My Favorite Web Application - Part 8

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

My favorite web application - Part 6

My favorite web application - Part 7

This is another one of my favorite web application because it has a ability to assign random values to various parameters in the problem.

This is a simulation of a motional emf in the form of a rail gun. It actually is a straight-forward application of magnetic force acting on a straight current. One may also solve this using Faraday's law, but it is not as straight-forward to solve because the magnetic flux (or rather, the area) does not change uniformly since the rod is accelerating.

What I also like about this simulation is that one can also tie in with what the students learned in Physics 1, i.e. they may verify their answer using kinematics, since we know the rod's mass, and it starts moving from rest. Knowing how far it travels and a good estimate of the time of travel gives us the value of the acceleration, and thus, the force acting on the rod. This should match with the magnetic force.

Zz.

ChatGPT and Projectile Motion, Part 2

If you missed my previous physics questions to ChatGPT, check them out here and here. 

In this particular case, I asked ChatGPT a rather common question, and ended up having an argument with it. My questions are in red while ChatGPT's responses are in blue.

Three projectiles of the same mass are launched from the top of a cliff with the same initial speed. The first projectile is launched at an angle of 20 degrees above the horizontal. The second is launched horizontally. The third is launched at an angle 20 degrees below the horizontal. Which projectile hit the ground with the largest speed?

All three projectiles are launched with the same initial speed, which means they all have the same initial kinetic energy. The only difference is the angle at which they are launched.

The maximum range of a projectile launched at a given speed is achieved when it is launched at an angle of 45 degrees above the horizontal. This means that the first and third projectiles will have the same range, but the second projectile, launched horizontally, will have a shorter range.
However, the question asks which projectile hits the ground with the largest speed, not which has the greatest range. To answer this question, we need to consider the vertical component of each projectile's velocity at impact.

The first projectile is launched at an angle of 20 degrees above the horizontal, so it will have a significant vertical component of velocity at impact, causing it to hit the ground with a larger speed than the third projectile, which is launched at an angle of 20 degrees below the horizontal and will have a smaller vertical component of velocity at impact.

The second projectile, launched horizontally, will have no vertical component of velocity at impact, so it will hit the ground with the smallest speed of the three projectiles.

Therefore, the first projectile, launched at an angle of 20 degrees above the horizontal, will hit the ground with the largest speed.

It started off so well, realizing that all three have the same KE. But then, after it answered something that wasn't asked (the range), it went on to be obsessed with the vertical component of the velocity.

I decided to challenge its answer.

But they all have the same initial energy in the beginning. Shouldn't they have the same energy at the bottom when they hit the ground?

You're correct that all three projectiles have the same initial kinetic energy, and conservation of energy tells us that the total energy of the system must be conserved throughout the motion. Therefore, at the bottom of the cliff, all three projectiles will have the same total energy as they did at the top of the cliff.

However, the question specifically asks which projectile hits the ground with the largest speed, not which has the most kinetic energy. The speed of a projectile at any point during its motion depends not only on its kinetic energy but also on its direction and the effects of external forces such as gravity and air resistance.

In the case of these three projectiles, they all have different launch angles, which means they will follow different trajectories and experience different vertical and horizontal components of acceleration due to gravity. These differences will cause the projectiles to hit the ground with different speeds, even though they all have the same initial kinetic energy.

It's a bit puzzling what it is thinking at this point. If they have the same KE in the end, via conservation of energy, then should they also have the same speed?

But kinetic energy is 1/2*m*v^2. If they have the same kinetic energy, they should have the same speed.

Yes, you are correct that the kinetic energy of an object is given by the formula KE = 1/2 * m * v^2, where m is the mass of the object and v is its velocity. If three projectiles of the same mass are launched from the top of a cliff with the same initial speed, they will all have the same initial kinetic energy, and therefore the same total energy throughout their motion.
 

However, as the projectiles follow their different trajectories, they will experience different amounts of air resistance and vertical and horizontal components of acceleration due to gravity. These differences in the forces acting on the projectiles will affect their velocities as they reach the ground.
The projectile launched horizontally will experience no vertical acceleration due to gravity, so it will not gain any speed in the vertical direction as it falls, only in the horizontal direction. The first and third projectiles, on the other hand, will experience significant vertical accelerations due to gravity, which will affect their speeds at impact.
 

Therefore, even though all three projectiles have the same initial kinetic energy, the projectile launched at an angle of 20 degrees above the horizontal will hit the ground with the largest speed due to the combination of its initial horizontal velocity and the vertical velocity gained as it falls.

How can the projectile launched horizontally not experience vertically acceleration due to gravity? After all, it is falling to the ground!

You are correct that a projectile launched horizontally will experience vertical acceleration due to gravity, and it will also fall to the ground just like the other two projectiles.

What I meant to say is that the horizontal component of the velocity of the projectile launched horizontally will remain constant throughout its motion, since there are no external forces acting on it in the horizontal direction. This means that the horizontal velocity of the projectile will be the same at the top of the cliff and at the moment it hits the ground.

However, the vertical component of the velocity of the projectile launched horizontally will increase due to the acceleration of gravity. At the top of the cliff, the vertical component of the velocity is zero, but as the projectile falls, the vertical velocity will increase, and the projectile will hit the ground with a non-zero vertical speed.
 

Therefore, while the horizontal velocity of the horizontally launched projectile remains constant, the vertical component of its velocity will increase due to gravity, resulting in a non-zero speed at impact. However, since the horizontal velocity of the projectile remains constant, it will hit the ground with the smallest speed of the three projectiles.
 

The question asks about the speed, not the velocity. All three gain in speed as it falls to the ground. If their kinetic energy is the same, their speeds must be the same.

You are correct that the question asks about the speed of the projectiles, not the velocity. The speed of an object is the magnitude of its velocity, and it is calculated by taking the absolute value of its velocity vector.
 

If all three projectiles have the same initial kinetic energy, then they must have the same initial speed. As the projectiles fall, they will gain speed due to the force of gravity.
 

Therefore, at the moment of impact, all three projectiles will have the same kinetic energy, which means they will have the same speed. The angle at which the projectiles are launched and the resulting trajectories they follow may affect their final velocities, but their final speeds will be the same since they all have the same kinetic energy at impact.

So, to answer the original question, all three projectiles will hit the ground with the same speed, even though they were launched at different angles.

Phew!! That felt like pulling teeth!

It was as if it doesn't know the difference between speed and velocity, and I'm wondering if it was arguing with me about the vertical component of the velocity. It still makes no sense because clearly I explicitly mentioned "speed" at the very beginning.

Once again, if you don't know what you are looking for, there is no guarantee that you'll get the correct answer and consistent explanation.

Zz.

ChatGPT and Projectile Motion

In my previous post, I mentioned an exercise that I often give to my General Physics students that are learning about projectile motion. Using a PhET application, they found out that two different scenarios produced a projectile motion that has the same maximum height and same time of flight. I asked the students to figure out why.

I decided to post the same question to ChatGPT. The result was a bit of an eye-opener. I will show my question (in red) and its response below:

Why does a projectile shot with initial velocity of 20 m/s and angle 30 degrees with respect to the horizontal reach the same height as the projectile shot with initial velocity of 10 m/s and angle 90 degrees?

The key to understanding this phenomenon is to recognize that the vertical motion of the projectile is independent of its horizontal motion.
For both projectiles, the initial vertical velocity is zero. The only force acting on the projectile in the vertical direction is gravity, which causes the projectile to accelerate downward at a rate of 9.8 m/s^2. The vertical displacement of the projectile can be determined using the formula:
Δy = v0y*t + (1/2)at^2
where Δy is the vertical displacement, v0y is the initial vertical velocity, a is the acceleration due to gravity, and t is the time elapsed.
Since the projectile that was shot with an initial velocity of 10 m/s at an angle of 90 degrees goes straight up, it reaches its maximum height when its vertical velocity becomes zero. At this point, the time elapsed is given by:
t = v0y/a
where v0y is the initial vertical velocity. Substituting in the values, we get:
t = (10 m/s) / (9.8 m/s^2) = 1.02 s
Using this value of t in the above formula, we get:
Δy = (0 m/s)(1.02 s) + (1/2)(9.8 m/s^2)*(1.02 s)^2 = 5.1 m
So, the projectile reaches a maximum height of 5.1 m before falling back down to the ground.
For the projectile that was shot with an initial velocity of 20 m/s at an angle of 30 degrees, we can break down its initial velocity into its horizontal and vertical components:
v0x = v0cos(30) = 17.3 m/s
v0y = v0sin(30) = 10 m/s
The horizontal motion of the projectile is uniform, meaning it moves with a constant velocity of 17.3 m/s. The time taken for the projectile to reach its maximum height is the same as the time taken for it to reach half the range of its motion (i.e., the distance it travels horizontally before hitting the ground). The formula for the time of flight is:
t = 2*v0y/a
Substituting in the values, we get:
t = (2*10 m/s) / (9.8 m/s^2) = 2.04 s
The horizontal distance traveled by the projectile can be calculated using the formula:
R = v0x*t
Substituting in the values, we get:
R = (17.3 m/s)*(2.04 s) = 35.3 m
The maximum height reached by the projectile can be determined using the formula for vertical displacement:
Δy = v0y*t + (1/2)at^2
Substituting in the values, we get:
Δy = (10 m/s)(2.04 s) + (1/2)(9.8 m/s^2)*(2.04 s)^2 = 5.1 m
So, the projectile that was shot with an initial velocity of 20 m/s at an angle of 30 degrees reaches the same maximum height of 5.1 m as the projectile that was shot with an initial velocity of 10 m/s at an angle of 90 degrees, despite traveling much farther horizontally before hitting the ground.

Now, the answer is correct. In fact, it gave me more than what I asked for, i.e. it included the actual calculation of even the range, which I did not ask for.

However, its starting point is incorrect, and in fact, it is self-contradictory. It starts of by saying that the initial vertical velocity for both projectile is ZERO. This is clearly wrong.

Yet, a few lines down, it then mentioned and even found the vertical component of the initial vertical velocity, all while it was oblivious to what it just said in the beginning. So while the answer in the end may be correct, the reasoning, if we were to go by what it said, is puzzling and inconsistent.

I decided to challenge it by pointing out its mistake:

You are mistaken about the initial vertical velocity being zero. For both projectiles, the initial vertical velocity is not zero.

You are correct, I apologize for the mistake. The initial vertical velocity for the projectile shot with an initial velocity of 20 m/s and angle 30 degrees with respect to the horizontal is:
$v_{0y} = v_0 \sin \theta = 20 \text{ m/s} \sin 30^\circ = 10 \text{ m/s}$
And the initial vertical velocity for the projectile shot with an initial velocity of 10 m/s and angle 90 degrees with respect to the horizontal is:
$v_{0y} = v_0 \sin \theta = 10 \text{ m/s} \sin 90^\circ = 10 \text{ m/s}$
So, both projectiles have an initial vertical velocity of 10 m/s. The rest of the explanation and calculations remain the same.

This is now correct. Unfortunately, it requires someone who actually understands projectile motion to spot this. A student learning about it may not notice the inconsistency of the reasoning.

This seems to be the most common issue that I've come across and read about as far as scientific questions being asked to ChatGPT. This was similarly observed in another post that I wrote about. ChatGPT response has correct parts, but there are also parts that are puzzling, contradictory, and often downright wrong, all within one response.

There's more. In my next blog on ChatGPT, I asked it about buoyant forces. You don't want to miss that!

Zz.

My Favorite Web Applications - Part 7

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

My favorite web application - Part 6

This one is an obvious one. It is from PhET, and it is on projectile motion (the "Lab" option).

I have used this web app in many different situations and for many different purposes, including using it as a virtual lab when we went remote. However, even in my face-to-face classes, I continue to use this during our lessons on projectile motion.

One of the most difficult concepts for students to understand with projectile motion is that the maximum height and the time-of-flight of the projectile depends only on the vertical component of the motion. If the vertical component of the motion remains the same, then regardless of what the horizontal component is doing, the maximum height and time-of-flight will be the same as well.

What I typically have the student do with the app is the following:

• Set the canon to an angle of 30 degrees with respect to the horizontal and an initial speed of 20 m/s.
• Fire away!
• Measure the maximum height and the time of flight using the tools available in the app.
• Then change the angle to 90 degrees and an initial speed of 10 m/s.
• Fire away!
• Again, measure the maximum height and time of flight.
• Compare the two situations.

The students will find that for these two different situations, the maximum height and the time of flight are the same. I ask them to discuss this with their partner/s and figure out why these values come out this way. Then I ask them to find another angle and initial speed where the projectile gets to the same height and has the same time of flight.

Of course, the reason for this is that the vertical component of the initial velocity is the same for both situations. The is the only thing that the two motion has in common. Thus, since the maximum height and time of flight depends only on the vertical motion, the two different situations will naturally produce the same values for each of those two quantities. If they understand this, then they will be able to quickly find another angle and initial speed via simple calculation rather than by trial-and-error.

BTW, watch this space as I will be posting a link to an upcoming blog post of my interaction with ChatGPT on this same question that I ask my students.

Edit: This is my blog post on what happened when I asked this projectile motion question to ChatGPT.

Zz.

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.

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.

My Favorite Web Applications - Part 2

 Previous posts:

My favorite web applications - Part 1

It is rather appropriate that the next web application on my list can actually make full use of the vector calculator that I mentioned in a recent post. Many of you may be familiar with the force table in a General Physics course lab. It is a contraption that looks similar to the picture below.

It actually is a rather useful apparatus to demonstrate vector addition and the powerful and convenient method of vector addition using components. Of course, when I assigned this to my students, we didn't use any vector calculator. The students had to calculate the components and find the resultant vector themselves. But this was also the situation where the students encountered the issue with knowing the correct angle that I mention in the vector calculator post. The only difference being that the visual "obviousness" here is more apparent than just looking at the numbers on an Excel spreadsheet.

When we went remote, I was lucky enough to come across this website that had a virtual version of the force table. In fact, other than not having the students struggle with knowing what weights to use, where to clamp them, and how to set up the pulleys, this exercise is quite similar to what I would normally do in class. I had to do only minor rewrite to my lab instruction to incorporate this web exercise.

The one thing I like about this app is that the situation is different for each student, i.e. the magnitudes and directions are unique to each student. Therefore, while they can consult with each other, each student still has to do his/her own calculations to get the answer. The students are given the instruction that they need to do this until they get it right, even if they exhausted all the tries and have to get the web to regenerate brand new set of forces and angles. Once they get it right, they have to do a screen capture of the acknowledgement page, and paste that in the report along with the working done to arrive at the correct answer.

The only thing I wish this web app has is the ability to specify the number of weights (or vectors) in use. In my in-person lab, I had the students start with just one vector, and they have to construct an opposing vector to get the equilibrium condition (trivial, of course, but you'd be surprised at the number of students who had to think about how to do this). Then they move on to having 2 given vectors, and finally 3 vectors, which is what we have in the web app. By doing this gradually, the students realize that they first need to find the resultant vector, and once they have that, all they need to do to get the equilibrium condition is to create another vector of equal magnitude but in opposite direction to the resultant.

Nevertheless, this is a useful web app and something that I intend to use even for in-person instruction.

Zz.

Media Reporting Failed Basic Central Force Motion Mechanics

This news report on The Telegraph written by Joe Pinkstone about the James Webb Space Telescope reaching its final position has a basic flaw that should be easily spotted by any intro physics student who has understood basic central force/circular motion topic.

It will stay at its current position, Lagrange 2 (L2), for its entire operational lifespan, which is expected to be around 20 years. L2 is a gravitational stable point on the other side of the Earth from the Sun, where the pull of the two bodies cancels out.

No, the pull due to the Earth and the Sun does NOT "cancels out", because if it does, then there is no centripetal force to keep the telescope to orbit around the sun! 

Rather, this is the location where the sum of the gravitational forces from the Sun and the Earth provides just the right centripetal force to keep the telescope in orbit around the Sun at the same angular speed as the Earth. It will always be on the opposite side from the Sun with respect to the Earth. You can read more explanation on what is this Lagrange2 (L2) point at the NASA website here.

This is the type of mistake that we expect to see in General Physics classes, not in major news media.

Zz.

Simple Electric Motor Experiment

This was the last lab that my students managed to do before all in-person classes were cancelled due to the coronavirus. They had to build a simple electric motor, making use of the concept of magnetic field created by a loop of wire, the concept of magnetic moment, and magnetic torque.

The final "proof" that they had successfully built the motor is to show that it will spin continuously, which looks like this:

It's a common experiment done in many General Physics labs, but it is still a cool exercise. The students certainly had fun doing it and they felt a sense of accomplishment when they see the spinning coil in motion.

I was just glad we managed to do it just before the shutdown.

Zz.

The Geekiest T-Shirt That I've Ever Bought

I just had to get this one. I found this last week during the members night at Chicago's Adler Planetarium.

The people that I were with of course knew that this is referring to "force", but they didn't get the connection. So I had to explain to them that Newton's 2nd law, i.e. F=ma can be expressed in a more general form, i.e. F = dp/dt, where p is momentum mv. Thus

F = d/dt (mv)

Of course, I'm not surprised that most people, and probably most of Adler's visitors, would not get this unless they know a bit of calculus and have done general physics with calculus. Maybe that was why this t-shirt was on sale! :)

Maybe I'll wear this when I teach kinematics this Fall!

Zz.

Self-Propulsion of Inverse Leidenfrost Droplets Explained

I was not familiar at all with the Leidenfrost effect, even though I've heard the name. So when I read the article, I was fascinated by it. Unlike other people who want find the answers to the mysteries of the universe, etc... I went into physics because I was more curious about these small, little puzzles that, in the end, could have big impact and big outcome elsewhere. So thie Leidenfrost levitation phenomenon is right up my alley, and I'm kicking myself for not reading up on it sooner than this (or maybe they mentioned it in my advanced classical mechanics graduate course, and I overlooked it).

Anyhow, it appears that there is an inverse Leidenfrost self-propulsion, and a group of physicsts have managed to provide an explanation for it. the article describes both the Leidenfrost and inverse Leidenfrost propulsion, so you may read it for yourself. The research work[1], unfortunately, is currently available only via subscription. So you either need one for yourself, or log in to an organization that has site-wide access to it.

And look at the possible application for this seemingly mundane effect that grew out of a basic curiosity:

Gauthier’s team believe the effect could be used to develop efficient techniques for freezing and transporting biological materials including cells and proteins. With the help of simulations, they hope that this transport could occur with no risk of contamination or heat degradation to the materials.

Zz.

[1] A. Gauthier et al. PNAS v.116, p.1174 (2019) https://www.pnas.org/content/116/4/1174

Want To Located The Accelerometer In Your Smartphone?

Rhett Allain has a simple, fun rotational physics experiment that you can perform on your smartphone to locate the position of the accelerometer in that device, all without opening it.

Your smart phone has a bunch of sensors in it. One of the most common is the accelerometer. It's basically a super tiny mass connected with springs (not actual springs). When the phone accelerates in a particular direction, some of these springs will get compressed in order to make the tiny test mass also accelerate. The accelerometer measures this spring compression and uses that to determine the acceleration of the phone. With that, it will know if it is facing up or down. It also can estimate how far you move and use this along with the camera to find out where real world objects are, using ARKit.

So, we know there is a sensor in the phone—but where is it located? I'm not going to take apart my phone; everyone knows I'll never get it back together after that. Instead, I will find out the location by moving the phone in a circular path. Yes, moving in a circle is a type of acceleration.

I'll let you read the article to know what he did, and what you can do yourself. 

Now, the only thing left is to verify the result. Someone needs to open an iPhone 7 and confirm the location of the accelerometer (do we even know what it looks like in such a device?). Any volunteers? :)

Zz.

Feynman's Lost Lecture

If you didn't buy the book or didn't read about it, here's a take on Feynman's Lost Lecture, presented by a guest on Minute Physics video.



Zz.

That Impossible EM Drive Might Be ..... Impossible After All!

Crackpots were just having a field day when NASA announced several years ago of an EM propulsion that somehow violates momentum conservation laws. Now comes a more careful experiment from a group that tried to reproduce this result, and the outcome is rather hysterical.

The team built their EM drive with the same dimensions as the one that NASA tested, and placed it in a vacuum chamber. Then, they piped microwaves into the cavity and measured its tiny movements using lasers. As in previous tests, they found it produced thrust, as measured by a spring. But when positioned so that the microwaves could not possibly produce thrust in the direction of the spring, the drive seemed to push just as hard.

And, when the team cut the power by half, it barely affected the thrust. So, it seems there’s something else at work. The researchers say the thrust may be produced by an interaction between Earth’s magnetic field and the cables that power the microwave amplifier.

So far, this has only been reported in a conference proceeding, which is linked in the New Scientist article (you will need ResearchGate access).

I'm sure there will be many more tests of this thing soon, but I can't help but chuckle at the apparent conclusion here.

Zz.

Common Mistakes By Students In Intro Physics

Rhett Allain has listed 3 common mistakes and misunderstanding done by student in intro kinematics physics courses.

I kinda agree with all of them, and I've seen them myself. In fact, when I teach "F=ma" and try to impress upon them its validity, I will ask them that if it is true, why do you need to keep your foot on the gas pedal to keep the vehicle moving at constant speed while driving? This appears to indicate that "F" produces a constant "speed", and thus, "a=0".

Tackling this is important, because the students already have a set of understanding of how the world around the works, whether correctly or not. It needs to be tackled head-on. I tackled this also in dealing with current where we calculate the drift velocity of conduction electrons. The students discover that the drift velocity is excruciatingly slow. So then I ask them that if the conduction electrons move like molasses, why does it appear that when I turn the switch on, the light comes on almost instantaneously?

Still, if we are nitpicking here, I have a small issue with the first item on Allain's list:

What happens when you have a constant force on an object? A very common student answer is that a constant force on an object will make it move at a constant speed—which is wrong, but it sort of makes sense.

Because he's using "speed" and not "velocity", it opens up a possibility of a special case of a central force, or even a centripetal force, in a circular motion where the object has a net force acting on it, but its speed remains the same. Because the central force is always perpendicular to the motion of the particle, it imparts no increase in speed, just a change in direction. So yes, the velocity changes, but the magnitude of the velocity (the speed) does not. So the misconception here isn't always wrong.

Zz.

Amazon's CAPTCHA Patent Proposal Tests Your Physics Understanding

... well, more like your physics INTUITION on what should happen next.

It seems that Amazon has file a patent application that uses a physics engine to generate scenarios to see if you are a real person or a bot.

The company has filed a patent application for a new CAPTCHA method which would show you a 3D simulation of something about to happen to a person or object. That something would involve Newtonian physics — perhaps an item is about to fall on someone, or a ball is about to roll down a slope. The test would then show you several "after" scenarios and, if you pick the correct option, you've passed the test.
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The idea is that, because you are a human, you have an "intuitive" understanding of what would happen next in these scenarios. But computers need much more information about the scene and "might be unable to solve the test", according to the application.

Definitely interesting, although in Fig. 3B shown in the article, both Fig (A) and Fig (B) might be possible depending on the ambiguity of the drawing.

But this brings me an important point that I've been telling my students in intro physics classes when they dealt with mechanics. We all ALREADY KNOW many of the things that will happen in cases like this. We do not need to learn physics or to be enrolled in a physics class to know the qualitative description of the dynamics of these systems. So we are not teaching you about something you are not familiar with.

What a formal physics lesson will do is to describe these things more accurately, i.e. in a QUANTITATIVE manner. We won't simply say "Oh, the ball will roll down that inclined plane." Rather, we will describe the motion of the ball mathematically, and we will be able to say how long the ball will take to each the bottom, at what speed, etc...etc. In other words, we don't just say "What goes up must come down", but we will also say "When and where it will come down". This is what separates physics (and science) from hand-waving, everyday conversation.

All of us already have an intuitive understanding of the physical systems around us. That's why Amazon can make such a CAPTCHA test for everyone. A physics lessons simply formalize that understanding in a more accurate and non-ambiguous fashion.

Zz.

The Physics of Texting And Driving

First of all, let me be clear on this. I hate, HATE, HATE drivers who play with their mobile devices while they drive. I don't care if it is texting (stupid!) or just talking on their phones. These drivers are often driving erratically, unpredictably, and often do not use turn signals, etc. They are distracted drivers, and their stupid acts put my life and my safety in jeopardy. My nasty thought on this is that I wish Darwin would eliminate them out of the gene pool.

There! I feel better now. Coming back to the more sedate and sensible topic related to physics, Rhett Allain has a nice, short article on why physics will rationally explain to you why texting and driving is not safe, and why texting and driving ANNOYS OTHER PEOPLE!

OK, so my calmness didn't last very long.

The physics is quite elementary that even any high-school physics students can understand. And now, I am going back to my happy place.

Zz.

The Brachistochrone Problem

There are many sources that describes this problem. Mary Boas also devoted a substantial portion of it in her classic text "Mathematical Methods in the Physical Sciences". Here, Rhett Allain describes it once more in his Wired article.

Laymen might find it fascinating just to know the shape of the path, while physics students might find it useful especially if you're just about to take class in Least Action principle.

Zz.

Will You Be Doing This Physics Demo For Your Students?

I like my students, and I love physics demos, but I don't think I'll be doing THIS physics demo anytime soon, thankyouverymuch!



It is a neat effect, and if someone else performed this, the media would have proclaimed this as "defying the laws of physics".

Maybe I can do a demo on this on a smaller scale, perhaps  using a Barbie doll. And if you ask me how in the world I have a Barbie doll in my possession, I'll send my GI Joe to capture you!

Zz.

The Physics of Car Crashes

I hope you never have to figure out the physics in this context, but it is still a nice scenario in basic mechanics.



Zz.