Dot Physics

Rarely am I up late enough to watch the Colbert Report, but by chance I saw it last night. I know Stephen Colbert is a big fan of Dot Physics, and so this is a message to him. Stevie, good job. Here is what he said during his show on the “The Word” segment. Just to give you the context, he was making some point about how if you say anything while talking like a hippie, you make what you said untrue:

Colbert: “Net force of the object equals mass times acceleration, MAN. There. I completely invalidated Newton’s second law of motion.”

First, the good. He said “net force”. How many times do people talk about Newton’s second law and say “F = ma”? Not a very good way to say it. Net force is extremely important in that expression.

Now for the bad. Colbert said “net force of the object”. Really, he should have said “the net force ON the object”. Perhaps Colbert accepts the common idea that force is a property of an object like its energy. Instead, force is an interaction between two objects. Stephen, might I direct you to my post “What is a Force”?

Colbert made one other slight mistake. He did not mention the vector nature of Newton’s second law. I am still quite happy that he said “net force”.

Big trucks are not as popular as they used to be, but gas prices are going down so maybe this commercial for the ford F-150 will start showing up again:

They say its a real demonstration, but it has seemed odd to me. (they also say this is a professional driver on a closed course and don’t try this at home - damn! I was SO going to do that this weekend). Here is my analysis:

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This must have been mentioned in a previous post, but I am too lazy to search. Anyway, I think have enough stuff here (at blog.dotphys.net) to finish moving stuff from my previous version of the blog. What does this mean and why do you care? You care because if you are one of the two people that read these old posts (I am one of the two) then you will see them again.

Atwood’s machine is the name of a device that looks like this:

Also known as “two masses on a pulley”. Surprisingly, this simple device comes up a lot in intro physics texts. It also brings up some interesting issues. I will go over the basic way to solve a problem like this (as an example) and then talk about the other interesting issues it brings up.

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Here is a video of a guy jumping 35 feet into a pool of water only 1 foot deep.

UPDATE: Apparently, that video went away. Here is another version.

How does this work?

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Numerical calculations are grand. Of course, they are just another form of normal calculations - like I have said before. So, I have mostly used VPython for my calculations on my posts. But there is a new game in town: Easy Java Simulations. What is the difference between these two? Which is better for students? Which is better for me? What are their strengths? What other questions are there? What other questions are there?

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In part I of this post, I struggled to show that a particle in an infinite well can only exist at certain energies. If you try to put a particle with more than one energy, the probability oscillates at a frequency (E₂ - E₁)/h. So, what is next? Well I think I am ready to attack the photon.

According to the ultimate source of truthiness (wikipedia), the photon is the elementary particle responsible for the electromagnetic interaction. In general, the photon is view as the particle manifestation of light where light can exhibit both particle and wave properties.

Before I go too far, I would like to mention a good summary paper of this problem from David Norwood. - “The Use and Abuse of the “Photon” in Nanomechanics” (pdf)

I have said it before, and I will say it again. Science is all about models. In this case, there is a model for light that says it can be particle or wave. This model is not needed. Almost all of the stuff you think is an example of the particle property of light can be explained with the quantum nature of matter. I think the following sums this up well. The photon model for light uses the following relationship:

Where E is the energy of the “photon”, h is Planck’s constant and the greek letter nu (looks like a v) stands for the frequency of the light. There is a relationship like this, but it would be better to write it as:

Where nu is the frequency of the light (or the frequency of the changes in potential for a particle - it actually doesn’t have to be light). Delta E is the change in energy between two energy levels in a quantized system. h is still Planck’s constant.

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One of the fundamental aspects of physics is the study of light and how that interacts with matter. I have been putting off this post - mainly because I am not a quantum mechanic (I am a classical mechanic). There are lots of things that could be done in this post, but I am going to try and keep it limited (and maybe come back to the interesting points later). Also, most of my posts are aimed at the intro-college level or advanced high school level. This will be a little higher. If you are in high school, there is still a lot of stuff for you here.

Let me summarize where I am going to take this post. I am going to try and briefly describe the quantum nature of matter. I am then going to show how this relates to light. In the end, I will show that the common idea that light has a dual wave-particle nature is not a necessary model. Just about everything that normal physicists (especially undergraduates) look at can be explained with light as a wave.

One final point. I am not really that knowledgeable in this area (especially compared to some). I did not “figure” this stuff out. Instead, I am repeating the arguments that David Norwood proposed after he summarized the arguments of others.

Now on with the fun.

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On MythBusters this week, Adam and Jamie tested the bullet-proofness of various objects. The one that sticks in my mind is the ipod. The said there was a report of a solider being shot by an AK-47, but he was saved because the bullet hit his ipod. To test this, Adam shot an AK-47 at an ipod and it went through. Their conclusion was that he was also wearing body armor. I am not sure I like that conclusion. Why would someone report that the ipod saved him if he was also wearing body armor? Maybe they would, but not sure.

I was thinking, maybe the bullet went through the ipod because they were only 10 feet away. Maybe this doesn’t really matter - but how would I know? This is a great example to look at numerical calculations involving air resistance.

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I just watched two episodes of the discovery show Time Warp. Really an interesting show. There are many videos that I could see some analysis project for (too bad I am like 20 projects behind schedule - I think of things faster than I can do them). There is one problem though. It seems like all of the people on the show like to use physics terms, but they use them incorrectly. This DRIVES ME NUTS. You can’t have “energy going this way”. Energy is a scalar, not a vector. You can’t have “force flowing through this”. You can’t “put a lot of force in it”. I know, I know… I should lighten up. These phrases all makes sense in common-speak. But what are they really trying to say when they say these things? They end up just sounding “sciency”, but wrong.

Ok, enough of the negativity (although, I am pretty good at it). Here are some things I would like to explore:

• Conservation of momentum for colliding pool balls.
• Torque and friction for a spinning (but not rolling) pool ball.
• Crazy jumping guy landing after jumping 25 feet down. Show that by increasing the distance of the land, he decreases the force (work-energy).
• Crazy jumping guy running sideways on a wall. Show that circular acceleration creates a force between him and the wall that also leads to friction.
• Crazy-think-he-is-a-samurai guy pushes back and down on another guy’s head to make him sit down.
• Crazy-think-he-is-a-samurai guy does “short punch” to push other guy back.

So, you see, I will be busy. I have to first capture these clips so I can analyze them, then do the analysis.