Which Comes First, Energy Or Momentum?

First of all, Happy New Year! It's my first post of 2023. I'm crossing my fingers that I won't be as stressed out as I was toward the end of 2022.

As I prepare for another semester of teaching General Physics, I'm struck at trying to understand the logic in the sequence of the introduction of the topics on energy and momentum. I know that as instructors, we have the freedom to arrange the sequence that we introduce the topics that we teach, so this is not a criticism. Rather, it is just trying to understand if there is a rational reason for introducing one ahead of the other.

I'm talking in particular about the topics of momentum and energy. This is because different textbooks introduce them in different order. I'll list a few examples.

• Serway-Jewett: "Physics for Scientists and Engineers" 10th ed. - Energy Chap. 7&8; Momentum Chap. 9.
• Knight: "Physics for Scientists and Engineers" 4/e - Energy Chap 9&10; Momentum Chap. 11.
• Knight-Jones-Field: "College Physics" 4e - Momentum Chap. 9; Energy Chap. 10.
• Giancoli: "Physics - Principles with Applications" 7th ed - Energy Chap. 6; Momentum Chap. 7.
• Hewitt: "Conceptual Physics" 13th ed - Momentum Chap. 6; Energy Chap. 7.

As you can see, different authors/textbooks introduce momentum and energy in different order. My question is, WHY?

From my view, it is more logical to introduce the concept of energy FIRST, and then introduce momentum. This is because a large part of momentum, and real-world cases of collisions, involves inelastic events in which kinetic energy is not conserved. So how does one ignore inelastic collisions when dealing with conservation of momentum? Or, if one does include inelastic collisions, how does one tip-toe around it when the concept of energy (kinetic energy) has not been introduced yet? 

Has anyone done this using the sequence of momentum first and then energy? How did you go about doing it? Is there a rational reason for introducing the topic this way?

Zz.

We Have Ignition!

So the big news of the week, which was preceded by the rumors a few days before the official announcement, is the breakeven achievement in a fusion process at Lawrence Livermore's National Ignition Facility (NIF).

This is certainly a major breakthrough, and it is something that has achieved for the very first time ever in a controlled experiment (it happens all the time in our Sun and other stars). However, to me, this is more of a proof-of-principle experiment, meaning that it is a demonstration that it is possible, rather than to show that it is viable. It is certainly very, VERY far away from producing anything useful because harnessing this energy is an entirely different matter.

While you can read many sites reporting this, I kinda like the one that I read on CNET because there's a certainly level of sensibility aimed towards the general public. In particular, there is this definition of what is meant by "breakeven":

More specifically, scientists at NIF kickstarted a fusion reaction using about 2 megajoules of energy to power the lasers and were able to get about 3 megajoules out. Based on the definition of ignition used by NIF, the benchmark has been passed during this one short pulse. 

But that doesn't convey the whole thing, because this is what should also be mentioned:

"The calculation of energy gain only considers the energy that hit the target, and not the [very large] energy consumption that goes into supporting the infrastructure," said Patrick Burr, a nuclear engineer at the University of New South Wales.

What it means is that they only considered the energy of the laser hitting the target, and then finding the energy output from the ignition that subsequently resulted in fusion. Sure, that energy output is greater than the input energy of the laser, but this is not the total energy of the entire facility that created the laser. That facility would still not be self-sufficient to run just by using the output energy of the fusion it created, even assuming 100% efficiency.

This does not diminish the amazing achievement, considering that other facilities and techniques have not even reach this level. It is just that it needs to be tampered with a bit more realistic expectations so that we don't oversell ourselves to the public.

Zz.

How Classical Kinetic Energy Is Actually A Subset Of Relativistic Kinetic Energy

Many people think that Classical Physics and Relativistic Physics are two different things. Of course, anyone who has studied both can tell you that one can derive many of the classical physics equations from relativistic equations, proving that classical equations are actually special cases of the more general relativistic equations.

In this Don Lincoln's video, he shows how classical kinetic energy that many students learn in General Physics courses can actually be derived from the more general relativistic energy equation, and why we still use the classical physics equation in most cases.

Z.

The Physics Of Your Vehicle Gas Mileage

While fuel prices are not as high as they were a few years ago, gas/petroleum cost is always a factor in our lives if we drive often.

This article reveals the physics of your vehicle gas mileage, and what may cause it to be better or worse than others. We can add this to another entry on this similar topic that I posted earlier.

Zz.

NIF Achieves Milestone

Finally, some good news out of the National Ignition Facility.

In a paper published in Nature, Hurricane and colleagues report results from experiments carried out last September and November – the former producing 14 kJ of fusion energy from a single laser shot and the latter 17 kJ. The researchers point out that since the energy delivered to the fuel is about 10 kJ, both shots generated a fuel gain. They also calculated that as much as half of the energy output from these shots originated in alpha-particle heating. This is significant because such heating is a prerequisite for ignition.

They haven't achieve ignition yet, but this is certainly a necessary step towards understanding this whole process. Now, they have the difficult and unenviable task of delivering on the promise.

Zz.

Energy Theater?

I've read the "press release" of this work, but only had a quick glance at the paper. But that should not stop you from having a look at it.

This activity for elementary/primary level education is meant to give a rather visual representation of the concept of energy, the ability of energy to transform from one form into another, and the conservation of energy principle.

In the current study, the researchers report their ongoing examination of an activity that they have created, called "Energy Theater." Energy Theater is specifically designed to help learners visualize energy and how it dynamically changes form and location. In Energy Theater, learners (K-12 science teachers in this study) each play the role of one "chunk" of energy, and indicate with hand gestures what form that energy has (e.g., chemical, motion, gravitational, thermal). Different objects are represented by loops of rope on the ground, and learners can move from object to object, demonstrating energy moving between those objects. While energy is not actually a material substance, this metaphor can help learners think about how a fixed amount of energy can flow between different objects.

For example, the group may be given the problem of, "Show what happens when a hand pushes a box across a table." Participants would first stand in the area representing the hand, making the gesture for "chemical energy." One by one, they would move to the area representing the box, changing their gesture to "energy of motion." Other scenarios might include how energy flows when an incandescent light bulb is turned on. The group must work together to decide how the "theater" will play out for a particular situation, making complicated decisions about just where and when the energy will flow and take different forms. 

It sounds rather convoluted to me, but that is probably because I haven't had the chance to actually see it. Maybe something like this can sink in easier with students at that age and level.

In any case, you should be able to read the actual publication that appeared in PRST-PER that gives free access.

Zz.

More On Driving And Saving Fuel

So I was driving along the US Interstate over the weekend, and stopped at a rest area on an Illinois interstate (we call them Oasis over here) highway. In the washroom, they have these posters placed in several places, and one of the posters has these things that tells you some "green" driving tips. One of the tips given was something that I had brought up quite a while back. It is on driving with your windows down.

The poster here said this:

Try using vents and opening windows to cool off before you turn on the air conditioner. Air conditioning increases fuel consumption.

Now, if you've read my earlier post when I asked about this, you will also have read the two comments left behind, including one on an investigation done by the Mythbusters folks. Here, it turns out that if one is driving faster than 50 mph, then rolling up the windows and turning on the air-conditioning uses LESS fuel than driving with the windows down and no air-conditioning. The drag forces above that speed causes more use of energy than the air-conditioning unit.

So this poster is not quite up-to-date on "green driving".

Zz.

Sustainable Energy: Fact or Fiction

Hey, if you are in the Chicagoland area, this might be something you want to attend, considering that this is certainly an important and relevant topic nowadays. It is a talk on sustainable energy by Argonne's George Crabtree.

Tuesday, January 31, 2012
Illinois Institute of Technology (IIT)
McCormick Tribune Campus Center
McCloska Auditorium
3201 South State Street

Let me know if you are attending it. I'd appreciate a report.


Zz.

Fusion Power

This is an Op-Ed in the NY Times by Stewart C. Prager, director of the Princeton Plasma Physics Laboratory, on why investment in fusion power research is critical.

But an abundant, safe and clean energy source once thought to be the stuff of science fiction is closer than many realize: nuclear fusion. Making it a reality, however, will take significant investment from the government at a time when spending on scientific research is under threat.

Harnessing nuclear fusion, the energy that powers the sun and the stars, has been a goal of physicists worldwide since the 1950s. It is essentially inexhaustible and it can be created using hydrogen isotopes — chemical cousins of hydrogen, like deuterium — that can readily be extracted from seawater.

 Of course, in the current political climate in the US, funding and commitment to fusion technology in the US is lagging behind several nations.

However, even though the United States is a contributor to this experiment, known as ITER, it has yet to commit to the full program needed to develop a domestic fusion reactor to produce electricity for the American power grid. Meanwhile other nations are moving forward to implement fusion as a key ingredient of their energy security.

Indeed, fusion research facilities more modern than anything in the United States are either under construction or operating in China, Germany, Japan and South Korea. The will and enthusiasm of governments in Asia to fill their energy needs with fusion, as soon as possible, is nearly palpable.

Again, not surprising, and it's the same old story. The US is slowly but surely falling behind in an increasing number of scientific areas. I wouldn't be surprised at all that, 50 to 100 years from now, this period for the last 10-20 years will mark the beginning of the decline of the American civilization, just like the decline of other great civilizations of the past.

Zz.

Japan's Nuclear Crisis - Steven Chu Interview

Newsweek interviewed US Dept. of Energy Secretary, Steven Chu, on the aftermath of Japan's nuclear crisis. It didn't just cover his job, but also him being a physicist and still producing his own research work.

Last summer you wrote a paper called “Subnanometre Single-Molecule Localization Registration and Distance Measurements.” When asked about it, you said, “I consider it my equivalent of vegging out in front of the TV.”

The first 80 hours a week of my time go to my full-time job at the Department of Energy. But in the wee hours of the morning, on airplane trips, I can go back and forth. It doesn’t take much time, and it’s a good release.

Zz.

Rush Holt On Japan's Nuclear Crisis

His win over Watson made him a household name among the public. So hopefully, the voting public in the US knows enough about him (and the fact that he is a physicist) to at least pay attention to what he has to say.

And being a nuclear physicist and someone who knows about nuclear reactions intimately (certainly more than the talking head Michio Kaku on TV), he has an expert and unique perspective on the nuclear crisis going on in Japan, and the whole idea of energy source and consumption. This is what we get in this news article. So read it while you have a chance.

Zz.

A Zombie Steven Chu

Our US Energy Secretary commented on his Facebook page on how cool he looks as a zombie. He doesn't think there's evidence that zombies exist (neither do I), but then he talks about vampire appliances.

To date, there is no scientific evidence about the existence of Zombies, but what about vampires? Actually, when it comes to energy, they are all too real. “Vampire appliances” – from DVD players to stereos to desktop computers -- suck up energy even when they are turned off. In fact, these vampires are responsible for adding 10 percent or more to your monthly electricity bill.

That's scary. So Happy Halloween, everyone!

Zz.

Steven Chu's OpEd in The Times

US Energy Secretary Steven Chu wrote an Opinion piece in The Times. The essay concentrates mainly on energy consumption and the environment. The Times' synopsis on Steven Chu says it all:

MEET OBAMA’S NEW GREEN MAN On December 15, 2008 President Obama announced the appointment of Steven Chu as US Energy Secretary, a move that heralded a new era in the White House. Dr Chu is a pioneering Nobel prize-winning scientist devoted to the issue of climate change. The contrast with the Bush years could hardly have been greater.

Zz.

Let's Get Real About Energy

This is a rather good and eye-opening article. It gives, in very simple terms, the level of energy consumption using comparison that many people can understand.

Let's express energy consumption and energy production using simple personal units, namely kilowatt-hours. One kilowatt-hour (kWh) is the energy used by leaving a 40-watt bulb on for 24 hours. The chemical energy in the food we eat to stay alive amounts to about 3 kWh per day. Taking one hot bath uses about 5 kWh of heat. Driving an average European car 100 kilometers (roughly 62 miles) uses 80 kWh of fuel. With a few of these numbers in mind, we can start to evaluate some of the recommendations that people make about energy.

These are numbers that many people can understand. But what is also interesting is the comparison of various possible alternatives energy sources.

As a thought-experiment, let's imagine that technology switches and lifestyle changes manage to halve American energy consumption to 125 kWh per day per person. How big would the solar, wind and nuclear facilities need to be to supply this halved consumption? For simplicity, let's imagine getting one-third of the energy supply from each.

To supply 42 kWh per day per person from solar power requires roughly 80 square meters per person of solar panels.

To deliver 42 kWh per day per person from wind for everyone in the United States would require wind farms with a total area roughly equal to the area of California, a 200-fold increase in United States wind power.

To get 42 kWh per day per person from nuclear power would require 525 one-gigawatt nuclear power stations, a roughly five-fold increase over today's levels.

A very good article.

Zz.

"Green" Energy Initiative Needs A Big Leap

A very good article that discussed the issues surrounding energy efficiency and renewable energy research in the US. It has as much to do with the organizational problems of coordinating and directing such research efforts as it is with the science involved.

There are also roadblocks within the federal government, the Energy Department report and two other new studies suggest. Experts from the Brookings Institution said this month that the way federal energy research was being managed was "holding back innovation and rapid deployment of clean energy technology."

And Harvard researchers said the government had "fallen short in what it can do to promote the development and deployment of advanced energy technology."

All three reports call for more research funding, and they suggest institutional changes to spend research dollars smarter.

Especially when there's a lot of money to be spent after the stimulus package has been passed, it is imperative that some coordinated effort is in place to figure out where the money should go to.

Zz.

Rush Holt on Energy Policy, Barack Obama and John Holdren

I seem to be highlighting a lot of stuff from the NY Times lately, but it's not on purpose. They seem to be putting out a lot of relevant articles that I think deserves to be read, not because we have to agree with it, but because these are important issues and ideas that need to be heard and think about.

This time, they have a brief interview with Rush Holt, one of the 4 (?) physicists serving in the US Congress (I'm using NY Times numbers here, but I thought there were only 3 - Rush Holt, Vernon Ehlers, and Bill Foster. Who am I missing?). In the interview, he gave his opinion on several issues that are at the forefront of politics and science nowadays - Energy policy, President-Elect Barak Obama, and the incoming Presidential Science Advisor nominee John Holdren.

As far as the policy outlined by Barak Obama, he has this to say:

Question
What’s your take on the energy portion of Mr. Obama’s proposed economic stimulus plan? Is there enough in it?

Answer
No, not enough. I think president-elect Obama has the vision. But the economists around him, and the people who are actually putting the economic recovery package together, despite good words, don’t have a deep appreciation of the role of research and development as a short-term, mid-term, and long-term economic engine.

I don’t think that they have an appreciation of the enormity of the response that is needed to address the energy and environmental problems we face.

I think the president-elect gets it, but the people who are putting together the package, although it has many billions of dollars for energy research, for energy conservation, and other things, it doesn’t have enough. I think they are lowballing what we should be putting into research, and what we should be putting into rolling out energy technologies.

Let's see who Obama listens to the most once everyone is in place.

Zz.

APS To Sit Down With Obama's Transition Team This Friday

The American Physical Society (APS) will be meeting with members of Barak Obama's transition team this Friday to discuss ways to improve the energy efficiency. I'm sure they will base their recommendation on the recently released report from the APS on energy conservation and efficiency.

Not a bad start if this can have a meaningful outcome. It is certainly more than what George Bush did when he took office.

Zz.

Energy Future = Think Efficiency

I'm very happy that the APS has launched a report to tackle the US energy issue. We have gotten so many of these things already, but not from the point of view of the science/technology. The APS's webpage claim that this is a different type of energy report.

Energy Future: Think Efficiency differs from other energy efficiency reports in its emphasis on scientific and technological options and analysis. Based on emerging technologies, this report targets which research and development gives America the best return for its dollars.

Want to know what works now, what can work soon, and what is feasible for the future? The Energy Future: Think Efficiency study panel of leading experts in energy policy with backgrounds in physics, engineering, economics, and policy, examines and answers these very questions.

Certainly very timely, and worth paying attention to. I mean, if those global warming opponents got so excited that an article in an APS Division actually presented an anti-global warming argument, then they also can't ignore when the APS itself produces and endorses something like this.

Edit: here's a news article on this APS report.

Zz.

Cow Power Could Generate electricity for Millions, Study Shows

Before you proclaim that this report stinks, you should read it carefully. :)

Scientists at the University of Texas (of course) has published a report that claim that by burning the manure from cows and other livestock, the US could get could get as much as 3% of electricity demand.

Broken down and then burnt, the scientists estimate that the manure from hundreds of millions of livestock in America could produce approximately 100 billion kilowatt hours of electricity a year.

If left to decompose naturally manure releases noxious gases into the environment, some of which warm the atmosphere at a higher rate than carbon dioxide.

Converting it to power could reduce those emissions by 99 million metric tonnes, the equivalent of approximately four per cent of America's emissions from electricity production.

Although the process would emit some carbon dioxide into the atmosphere, it would do so at a lower rate than if coal was used.

While such a claim isn't new, the numbers being presented here is unHERD of previously. I certainly don't think this is UDDER nonsense, but it might be worth looking into.

Moo!

Edit: Here is the exact reference to this work:

Amanda D Cuéllar and Michael E Webber, Environ. Res. Lett. v.3 p.034002 (2008)

Abstract: This report consists of a top-level aggregate analysis of the total potential for converting livestock manure into a domestic renewable fuel source (biogas) that could be used to help states meet renewable portfolio standard requirements and reduce greenhouse gas (GHG) emissions. In the US, livestock agriculture produces over one billion tons of manure annually on a renewable basis. Most of this manure is disposed of in lagoons or stored outdoors to decompose. Such disposal methods emit methane and nitrous oxide, two important GHGs with 21 and 310 times the global warming potential of carbon dioxide, respectively. In total, GHG emissions from the agricultural sector in the US amounted to 536 million metric tons (MMT) of carbon dioxide equivalent, or 7% of the total US emissions in 2005. Of this agricultural contribution, 51 to 118 MMT of carbon dioxide equivalent resulted from livestock manure emissions alone, with trends showing this contribution increasing from 1990 to 2005. Thus, limiting GHG emissions from manure represents a valuable starting point for mitigating agricultural contributions to global climate change.

Anaerobic digestion, a process that converts manure to methane-rich biogas, can lower GHG emissions from manure significantly. Using biogas as a substitute for other fossil fuels, such as coal for electricity generation, replaces two GHG sources—manure and coal combustion—with a less carbon-intensive source, namely biogas combustion.

The biogas energy potential was calculated using values for the amount of biogas energy that can be produced per animal unit (defined as 1000 pounds of animal) per day and the number of animal units in the US. The 95 million animal units in the country could produce nearly 1 quad of renewable energy per year, amounting to approximately 1% of the US total energy consumption. Converting the biogas into electricity using standard microturbines could produce 88 ± 20 billion kWh, or 2.4 ± 0.6% of annual electricity consumption in the US. Replacing coal and manure GHG emissions with the emissions from biogas would produce a net potential GHG emissions reduction of 99 ± 59 million metric tons or 3.9 ± 2.3% of the annual GHG emissions from electricity generation in the US.

Zz.

Home Photovoltaic Systems for Physicists

Just in time for $150 per barrel oil, this is a fun and timely article by Tom Murphy in this month's issue of Physics Today. It deals with the setting up of a modest photovoltaic system to run a suite of appliances. But what is interesting is that it deals with it from the background of what a physicist know. We are not electrical engineers, and while we do know the physics of semiconductor, the practical aspect of setting up something that needs to work at this level isn't trivial.

It was with those concerns in mind that I decided to explore the practical side of photovoltaic energy: In 2007 I built a PV system to power my living room. Though reasonably well informed on the semiconductor physics of PV junctions, I felt unsuitably prepared to evaluate the practical realities of owning and operating a personal solar PV system. Because I believe physicists can play a role in our energy future that extends beyond the confines of advanced research, I want to share my experiences in the hope that others might develop home PV projects. What better way to motivate innovation in the alternative-energy sector than to get a talented pool of physicists engaged on a personal level?

A recommended reading if you don't get a subscription to Physics Today.

Zz.