My Favorite Web Applications - Part 6

Previous posts:

My favorite web applications - Part 1

My favorite web applications - Part 2

My favorite web applications - Part 3

My favorite web applications - Part 4

My favorite web applications - Part 5

Continuing on with my pet project here, this next web application is actually another one of those that closely mimics an actual experiment. This time, it is on specific heat, and the goal here is to measure the specific heat of an unknown liquid. You do this by measuring the mass and temperature of the unknown liquid, and then mixing it with hot water of known mass and temperate. By finding the final equilibrium temperature, you then calculate the specific heat of the unknown liquid.

Like I said, this web experiment is done step by step just like a real experiment. In fact, you could use this as the lab instruction and get the students to follow each step of the experiment. But what I like the most is that each student will be given a different set of numbers to work with. The masses will be different, and so will the starting temperatures of the liquid, resulting in different final temperature as well. I don't remember if the specific heat of the unknown liquid is also different for different students. Please let me know if you've used this app or if you discover this later on.

I used this as one of my virtual labs when we went remote. But I continue to use this after we gone back to face-to-face classes as part of my in-class problem solving exercises. I've also given this as a take-home homework problem, and they have to show the final acknowledgement page that they got this correct if they want to receive credit for it. If the students have done the actual experiment itself, this web application will be quite familiar and they should have a good clue on how to correctly find the unknown specific heat.

Zz.

My Favorite Web Applications - Part 3

Previous posts:

My favorite web applications - Part 1

My favorite web applications - Part 2

Continuing with this series, here is my next favorite web application. This is a virtual experiment on measuring the specific heat of an object. The fun thing about this particular application is that (i) it is very similar to what we normally do in a real experiment and (ii) one can also use the step-by-step instruction as part of the experimental procedure, thus the name "Guided Specific Heat.... ".

Similar to the force table experiment that I cited in Part 2, this one also has randomized values for each person going through it. It randomizes the mass of the cold water, the mass of the object, and uses different specific heats. Each student doing this online will have a different answer.

When I assigned this to the students during our remote sessions, the students had to fill in all the information obtained during each step, i.e. measurement of the mass, etc. Then, during the actual measurement, once it stopped, the students had to do a screen capture of the graph of Temp. vs. time to paste in their report. They then had to show their work on how they arrived at the specific heat value of the object. If they entered the correct answer, the application acknowledges that and they should also do a screen capture of that to paste in the report. If they got it wrong, then they had the option of either submitting what they had and take the deduction for the wrong work and answer, or redo the experiment from the very beginning. They get to do this as many times as they wish until they get it right.

I also added an extra part where I asked them to think of the kind of errors and uncertainty in the experiment, especially if this were done in real life.

To double-check the students' answers, I created a spreadsheet where all I needed to do was to enter the mass of the object, mass of the cold water, and the final temperature. 

I like that each student will have a different answer. It added an extra layer where they could not just copy off each other's work directly. The experimental procedure is also almost identical to one of our experiments on specific heats anyway, so I didn't have to make huge modification to the instruction.

Now that we have gone back to f2f classes, I'm using this exercise as part of a homework assignment.

Zz.

The Physics Of Baking Pizza

For those who are purist and prefer the thin-crust, Neopolitano-style pizza, this one might be right up your alley.

This preprint on ArXiv tackles the question on whether baking such pizza is better done in a stone over rather than the standard metal ovens. Which one do you think will win?

Stone ovens heat up to very high temperatures, higher than typical home ovens. But ceramic or stone surface also has low thermal conductivity while having a high specific heat. It means that it retains heat longer and does not cause the dough to burn. It is why this is also the preferred way to bake rustic, crusty bread.

I guess we all just have to build a brick pizza oven in our backyards! :)

Zz.

Mpemba Effect Is Still Hot After All These Years

OK, maybe not hot, but it is certainly at least lukewarm.

If you don't know anything about this, I've made several posts on the Mpemba effect before (read here, here, here, and here). Briefly, this is the effect where hot water is seen to freeze faster than cold water. Even after its purported discovery many years ago, the validity of this effect, and the possible explanation for it are still being debated.

Add this report to the body of discussion. It seems that there are new papers that are using molecular bonds in water as the possible explanation for this effect.

Now researchers from the Southern Methodist University in Dallas and Nanjing University in China think they might have a solution - strange properties of bonds formed between hydrogen and oxygen atoms in water molecules could be the key to explaining the elusive Mpemba effect.

Simulations of water molecule clusters revealed that the strength of hydrogen bonds (H-bonds) in a given water molecule depends on the arrangements of neighbouring water molecules.

"As water is heated, weaker bonds break, and groups of molecules form into fragments that can realign to form the crystalline structure of ice, serving as a starting point for the freezing process," Emily Conover reports for Science News.

"For cold water to rearrange in this way, weak hydrogen bonds first have to be broken."

I'm sure this will not be the last time we hear about this.

Zz.

Football Physics and Deflategate

This issue doesn't seem to want to go away.

Still, anyone who has been following this (at least here in the US) have heard of the "Deflategate" controversy from last year's NFL Football playoffs.

Chad Orzel has another look at this based on a recent paper out of The Physics Teacher, this time, from the physics involved with the football receivers.

Most of the coverage of “Deflategate” has focused on Patriots quarterback Tom Brady, and speculation that he arranged for the balls to be deflated so as to provide a better grip. The authors of the Physics Teacher paper, Gregory DiLisi and Richard Rarick look at the other end of the problem, where the ball is caught by the receiver, thinking about it in terms of energy, an issue with major implications for the existence of atomic matter.

It certainly is another angle to the issue. I hope to get a copy of the paper soon and see what it says.

Zz.

The Physics Of Air Conditioners

Ah, the convenience of having air conditioning. How many of us have thanked the technology that gave so much comfort during the hot, muggy day.

This CNET article covers the basic physics of air conditioners. Any undergraduate student who had taken intro Physics course should know the basic physics of this device when studying thermodynamics and the Carnot cycle. This is essentially a heat pump, where heat is transferred from a cooler reservoir to a warmer reservoir.

But, if you have forgotten about this, or if you are not aware of the physics behind that thing that gives you such comfort, then you might want to read it.

Zz.

Arrow Of Time Due To Gravity?

I just got back from vacation and an unexpected trip out of the country, so I'm still catching up. But when I came across a news article on physics in Business Insider, I had to read it, and you should to. It is on another model to explain the nature of the arrow of time in our universe.

Tentative new work from Julian Barbour of the University of Oxford, Tim Koslowski of the University of New Brunswick and Flavio Mercati of the Perimeter Institute for Theoretical Physics suggests that perhaps the arrow of time doesn’t really require a fine-tuned, low-entropy initial state at all but is instead the inevitable product of the fundamental laws of physics. Barbour and his colleagues argue that it is gravity, rather than thermodynamics, that draws the bowstring to let time’s arrow fly. Their findings were published in October in Physical Review Letters.

The team’s conclusions come from studying an exceedingly simple proxy for our universe, a computer simulation of 1,000 pointlike particles interacting under the influence of Newtonian gravity. They investigated the dynamic behavior of the system using a measure of its "complexity," which corresponds to the ratio of the distance between the system’s closest pair of particles and the distance between the most widely separated particle pair. The system’s complexity is at its lowest when all the particles come together in a densely packed cloud, a state of minimum size and maximum uniformity roughly analogous to the big bang. The team’s analysis showed that essentially every configuration of particles, regardless of their number and scale, would evolve into this low-complexity state. Thus, the sheer force of gravity sets the stage for the system’s expansion and the origin of time’s arrow, all without any delicate fine-tuning to first establish a low-entropy initial condition.

Zz.

Lights On Pipes - Which One Heats The Most?

We also deal with elementary stuff here.

The people at the Frostbite Theater at JLab has another video out. This time, they show an experiment on which pipes heats the most when shined with light.



The results is not surprising. But what is surprising is why the white pipe heats up faster initially. So, anyone wants to enter a Science Fair to study why this is so, especially when Steve is way too old to enter?

Zz.

Making Better Fog With Dry Ice

In case you are ever in a school play that requires a lot of fog.....



Zz.

Is There A Link Between Intelligence And Entropy?

It's an interesting question, and there are certainly models that point to such a link. The latest one is a very clear example the strong possibility that intelligence can be linked to entropy.

Entropy measures the number of internal arrangements of a system that result in the same outward appearance. Entropy rises because, for statistical reasons, a system evolves toward states that have many internal arrangements. A variety of previous research has provided “lots of hints that there’s some sort of association between intelligence and entropy maximization,” says Alex Wissner-Gross of Harvard University and the Massachusetts Institute of Technology (MIT). On the grandest scale, for example, theorists have argued that choosing possible universes that create the most entropy favors cosmological models that allow the emergence of intelligent observers.

This, I think, would give some degree of a quantitative description of intelligence, a characteristics that so far defy such a clear description. And yes, I'm discounting the silly IQ test as a measure of intelligence. Linking it to a concept in physics allows for a more definite foundation to define and measure intelligence.

Will be fascinating to see how far this will lead.

Zz.

The Physics Of Toasty Buns

It's summer (at least, here in the northern hemisphere), and lots of outdoor grilling goes on. So what a timely article on the secret to getting proper grilling of food.

At high temperatures -- about 400 degrees and up -- a substantial part of the heat that reaches the food arrives in the form of infrared light waves rather than via hot air or steam.

The higher the temperature, the bigger the part that radiant heat plays in cooking. But this form of heat interacts with color in a profound way.
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A silvery, mirror-like fish skin is even more reflective than a white car. About 90 percent of the radiant heat striking it simply bounces away. Because only around 10 percent of the energy sinks in and warms the fish, cooking initially creeps along slowly but steadily.

That changes rapidly, however, as soon as the food gets hot enough to brown. It's like changing from a white shirt to a black shirt on a sunny summer day.

As the food darkens, that 10 percent of energy absorbed rises by leaps and bounds, and the temperature at the surface of the food soars.

So learn your physics to understand how to be good in grilling! :)

Zz.

Can You "Feel" Temperature?

Another fine video, and might answer the question (if you have it) on why a metal feels colder than a book, even when both are at the same temperature.



Zz.

Lifting Lemon

This is a simple experiment, and variations of this have been done in many classroom demonstrations, I'm sure. But it still becomes a topic of discussion as to why it happens, as demonstrated by the discussion on this video's YouTube page.



This link provides an explanation for this effect.

Zz.

Breaking Time-Reversal Symmetry Reduces Thermodynamic Efficiency

This was reported a few days ago, but I've only had a chance to read it recently. It is an interesting calculation for the thermodynamic efficiency of a thermoelectric engine in the presence of an external magnetic field, thereby breaking the time-reversal symmetry.

In this spirit, Kay Brandner at the University of Stuttgart, Germany, and colleagues report in Physical Review Letters their calculated efficiency of a simple thermoelectric device that converts heat to electrical current (Fig. 1). They show that when the device operates in an external magnetic field—a condition that breaks time-reversal symmetry for the motion of electrons—the efficiency is significantly lower than previous studies predicted. The lower bound on efficiency occurs, they argue, because in addition to the requirement that entropy be greater than or equal to zero, charge must be conserved—a point that was missed in earlier work. Their findings improve our understanding of thermoelectric efficiency and may one day influence the design of thermoelectric devices for real-world applications.

The rest of the article has a very good detail on why this is such an important study. You also get a free copy of the paper in the link.

Zz.

The Physics of Firewalking

You get a rather good article on the physics of firewalking, and you don't even have to pay $2000 for it. You get it for FREE! Such a deal!

Last Thursday, close to two dozen participants at a motivational seminar hosted by Tony Robbins suffered burns on their feet, while attempting to tromp across lanes of red-hot coals. So what did these burn victims do wrong?
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A layer of ash atop the coals serves as an additional protective barrier. Like the coals beneath it, ash is a poor conductor of thermal energy (so poor, in fact, that it has a history of use as insulation material in ice boxes). Add to this the fact that the ash is no longer producing any heat itself, and one can begin to appreciate how walking over a bed of 2000-degree coals might be possible.
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If I had to guess what happened with the people who suffered burns Thursday night, I'd say that they spent too much time looking into "the power within themselves" and "focusing on walking on the fire," and not enough time focusing on actually getting themselves off the coals.

Some time, some people shouldn't be saved from themselves.

Zz.

£1000 Reward For The Best Explanation Of The Mpemba Effect

This thing will just not go away! :)

The UK Royal Society of Chemistry is offering a £1000 cash prize for the best explanation for the Mpemba effect. This is where hot water appears to freeze faster than cold water.

It's a question that has perplexed scientists for centuries and now the Royal Society of Chemistry is offering £1000 to whoever can come up with the best explanation for what is referred to as the The Mpemba Effect.

Judges will be looking for an outside-the-box submission that is creative and eye-catching.

The deadline for submissions is July 30.

Creative and "eye-catching"? What about being CORRECT and verified?

Hum.. oh well. The link to the contest is here where it is described in a bit more detail:

Submissions can be based on, and reference, existing research. The winning submission will be scientifically sound, and arresting in presentation and delivery. The judges' decision will be final.

We shall see! If you want to catch up on all the stuff I had linked to on this effect, click here, here, and here.

Zz.

Maxwell's Demon Exorcised?

Heh, sorry. Couldn't help with the pun.

It appears that there's now experimental evidence that erasing information requires the expenditure of energy. Consequently, this energy defeats the scenario presented in the Maxwell's Demon.

The results safeguard one of the most cherished principles of physical science: the second law of thermodynamics. This law states that heat will always move from hot to cold, or equivalently, that entropy — the amount of disorder in the Universe — always increases.

In the nineteenth century, the Scottish scientist James Clerk Maxwell proposed a scenario that seemed to violate this law. In a gas, hot molecules move faster than cold ones. Maxwell imagined a microscopic intelligent being, later dubbed a 'demon', that would open and shut a trapdoor between two compartments to selectively trap hot molecules in one of them and cool ones in the other, defying the tendency for heat to spread out and entropy to increase.

Landauer’s theory offered the first compelling reason why Maxwell’s demon couldn’t do its job. The demon would need to erase (‘forget’) the information it used to select the molecules after each operation, and this would release heat and increase entropy, more than counterbalancing the entropy lost by the demon.

It is very difficult to go against the 3rd Law, I tell ya!

Zz.

Freezing Egg In Liquid Nitrogen

More fun video from those folks at Jlab! This time, based on someone's suggestion, they froze an egg.




Unfortunately, there aren't a lot of physics discussion in the video itself. If you go to the YouTube site for this video, you get a bit more of some of the physics surrounding this demonstration in the discussion and comments. The one thing they asked was why it took 8 minutes to freeze the egg, but it took 2 hours to thaw it, even when the temperature change is the same. This is a good question to ask the kids! :)

Zz.

Freezing Liquid Nitrogen

Those fun people at JLab are at it again. This time, they freeze liquid nitrogen using evaporative cooling.



Zz.

More on the Mpemba Effect

This effect seems to have a life of its own, and certainly generating a lot of interesting discussion and experiments. I've mentioned previously on such studies that studied this effect more closely. Well now comes another one, and this one has a slight twist to it[1].

Abstract: Unlike most of the research on the Mpemba effect which has focused on verifying the observation that warm water freezes faster than cold water, our work quantitatively investigates the rates at which hot and cold water cool and the point at which hot water reaches a lower temperature than cold water under a set of external conditions. Using a vacuum pump to cool samples of water initially at different temperatures, we measured reproducible temperature values at which hot and cold water equilibrate. We have confirmed that warmer water indeed cools at a faster rate than colder water and that, surprisingly, this trend continues past the point where the temperatures of the two samples are the same. Our results show that when using optimal initial temperature conditions, the crossover temperature is found to be 2.7 oC whereas our other set of initial conditions gave a crossover temperature of -0.07 oC. These data taken together provide a definite quantitative evidence of the Mpemba effect.

There you have it. We just have to wait and see if this gets published.

Zz.

[1] http://arxiv.org/abs/1101.2684