Monday, November 9, 2015

I Am Seeking Your Advice on a New Project

I have been blogging about science for five years without asking for any favours from my readers.  Today, I want your advice on something.

Why you?  The fact that you are here, on this site, means that you are probably science-minded and thoughtful.  Perhaps you also value the communication of science ideas.  Finally, maybe you are the type of person that would like to discuss science and engage in experiments and design in a casual setting with family, friends, and even strangers.

Over the coming year, I would like to develop a new kind of workshop.  At this point, I have a vision for what it might consist of, but the details are a blank canvas.

The workshops that I envision could take place in a library or school, perhaps once a week.  Each workshop could have a theme, and would entail a presentation, discussion, experiment, or design, or a combination of these.  I foresee groups of four to six people interacting in a relaxed setting.

I am looking for your advice for such a project.  Should there be recommended age groups?  Have you already participated in such a thing, and if so, what was good about it and what wasn't?

Why am I doing this?  For a few reasons, but the bottom line is that I don't think there is a place for families and friends to do real science together.  It seems to me to be an underserved market.

If you have any comments, please leave them here, below.  If you are in the Montreal, QC area and would like to be involved in the creation of or attend such a workshop, please feel free to send me a message at stephen.cohen(at)

Thanks.  SC.

Friday, September 11, 2015

This Radiologist Needs to Brush up on her Mechanics

Last week, I injured my shoulder playing soccer; it slammed to the ground after a nasty tackle in my 'friendly' soccer league.  After some nagging from my wife and a few of my students (who got to see what my left hand writes like at the board), I went to get some X-Rays of my right shoulder region taken.

Once in the room with the young radiologist, I was shown where to stand, somewhere between an emitter and receiver of the X-Rays.  She needed to make slight adjustments to my position between exposures.  She would place her hand on my shoulder and/or hip, and push or pull me to the right spot.  And each time it was time to move me, she would state, "Sir, please let me move you."  Eventually, this became, "Sir, please relax and let me move you."  Her frustration seemed to grow as she finally uttered, "Sir, please stop resisting being moved."

I must say, throughout all of this, it took every ounce of my patience to not say: "Enough! I can't take it anymore! Let me explain some basic laws of mechanics to you..."

First off, you cannot push or pull me without being pushed or pulled yourself.  That is Newton's third law, which, if ever violated, would send shock waves through the scientific community.  So, if you expect to push or pull me without getting pushed or pulled back, you must be new at this job.

Second, the extent to which I push back when you push me is related to my inertia or mass.  The amount that you accelerate me from rest with your force has a limit.  It is not a matter of "relaxing my muscles" - the only way you will feel no resistance is if I have no mass.  By saying "Stop resisting being moved," you are essentially telling me to "Stop having mass."  Mass, or inertia, is defined as resistance to linear acceleration.

In the end, I thought it would be smart not to lecture the radiologist about Newton's Laws of Motion.  I held back my urge to scream "Have you never heard of Isaac Newton?"  After all, she was in charge of the amount of high-frequency electromagnetic waves that would be periodically travelling through my body.  She could have responded, "Have you never heard of James Maxwell?"

Wednesday, September 2, 2015

In This House, Mom and Dad Make the Electric Field

In a family with two daughters, aged 3 and 6, the existence of household rules is pretty much a given.  My wife and I are probably lenient compared to many other parents, but maintaining a good environment at home does require some guidelines that the kids come to know.

As I was lecturing about the concept of an electric field yesterday, most of those who were awake were largely unimpressed by the rather abstract concept.  So, here is my attempt to make an analogy so the idea can sink in.

Let us consider my wife and I as "source charges" and our two children as "test charges".  Then, let's label our household rules our "electric field".

The source charges generate the electric field, and the test charges follow them, or go against them, depending on the sign of their charge.  Us parents make the rules, and if one of our daughters is feeling positive, or, agreeable, they follow them.  If she feels confrontational at a given moment, she will surely go against the rules, even if the rule is "eat this chocolate bar" (did I mention I have a 3-year-old?).

Those familiar with the concept of an electric field, realize that in the above analogy, the extent to which a rule is followed or not represents a force.  The relationship between the electrostatic force onto a test charge q in an electric field E is simply: F = qE.  The force onto a test charge within an electric field will either be in the direction of the field or exactly opposite to it.

It is appropriate to equate the electric field to an environment, because that is just what it is.  The rules of the house exist even when a child is not home to obey them or not.  Also, a field has a given direction and magnitude that varies in space.  The rule (direction) in the entrance-way is "take off your shoes when you come in the house," but it is kind of a soft rule that is defied on a daily basis.  "Don't hit your sister!" on the other hand, applies in all spaces and is associated with a large magnitude.  For that reason, when the rule is broken by a negatively charged child, the reaction to it is pretty serious.

A big point of contention in class whenever introducing this concept is "Why don't test charges affect the electric field?"  It is a matter of definition: the source charges establish the electric field - the equivalent to the standard reply "Because we're the parents and we say so."  When the kids grow up, maybe they can become small source charges in the house and have some say on the rules, but not yet.

By definition, an electric field at a given point in space indicates the hypothetical force that would act on a positive charge were it situated there.  Similarly, the rules of the house are made with the presumption that they will be followed by positively charged children.  Right.  My wife and I will need to take a close look at the field we generate, particularly as our little test charges become teenagers.

Monday, August 24, 2015

Locating the Sun Whenever

At around dusk on a recent evening, I came to a logical conclusion while staring up at the half moon in the blue sky.  The Sun was hidden by this time, but I was able to draw a conclusion about its whereabouts.  I just needed to use the Moon as a guide.

First, let vector v1 point from you to the center of the Moon.  Second, let vector v2 point from the center of the Moon to the vertex of the lit up part (as shown below):

Vectors v1 and v2 form a plane.  The center of the Sun lies in that plane.  Think about it.

Thursday, July 9, 2015

Rationing on an Island

I almost never watch television programs other than live sports, and truly never watch 'reality' programs.  However, I made one exception this summer when I tuned in regularly to "The Island".  Over six episodes, the last of which aired this week, a group of men, fourteen initially, were dropped on a hot deserted island with the clothes on their backs, two water canteens, some machetes, and some video camera equipment to record the 28 day experience.  After those 28 days on the island, nine of the men remained, the other five having experienced severe health problems and requiring evacuation.

The first thing that strikes me in a situation like this is just how difficult survival is/was pre-industrialization.  I get that kind of feeling when I go camping, and I 'rough it', you know, with all of my camping equipment and food prepared and packed beforehand.

The enduring thought that stays with me from the show, however, is the idea of limited resources in a group, and the importance of rationing.  The group of men needed to assess their resources and share them fairly amongst them in an amount that would ensure their survival.  Imagine life in a small group on an island where resources are scarce.  If the goal is survival of the group, then rationing water and food is an absolute necessity.

The thing is, mankind as a whole does live on an island - a great big one - the surface of this planet, which trudges along lonely in the solar system.  Our resources are indeed finite, yet we act as though this is not the case.

Thursday, June 4, 2015

The Cohen Condition for Extinction

It is getting harder and harder to make a name for yourself in the science world.  Harder still, if, like me, you would like it to happen without putting forth much effort.

It seems as though it's all been done.  What's left?  The unification of general relativity and quantum mechanics?  That problem, which has stumped all of the greatest minds over the past half century?  I have an engineering background and teach college-level physics - it ain't gonna happen.

But, I had an epiphany recently.  If getting an equation named after you requires something novel, then maybe rather than try to push the boundaries of knowledge, I should think of something that is extremely simple.  There are probably ideas out there so stunningly obvious that academics didn't bother to point them out.

I'm not looking for a unit named after me, nor an element on the periodic table - just something to hang my hat on.  So, without further ado, let me unveil "The Cohen Condition for Extinction"...

Let N = TB - TD,

where TB is the total number of births for a given species throughout all of history

and TD is the total number of deaths for a given species throughout all of history.

If N = 0, the species in question is currently extinct.

If N = 1, the species in question will soon become extinct.

Again, to reiterate, I am not after the Nobel prize.  Ed Witten can keep his Field Medal.  Just having my name in some textbook will satisfy my ego.

Tuesday, March 17, 2015

Magnetism the Most Magical of Forces

Nothing impresses a child more than magnets.  OK, maybe balloons, but magnets are a close second.  Give two magnets to a five year old and that is a solid hour of entertainment right there.  The magnetic force is not like the 'ever-present' gravity in our day-to-day lives.  It seems to be the result of some special, 'magical' force that we observe from time to time.

At the start of my electricity and magnetism course, I usually emphasize that although the electrostatic and magnetic forces are of the same family of forces, they must not be confused as the same thing.  The average person interacts with both of these forces daily and has little understanding of either.  It takes a while to wrap one's head around magnetism, but let's give it a try...

The mere presence of a charge creates an electric field, which can exert an electrostatic force upon another charge.  This is the basis of electrostatics.  In order for a magnetic field to be produced, charge must be in motion.  It then follows that for a charge to experience a magnetic force within a magnetic field, it too must be in motion.  This is the basis of magnetism.  So, whereas all charges produce and respond to electric fields, only those in motion produce and respond to magnetic ones.

The electrostatic force acting on a charged particle in an electric field is quite straight forward:

Here, charge q responds to electric field E.  What makes this force kind of intuitive is that the force points along the same axis or exactly opposite to that of the field (depending on the sign of the charge).  Contrast that with the magnetic force, which acts on a charged particle as follows:

Friday, December 19, 2014

The Physics of "Gravity" and "Interstellar"

Hanukkah is a Jewish holiday celebrating a miracle whereby oil sufficient for just one day burned for eight.  Over this past week, an entirely different miracle took place: I, a father of two young girls watched two movies, none of which contained a single princess.

I really got my nerd on: I rented "Gravity" and then went to the theater to see "Interstellar".  Both films feature a lot of physics, but they could not be more different.  "Gravity" is a ninety minute expedition featuring orbital mechanics, while general relativity weaves its way through the three hours of "Interstellar".

You are probably expecting me to dissect these two films and expose all of their scientific inaccuracies.  In truth, I enjoyed both of them immensely, but would like to address one major problem with each one.

Wednesday, December 10, 2014

Deep Breaths During Exam Time

Over the past weeks and months, I have witnessed some distraught students.  Young adults who walked into the semester cool as a cucumber are hitting the finish line exasperated - not all of them, but many.  A few have asked me for advice, and all I can seem to muster is "Breath".

I thought that I would strive here for something deeper and perhaps more helpful than this.  At the same time, I'll toss in a science metaphor, cause that is sort of my thing.

We are all aware of the need to manage our stress level.  Everyone has their own coping mechanisms for this, so I won't say "Go to the gym" or "Get more sleep" - it's good advice, but I want to focus instead on the bigger picture.

One thing that has been important for me is setting reasonable expectations.  I was not always good at this.

Thursday, November 13, 2014

Rosetta Mission and Noodle Bridges

A couple of unrelated engineering feats occurred yesterday, and I'd like to address them.

First off, the European Space Agency (ESA) succeeded in landing a probe (Philae) on a comet (67P) for the first time in history.  The level of difficulty of accomplishing such a thing is truly off the scale.

A comet is tiny, 'celestially speaking'.  The mass of 67P is about 10^13 kg.  That's a one with 13 zeros attached to it.  But that makes its mass about 100,000,000,000 times lower than that of a typical planet.  Another aspect that makes docking with such a body tricky is its irregular, peanut-like shape.  It is far from a sphere (largest dimension about 5 km, and smallest about 2 km).  Still, regardless of where you land on this comet, the surface gravity is on the order of 0.001 m/s/s (about one ten-thousandth that of the Earth).  So, if you want to dock, you'd better hang on, because escape velocity is only about 1 m/s (jump, and you now orbit the Sun).