass oscillates with half the displacement of the top,

 F=\frac{1}{2} k_e x ,

and the effective force constant is given by

 k_{e} = 2\frac{ F}{x} = \frac{2GA}{h} .

The frequency of the vibrations for any simple harmonic oscillator is

 f =\frac{1}{2 \pi} \sqrt{\frac{k_e}{m}}

where  m is the  mass oscillating object, in this case the piece of jello.  The piece of jello can be weighed directly (converting from weight to mass) or given by the density of the jello multiplied by its volume  m= \rho Ah .

So the wiggling frequency of jello is        \frac{1}{2 \pi}  \sqrt{\frac{\frac{2GA}{h}}{\rho Ah}} or  \frac{1}{2 \pi h}{\sqrt{ \frac{2G}{\rho}} .

Thus the shear modulus of jello can be determined from the measured vibrational frequency by  G= 2 \rho ( \pi  f h)^2  .

You can try this experiment at home and even study how the shear modulus changes with how you make the jello, i.e., with water, vinegar, juice, soda, or alcohol. And you can investigate how temperature changes the shear modulus.

Post your results here as a comment.   Check back for updates and useful data.


Units? When doing any calculation in science it is important to keep in mind the units of the factors in used in the equations.  The units have to be consistent throughout, and the final derived units of your calculation should be consistent with quantity that you are trying to calculate.  It is easy to mix up units if you make length measurements using English units, and mass measurements in the metric system for example.   Even when using the metric system throughout, one could easily make the mistake of mixing CGS units with MKS units.  Always check your units.

The density of jello? Understanding what jello is and how it is made is an interesting lesson in biochemistry, particularly protein structure and function.

The more general name for jello is gelatin.  (Jell-0 is a brand name for the foodstuff – edible gelatin – that has become synonymous with the food itself.) Gelatin is made from the connective tissue proteins of cows or pigs. It is made first by breaking down the cellular structure of the connective tissues.  Then collagen proteins from these tissues are isolated, denatured and subsequently rendered to a powdered form.  Sweeteners, flavoring agents, dyes and other additives are added to this powder to make the familiar gelatin dessert.  To make jello you have to add boiling water to the powder which dis-aggregates the proteins.   Cooling the mixture re-aggregates the proteins.   The final jello mold will be a complex solid mixture of proteins, water, air, and chemical additives.

This leads us to consider the density of jello, which like the biological tissue from which it comes, is mostly water.

Water’s density is  1 \frac{g}{cm^3} = 1000 \frac{kg}{m^3} .  So the density has to be close to water.  But the various additives result in partial molar volumes that contract or expand the total volume.   The final volume depends on the thermodynamic nature of the additives and their relative concentrations.  So while it is easy to think that in any given volume of jello there are constituents that are heavier than water, and that the density should be greater than  1 g/cm^3 , the complex mixture of additives could result in the overall density being less than  1 g/cm^3 .  The most prudent thing to do is to take a well measured cube of jello, calculate its volume (or use volume displacement), weigh it, then calculate its density.

Reported densities for  jello have ranged from  0.98 - 1.3 g/cm^3 (with sugar-free variants being on the low end), while for scientific gelatin (without all the food additives) the density has been reported to be  1.3 g/cm^3 .

Life in the Margins November 19, 2010

Posted by ASTRO Section Chair in : Astronomy and Astrophysics (ASTRO), History, Policy and Education (HPE) , add a comment

by Dr. Jarita C. Holbrook

This week I have been writing my annual report to the National Science Foundation on the Astronomy Networks project.  Since I moved into cultural astronomy, I have lived the life of an interdisciplinary scholar in the margins.  My behavior and choices are consistent with the research findings I discussed last week: women and minorities tend to find success at the margins of STEM disciplines rather than in the mainstream.  Life in the margins is not bad: I exercise my intellectual freedom, I have a positive international research reputation, and I have been attracting great students.  When I moved into cultural astronomy from the way other academics responded to me (somewhat condescendingly), I determined that I had to get external funding to be taken seriously.  Simply put, it is fine to do interesting research in unestablished areas between disciplinary boundaries, but getting external funding is the official seal of approval.  Many scholars have had the good fortune of having their place in the margins be moved to the center, for example Jeff Marcy and his planet finding projects.

I am co-PI with Sharon Traweek (UCLA) on an NSF funded project that studies women and minority astronomers and their professional networks.  We are studying how they get involved in big database driven astronomy projects that are mainstream and where they chose to make a contribution.  Are they central or on the margins? Where do they perceive themselves to be and do others agree?

For my part of the project, I have been focusing on the Large Synoptic Survey Telescope (www.lsst.org).  The LSST has not been built.  It is estimated to be completed in 2012.  LSST when it is finished will break all the rules of big telescope construction, management, computing, and collaboration.  There will be no proprietary data, that is anyone and everyone can access the data soon after the observations.  Of course, having an internet connection and enough memory to handle the large images are necessary.

I have been involved in the International Astronomical Union’s new Astronomy for Development initiative.  Projects such as LSST will present a great opportunity for astrophysicists outside of Europe and North America to work with the best data available.  The catch is that they have to learn how to work with LSST data now, in order to be ready when the real data starts flowing.  International scientists need to get networked into LSST now! The LSST team has created a simulator that can be used to simulate what the data will look like.  The simulated data can be used to test if certain astrophysical questions are feasible given the physical parameters of the LSST and the data it will produce.  As with all aspects of the LSST project, the simulator is freely available.  LSST is the type of project that I can admire.

I’m involved in the formation of the African Astronomical Society.  At the upcoming IAU Symposium “Tracing the Ancestry of Galaxies – on the Land of our Ancestors” in Ougadougou, Burkina Faso, this December, the first meeting of the working group will take place.  I secretly hope that they will go ahead and announce the formation of the Society there.  If not an official announcement will take place at MEARIM2 – the second Middle-East and Africa Regional IAU Meeting in South Africa in April 2011.  The newly formed Society should work to make sure that African astrophysicists get involved in LSST.  Unfortunately, because I am in India I will not go to Burkina Faso.

The Astronomer Networks project is also an oral history project, so our interviews are tape recorded and will be edited for an online archive.  I have interviewed a dozen astronomers thus far, but this is far too few to draw any grand conclusions.  The graduate students and postdocs on the project have collectively interviewed a dozen more, still not enough data.  However, we are on our way and have discovered some interesting results that may change as we collect more interviews.  What I find most significant about the oral history part of the project is that most oral histories of astronomers focus on the old and famous.  Few include the young and becoming astronomers at a stage in their careers where they have committed to being part of a project that may or may not be spectacular.  Even fewer include self-identified minority astronomers, though many include a smattering of women.

In a reflexive loop, I am in the disciplinary margins studying astronomers in the margins after having been an astronomer not so in the margins.

I’m now in Bangalore, India, visiting the Raman Research Institute (www.rri.res.in).  Next week begins a ten day festival focused on astronomy at the local planetarium.  I plan to write an article about the festival for one of the popular astronomy magazines.

NSBP and SAIP Members on LHC Lead-Lead Collisions November 16, 2010

Posted by ASTRO Section Chair in : Astronomy and Astrophysics (ASTRO), Cosmology, Gravitation, and Relativity (CGR), Mathematical and Computational Physics (MCP) , 2comments

LHC Achieves Heavy Ion Collisions
On Sunday November 7 at 1 am local time the first heavy ion collisions were observed in the Large Hadron Collider (LHC) near Geneva, Switzerland.  By the following Monday morning the heavy ion beam was stably producing a steady stream of collisions such that the physics analysis could start in earnest.  By the end of the week a sufficient number of events had been observed to reach the first conclusions.

Witnessing this historic event was Dr. Zinhle Buthelezi from South Africa’s iThemba LABS who was on duty in the control room of the ALICE (A Large Ion Collider Experiment) detector at the time of the first collisions.  Other members of the iThemba LABS team, Deon Steyn, Siegie Foertsch, and Zeblon Vilakazi, as well as the team from the University of Cape Town led by Jean Cleymans have also been participating in the ALICE experiment.  More

ALICE, Quark-Gluon Plasmas and the Origin of the Universe
The goal of ALICE is to observe the so-called Quark Gluon Plasma (QGP).  This plasma is partially analogous to the more well-known electronic plasma that results when a gas is so hot that its electrons are liberated from their atomic nuclei.  Like electrons are constituents of atoms, quarks and gluons are constituents of nucleons – protons and neutrons.  They can likewise be “deconfined” from nucleons at high energy densities like those that existed at the very moment of the Big Bang, or can be reproduced in high energy accelerators like the Relativistic Heavy Ion Collider (RHIC) or the LHC.  Thus the results gained from ALICE and RHIC give insights into the state of energy and matter in the first microseconds of the universe, before condensation into neutrons, protons, and subsequently atoms.   More

NSBP Members Clifford Johnson and Stephon Alexander on the ALICE collisions
Experimental Excitement
ALICE – A Cosmologist’s Point of View

Theoretical physicists have studied QGPs using a variety of techniques.  Perhaps the most successful method is due to Dr. Juan Maldacena, a plenary speaker at the 2005 Joint Annual Conference of the National Society of Black Physicists and the National Society of Hispanic Physicists.  The so-called “AdS/CFT correspondence” relates string theory to gauge theories like quantum chromodynamics (QCD) which describes the interactions between quarks and gluons. Professor Jim Gates has commented, “So, the next time someone tells you that string theory is not testable, remind them of the AdS/CFT connection…”  Since then experimental, observational, and theoretical evidence has expanded from particle theory to condensed matter physics.

South African Participation at CERN
In addition to the ALICE experiment, South African physicists are participates in the ATLAS experiment.  Dr. Simon Connell, President-elect of the South African Institute of Physics leads the ATLAS Team at the University of Johannesburg.  “ATLAS is designed to answer some of the most fundamental questions about the nature of the universe, like how and why particles have mass,” he explains.

This past summer South Africa hosted the first biennial African school on fundamental subatomic physics and its applications. More

2010 African Physics School

Courtesy of Brookhaven National Lab

South African participation in particle physics brings many benefits to the country and continent, most notably in information and computing technology (ICT).  SANReN, the grid computing network that allows physicists in South Africa to receive results from the LHC is used by many others in science and business, and this network will by design be extended to everyday consumers and learners.  More

ALICE, Quark-Gluon Plasmas and the Origin of the Universe – A Cosmologist’s Comment November 16, 2010

Posted by ASTRO Section Chair in : Astronomy and Astrophysics (ASTRO), Cosmology, Gravitation, and Relativity (CGR) , 1 comment so far

Currently the best modern framework for understanding the origin of large scale structure in our universe is called cosmic inflation.

While still not completely resolved, inflation predicts the observed features of the universe split seconds after the big bang and three hundred thousand years during another era where the universe was filled with another type of plasma-an ionized gas of baryons and photons.   However when inflation was first ignited (10-36 seconds), the universe was thought to be filled with pure vacuum energy, no particles and radiation.

One of the big mysteries in cosmology and fundamental physics is to understand precisely how inflation ended and dumped its energy into the form of radiation.  A curious hint is that at time 10-12 seconds the universe was filled only with the quark-gluon plasma.

A key mystery of cosmology and fundamental physics is to understand how the universe went from the inflating state to the quark-gluon plasma state.  By understanding this new state of matter, the quark gluon plasma, physicists can help us understand the physics of the early universe right at the LHC.

Likewise, string theorists are developing new tools within the framework of M/String-Theory called the Ads/CFT correspondence which gives new insights into the non-perturbative physics by relating the physics of charged black holes “holographically” to the quark-gluon plasma.  It is amusing to speculate on how this new understanding could impact the experiments at the LHC and any possible relation to the physics of cosmic inflation.

Stephon Alexander

Professional Self-Image and Astronomy November 12, 2010

Posted by ASTRO Section Chair in : Astronomy and Astrophysics (ASTRO), Cosmology, Gravitation, and Relativity (CGR), History, Policy and Education (HPE) , add a comment

by Dr. Jarita C. Holbrook

My cultural astronomy project on navigation focused on why people today continue to navigate on the ocean using celestial bodies. A glaring question was why are people not adopting the Global Positioning System (GPS). There are many factors, many that are obvious such as batteries, as to why the GPS is not used in all navigating communities. However, after doing various calculations and listening to what the navigators said, I identified a new factor which is professional self-image. The question became: How do the navigators in this community image themselves to be in terms of their skills, the way they act, their values, etc.? I was most interested in the skills aspect of this question.

For my navigation study, I focused on three communities; and their professional self-image was different in each of these. Each community had a set of navigation skills and abilities that they considered to be essential to being a navigator. For example, on the Kerkennah Islands in Tunisia, the fishermen need to have a mental map of the seafloor features around the Islands to be able to pinpoint their location. Translating the relative depth of water to a specific location was a skill that the fishermen were proud of being able to do.

After my five years of studying navigators, I proposed a new hypothesis:

There are skills and abilities that are an essential part of the professional self-image of navigators, when a new technology is positioned to replace that essential part there will be rejection and/or resistance before adoption if adoption occurs.

My study of the United States Naval Academy (USNA) revealed a case of resistance and struggle between celestial navigation and the GPS. It is even more interesting because the GPS was developed by the Navy! Among Navy Officers, all are required to take celestial navigation classes and get certified (get a badge/pin) in celestial navigation, marking it as an essential skill. When it was proposed to remove celestial navigation from the USNA curriculum, there was struggle and resistance. At the end of my study, it was still being taught at the Naval Academy but in a stripped down form. The GPS is used by the Navy but so is celestial navigation, one is used to test the accuracy of the other. However, it is the old fashioned celestial navigation that is used to check the GPS!

There are many efforts underway to diversity Science, Technology, Engineering, and Mathematics (STEM) disciplines. Many efforts have had little or limited success. I have been on the Gender Equity Conversation Task Force run by the American Physical Society (APS) this past year doing site visits to physics departments in the United States. In conjunction with my film “Hubble’s Diverse Universe” I have visited several astronomy departments as well, where the bulk of our post film discussion focused on diversifying astronomy. I am currently studying the National Astrophysics and Space Science Programme in South Africa, which is also meant to diversify astronomy. Not to forget that I too am a PhD astrophysicists and have done time in some of the best astronomy and physics departments in the USA. I had struggled with and continue to struggle with the professional self-image of astronomers. I have to mention that the French sociologist Pierre Bourdeau studied academic culture (Homo Academicus) and I could couch much of my thinking about the professional self-image of astronomers around his term “doxa”.

Focusing on diversity, I have been busily identifying those factors that are part of astronomers’ professional self-image that impede if not halt progress towards diversifying astronomy. As an aside, consider that women and minority scholars in the USA tend to create their own success at the margins of disciplines. One reason may be that the professional self-image within disciplines is inflexible (concrete, frozen, rigid) leading to no possibility of diversity and no chance of success for diverse members.

As an example of this within astronomy, in the discussions that followed viewing my film, in some cases the audience spent a great deal of time ‘othering’ minority students: they are only interested in money (read they come from poor backgrounds), they are more interested in less intellectual fields such as engineering (no offense, these were not my words!), and they would not want to make the time-investment necessary to become an astronomer. These comments were instructive to me on another level: I’ll not be sending my children nor my students to them, even my non-minority ones!

I have developed a series of activities to be done by students and astronomy professors around professional self-image to bring some of the factors hindering diversity to the forefront in an effort to identify and nullify unconscious biases. Thus far, I have done the student exercise twice in South Africa. It was fun and the students (who were black and colored South African) could see why they felt uncomfortable, unsupported, and abandoned by their professors. It gave them a morale boost building their resilience to survive in the astronomy environment. However, the students cannot change astronomy culture – the professors can. I hope to test out my professional self-image exercises sometime soon among astronomy professors.

This is my last week in South Africa. I traveled to Pretoria to see NSBP’s Charles McGruder, the International Astronomical Union President Robert Williams, and Astronaut and MIT Professor Jeff Hoffman give a joint public lecture to promote astronomy. Astronaut Hoffman helped fix the Hubble Space Telescope way back when the images were still out of focus. His presentation was moving, especially since I had done the “Hubble’s Diverse Universe” film which is a minority tribute to the Hubble Space Telescope. Afterward, I gave him a copy of my film – bold of me? Robert Williams I knew from my visits to the Space Telescope Institute; he was surprised to find me in South Africa. I was surprised that Charles had not told him that I would be there. Dr. Williams talked about some of the major findings of the Hubble Space Telescope advancing astronomy and astrophysics. Dr. Charles McGruder and I have a long history. He and I are both Caltech grads, except he graduated the year that I was born! I did not meet him until I was working on my master’s in astronomy. At the time it was wonderful to connect with an African American astronomer who also had survived undergraduate life at Caltech (in 2006 I met a third Dr. Alphose Sterling). Dr. McGruder spoke about the Square Kilometer Array (SKA) and what it would mean if it were placed in Africa. South Africa has put in a bid to host the SKA, and dishes would have to be placed in other African nations as well, which would bring astronomy to new places in Africa. Australia is competing with South Africa for the SKA.

Back in Mafikeng, Dr. Thebe Medupe and I are putting together a proposal to host the 2014 Oxford Conference on Archaeoastronomy in South Africa in Mafikeng. We got letters from each of the major hotels with quotes of their estimated room rates – two days of work! Our last task is to get a letter of support from North West University then I think we are ready to go. The proposal will be presented at the Peru conference in January. I am nervous about it because I will not be traveling to Peru, I will be in Seattle at the American Astronomical Society meeting (AAS). We have tossed around ideas for the theme of the conference. Our favorite thus far is: “Astronomy, Indigenous Knowledge, and Interpretation.”

Dr. Medupe and I have been planning the future of the Timbuktu science project and the Astronomy document collaborative project. Both focus on documents written in Arabic found in Africa that contain astronomy content. The Timbuktu project has been running for several years, I started building a larger collaboration last year starting with Egypt. Many African nations have archives of Arabic documents; these have not been analyzed for their astronomy content. The larger collaboration would identify those archives that have astronomy documents and then set up teams to analyze the documents. I am building the collaboration as a collaboration, not as me and a bunch of Americans going and doing everything. I want local partners who are willing to work as co-Investigators. It has been slow going because with each new partner we have to write joint grant proposals to get funding. It would certainly be a lot faster to simply send in a team, but I feel strongly that true partnerships will make the project sustainable and benefit more people including leading to training more local (African) students.

African Cultural Astronomy November 6, 2010

Posted by ASTRO Section Chair in : Astronomy and Astrophysics (ASTRO), History, Policy and Education (HPE) , add a comment

by Dr. Jarita C. Holbrook

It has finally started to rain in Mafikeng, South Africa. I was here teaching a class on African Indigenous Astronomy to undergraduate students at North West University. My host is Dr. R. Thebe Medupe who is the Chair of the Department of Physics and Electronics. The class included a series of assignments designed to explore Indigenous Astronomy, the tension between astronomy and indigenous astronomy, the geography of Africa, and astronomy. The final assignment was a constellation identification quiz. Using a green laser pointer, each student has to correctly identify ten things in the night sky. However, not all of my students have been able to arrange to be on campus at night to take the quiz. Now it is raining….Class management environments such as D2L and Moodle are great for automating quizzes, homework assignments, etc. The North West University equivalent is Efundi. I am thinking of using Stellarium and other star charts to design an online constellation identification exercise instead of the quiz. I spoke to two students about it, and they are in favor. I will start working on Friday morning.

Next year is the 6th Science Center World Conference that will take place in Cape Town, September 4 – 8, 2011. Two weeks ago Mike Simmons of Astronomers without Borders www.astronomerswithoutborders.org contacted me about helping to create a session focused on Cultural Astronomy. He had just read the latest Communicating Astronomy to the Public Journal Issue which I edited (www.CAPjournal.org). The issue focuses on International Year of Astronomy 2009 activities that included a cultural astronomy component. Mike wanted to build on that idea for the conference panel. Working with Mike and Chris Phillips of the Imiloa Science Center in Hilo, Hawaii, we finally settled on a unifying panel theme for the conference: Indigenous Astronomy and the Public. I have to write the description for our submission. We will have speakers talking about the Indigenous Astronomy of Hawaii, Iran, and South Africa! However, they all haven’t said “Yes”, yet.

I just had a two hour Skype session with the host of Chapter, Verse, & Volume, Heru-Ka Anu. He is doing a review of “African Cultural Astronomy”. The volume came out this week in paperback…but it is the same price as the hardcover! In the interview which he will edit down to one hour, we talked about the text, African American astrophysicists, thinking like a scientist, Benjamin Banneker, and the disenchantment of the night sky in Africa. I’m not sure what will be in the final, but it will air this Sunday at 8 pm EST. www.blogtalkradio.com/herukaanu.

I am writing a short paper on African Cosmology this weekend. Next week Astronaut Hoffman is visiting Pretoria and I am going to be there along with NSBP’s Charles McGruder.