Learning Physics?

[Scott Shepherd]

Greetings all :)

I have a niece that's taking physics in college starting this semester and I'm often the one that gets the phone call when she doesn't understand things. Not sure why, because she's farther along in her education than I ever made it, but none the less, the little I know about physics, I do not it's not an easy subject.

So I thought I'd secretly brush up on it (okay, learn it for the first time) if I could, but hopefully casually from the comfort of my chair, and better yet, as close to free as possible, since I have no need to learn it, other than to be able to help her when she needs help.

Any good online sources for teaching some of the basics of physics. I'm not opposed to buying a book or a few things if needed, but not looking to enroll in a class or spend 100's of dollars.

Any suggestions?

Thanks!

[Mike Henderson]

The best source I've found is the Feynman "Lectures on Physics (http://www.amazon.com/Feynman-Lectures-Physics-Set/dp/0201021153/ref=sr_1_1?s=books&ie=UTF8&qid=1283097441&sr=1-1)". It's a series of three books and shows Feynman's unique style of teaching. He prepared the lectures for the freshman class in Physics at CalTech.

Not an "easy" read but tailored to a freshman level and comprehensive. Physics, like engineering, is really almost all mathematics.

Mike

[Mitchell Andrus]

You could visit your local college bookstore, or...

http://www.amazon.com/Physics-Dummies-Steve-Holzner/dp/0764554336

Ah.... Snells' Law.....
.

[Bryan Rocker]

One quick question on the "physics" class. Having taken college level physics, is this the algebra based course or the calculus based course? The difference between the two can be pretty significant when it comes to the math required......

[Jim Koepke]

Physics is the study of matter, forces and the effects they have on eachother and everything.

Things like:

Motion and Newton's laws of motion.

Directions of motion and force.

Things like pressure and torque.

The atomic nature of mater.

The 4 states of matter, solid, liquid, gas and plasma.

Heat, its transmission and changes of state.

Sound and sound waves.

Electricity and its relationship with magnetism.

Then there was light at the end of the tunnel. (sorry just can't resist)

Then there is Nuclear Physics.

And the study of relativity will have you saying things like:

There was a young woman named Bright.
Who traveled much faster than light.
She left one day,
In a relative way,
And returned on the previous night.

jim

[Ken Garlock]

The best source I've found is the Feynman "Lectures on Physics (http://www.amazon.com/Feynman-Lectures-Physics-Set/dp/0201021153/ref=sr_1_1?s=books&ie=UTF8&qid=1283097441&sr=1-1)". It's a series of three books and shows Feynman's unique style of teaching. He prepared the lectures for the freshman class in Physics at CalTech.

Not an "easy" read but tailored to a freshman level and comprehensive. Physics, like engineering, is really almost all mathematics.

Mike

Good afternoon, Mike.

Let me recommend "Surely You're Joking Mr. Feynman" It is light reading and very funny in places.

A follow-on is "What Do You Care What Other People Think?"

E**(Pi*i) +1 = 0

[Mike Henderson]

One quick question on the "physics" class. Having taken college level physics, is this the algebra based course or the calculus based course? The difference between the two can be pretty significant when it comes to the math required......
I don't know how you'd do college level physics without calculus. I wrote a paper a while back on differential equations (http://members.cox.net/mnh-overflow/Differential_%20Equations.pdf), oriented towards high school students. For those who need a refresher, take a look.

Also, a companion paper on logarithms (http://members.cox.net/michael.henderson/Papers/Logarithms.pdf).

Both papers are targeted at high school students who are planning to go to college for engineering, physics, or mathematics.

Mike

[If you have a high school student heading to college for a technical field, give him or her a copy of these papers.]

[Stephen Tashiro]

There is an interesting series of DVDs (sold on Amazon and probably other places) by Jason Gibson. They simply show him standing in front of a marker board working problems. He concentrates on the "crank turning" type of problem. I've only watched two of his math DVDs. I judge them to be useful to students. He isn't strong on conveying a deep understanding of the material, but if you are getting questions about how to work problems, I predict that you (and the student) would find his DVDs useful. He has several DVDs on topics in physics.

There are also DVDs by a troup of actors called "The Standard Deviants" that are lighter fare. They mix the academic material with brief nonsensical skits. Jason's DVDs offer repetitive drill on topics. The "Deviants" give topics the brief once-over.

[Mitchell Andrus]

There was a young woman named Bright.
Who traveled much faster than light.
She left one day,
In a relative way,
And returned on the previous night.



So... if she arrives before she leaves (she would be plural) and keeps herself from traveling, would she then vanish leaving herself 'singlular' again?

I feel a Star Trek episode coming on....
.

[Mitchell Andrus]

So... if she arrives before she leaves (she would be plural) and keeps herself from traveling, would she then vanish leaving herself 'singlular' again?

.

Ouch, there's that headache again.
.

[Dan Hintz]

Steve,

I have found the HyperPhysics pages to be a nice refresher for some of the more common stuff. Google usually turns up the proper page as it's not always easy to find from their main site:
http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html

And the two Feynmen books Ken suggests are fun reads (have them both on my shelves)... a few redundant stories between the two, told from slightly different viewpoints of time, with the "What do you care" book being a bit more touchy-feely than the first.

[Scott Shepherd]

Okay, on second thoughts, how about I just tell her to call one of you? :)

I love to learn, but this sounds like it's about 3 levels over my head from the get go.

[Bob Coleman]

I second the hyperphysics website. And for help with math, check out http://tutorial.math.lamar.edu/ The guy basically has a book for the fist two years of college level math posted.

[Kent E. Matthew]

I picked up the book Physics Demystified. Good luck because I hit the stone wall rather early.

[John Coloccia]

I don't know how you'd do college level physics without calculus.

Mike, I agree 100%, but the fact is that they DO teach physics in college without ever once touching calculus. It's easy. You memorize a bunch of formula's and then you fill in the blanks. Of course, you'll get the wrong answers half the time, like when they completely ignore the rotational inertia of a marble rolling down an incline. :rolleyes:

Physics really makes no sense until you teach it with a differential equations approach, and I've always felt that you should not go anywhere near Physics your first three semesters. You should do CalcI, CalcII, DiffEqs and THEN do basic mechanics. Sadly, this isn't how it's done and it's really too bad. I guess the reasoning is that most students won't ever take DiffEqs but they still should know some physics, but my feeling is "What the heck is the point?". Instead, they should have physics lectures where you don't calculate anything at all. It wouldn't be "Physics I". Maybe they'd call it "General Science I". You just sit there and listen and discuss basic physics concepts with your professor. That would be far more useful than calculating the velocity of a pendulum or the tension on a rope by manipulating equations around.

Scott: I don't have a specific reference, but what you want to search on is "Physics Basic Mechanics" or kinematics. She'll probably be doing things like blocks sliding down a plane, pendulums, tension on a rope, launching balls out of canons, etc. There's so many videos and tutorials out there these days that it's difficult to narrow it down to just one source.

[Dan Hintz]

It depends on if you're teaching the concepts of physics or the quantitative values... the concepts need zero math, only a good teacher (getting harder to find these days), and as such the concepts are rarely understood these days.

I've taken a pretty wide array of courses in my student career... advanced differential equations, lots of organic chemistry, thermodynamics (taught by a real meanie), optics, and my specialization for my Masters was digital communications and signal processing (probability math that gave me nightmares). How much of it do I use in my job? Zero! I was a solid C student in high school when it came to math, so it's ironic I chose one of the most math-intensive specializations, no? I learned to concentrate on the concepts of the subject rather than the math behind it... to Mike's point, the math itself was (is?) secondary, IMO. It's cranking numbers through a pre-determined formula, you're not there to recreate it, only to understand why it exists.

I could have seriously used some tutors back then to help me through the rough spots (though that may have been due more to my lack of patience and desire to actually study!). If I had to do college again, I may have chosen a course of mathematics that was a little more conceptual in nature... like topology or other multi-dimensional maths.

[Scott Shepherd]

Okay, I'm convinced y'all are just making words up now :D

[Ken Fitzgerald]

Okay, I'm convinced y'all are just making words up now :D

I wondered how long it would take you to catch on.....:rolleyes::D

[Scott Shepherd]

Apparently 16 posts :) About 5 times as many licks at it takes to get to the center or a tootsie pop :) Ahhhh...1.........2.........3 - 3!

[Dan Hintz]

Oh, I'll also add that the Schaum's guides found at any major book store are also somewhat decent, if for no other reason than to show a wider array of similar problems with worked solutions.

What sorts of physics is she taking? I'm going to guess statics as dynamics are usually taught as a second course. I have a notebook of solved problems from my own physics days (neatly laid out on Engineering paper... nerd alert!), but I'm leery about handing that to any fresh student for fear they might use it as too much of a crutch rather than learning the concepts themselves. But I'd be willing to share if you think it would help...

[brian corwin]

Hello,
In terms of a "free" way to brush up on physics I would highly recommend you check out OCW over at MIT via the following link

http://ocw.mit.edu/courses/physics/

They have pdfs of lecture notes and videos freely available from many courses and for numerous years.

It is truly an amazing resource. I have turned to the notes on some of the higher level graduate courses several times.

Edit: for added info. Some of the years are less useful than the others.

B

[Mike Henderson]

Okay, I'll post a physics thought question that's been bothering me.

Suppose you have a laser which will output a single frequency of light (very narrow bandwidth). You put a beamsplitter in the path of the beam and divert the two resulting beams into separate paths that are one half wavelength different in length. Then you re-combine the beams. Because they are a half wavelength out of phase, the two beams cancel each other out when the resulting beam is projected on a surface.

Question: Since energy can neither be created nor destroyed, where did the energy in the initial beam go?

Mike

[Ken Garlock]

Ok Mike, I'll show my stupidity as follows:

Entropy will rain supreme.
The photons, since they are packets of energy, will be converted to heat.

[Don Orr]

A professor of Physics at Union College here in Schenectady, NY wrote a book called "How to Teach Physics to Your Dog". I have not read or even seen it, but it sounds like fun.:confused::rolleyes:;)

[Dan Hintz]

Mike,

Your supposition is flawed, hence your question is moot. The beam is not completely canceled, and in fact you will see a series of podal/anti-podal points (interference pattern) on the screen. Light has a somewhat unique ability to be viewed both as a continuous function and a quantized value, so answering questions like that get tricky, particularly for those not studying the field. In this case, though, I think it's the quantized part that holds the most value here.

If you consider the passing light as quantized values, I think you'll begin to see why it's not the same answer as if the two combining waves had "values" of energy everywhere

[John Coloccia]

You can't make an arrangement where two "beams" perfectly destructive interfere. There will always be constructive interference with any real experiment once everything is taken into account, and that will be just enough to conserve energy. In the case of one photon interfering with itself, you have to analyze this by following the evolution of the photon's wave function. You'll find that nothing is destroyed at all but there are simply places on the screen where the photon usually goes, sometimes goes and never goes.

[Chris Padilla]

E**(Pi*i) +1 = 0

We EEs like to use a 'j' to represent sqrt(-1). :)

Euler:

exp(+/- jtheta) = cos theta +/- j sin theta

[Ken Fitzgerald]

Chris...IIRC....Ken is a EE 2.

[Mike Henderson]

Okay, let me pose it a different way. Suppose you were receiving an electromagnetic signal (maybe over a wire pair) at a modest frequency, say 1000Hz. At the receiver, you detect that signal and determine the amplitude, frequency and phase. The received frequency is very stable and it's just this one frequency (remember, this is a thought experiment so real world issues like frequency stability do not apply).

You measure the amplitude, frequency and phase of the received signal and then you generate a signal of the exact same amplitude and frequency but 180 degrees out of phase and inject it at the input of your receiver.

Your receiver will now show no signal received.

Where did the energy go?

Mike

[While it is done mathematically in a modem, this is the way echo cancellation works in modems. But the mathematics is just another way of expressing the real world. You really could inject a physical signal and you would see the exact same results. It's just a lot easier to do it mathematically (using signal processing).]

[Ken Fitzgerald]

They cancel each other.

[Mike Henderson]

They cancel each other.
The two signals do cancel each other, but the both contain energy. Where does that energy go?

Mike

[Ken Fitzgerald]

Let's get into waveguide theory......

Maybe super-con magnets and quantum physics?

[Dan Hintz]

Mike,

Let me pose another question in the same vein...

What if I connect a resistor across the terminals of a 9V battery, but neither is connected to ground... what's the voltage at each terminal? The question you need to ask in return is "In reference to what?".

Now, take a look at a simple 1/4 wave pole... what's the voltage at the tip at any one moment in time? Think of the same return question.

Now add in that inverse phase signal... what happens? The energy doesn't magically disappear...

[Ken Fitzgerald]

The two signals do cancel each other, but the both contain energy. Where does that energy go?

Mike

I would suggest it turns to heat but I could be wrong.

[Scott Shepherd]

Now add in that inverse phase signal... what happens? The energy doesn't magically disappear...

Does so :p

[Ken Fitzgerald]

Mike,

Let me pose another question in the same vein...

What if I connect a resistor across the terminals of a 9V battery, but neither is connected to ground... what's the voltage at each terminal? The question you need to ask in return is "In reference to what?".

Now, take a look at a simple 1/4 wave pole... what's the voltage at the tip at any one moment in time? Think of the same return question.

Now add in that inverse phase signal... what happens? The energy doesn't magically disappear...

I would suggest as long as the resistor isn't a dead short, the battery terminals are 9 volts dc +/- with respect to the other terminal.

In the case of the 1/4 wave dipole, I'd suggest at any one time, the voltage is 90º out of phase to the other end....could be leading or could be lagging depending on the reference.

[Chris Padilla]

Chris...IIRC....Ken is a EE 2.

Usually, one can tell the origin/background of a electronic's person by whether or not they use 'i' or 'j' for the imaginary number. Most physicists use the 'i'...EEs use a 'j'. :)

[Ken Fitzgerald]

Usually, one can tell the origin/background of a electronic's person by whether or not they use 'i' or 'j' for the imaginary number. Most physicists use the 'i'...EEs use a 'j'. :)

Chris,

I'd sure like to hear both sides of that disagreement argued.:confused:;)

Frankly, it's been so long since I studied that and have never used it......I forget how I was taught.

[Chris Padilla]

The two signals do cancel each other, but the both contain energy. Where does that energy go?

Mike

http://scientopia.org/blogs/skullsinthestars/2010/04/07/wave-interference-where-does-the-energy-go/

[Dan Hintz]

Usually, one can tell the origin/background of a electronic's person by whether or not they use 'i' or 'j' for the imaginary number. Most physicists use the 'i'...EEs use a 'j'. :)
I would say it depends upon what class I'm currently being forced to suffer through ;)

[Dan Hintz]

I would suggest as long as the resistor isn't a dead short, the battery terminals are 9 volts dc +/- with respect to the other terminal.
Yep, but that was just a lead-in...

In the case of the 1/4 wave dipole, I'd suggest at any one time, the voltage is 90º out of phase to the other end....could be leading or could be lagging depending on the reference.
Yep, but again, a lead-in...

More importantly, it is in reference to the ground plane for the antenna (whatever that might be, even if virtual). The point being the voltage swings up/down as the wave impinges upon it. So what happens with a signal 180 degrees out of phase impinges upon it? Do the two waves cancel each other from an energy standpoint? No. So think about what happens to the voltage at the major points of the antenna.

When you start visualizing this stuff, the math begins to appear irrelevant.

[John Coloccia]

Okay, let me pose it a different way. Suppose you were receiving an electromagnetic signal (maybe over a wire pair) at a modest frequency, say 1000Hz. At the receiver, you detect that signal and determine the amplitude, frequency and phase. The received frequency is very stable and it's just this one frequency (remember, this is a thought experiment so real world issues like frequency stability do not apply).

You measure the amplitude, frequency and phase of the received signal and then you generate a signal of the exact same amplitude and frequency but 180 degrees out of phase and inject it at the input of your receiver.

Your receiver will now show no signal received.

Where did the energy go?

Mike

[While it is done mathematically in a modem, this is the way echo cancellation works in modems. But the mathematics is just another way of expressing the real world. You really could inject a physical signal and you would see the exact same results. It's just a lot easier to do it mathematically (using signal processing).]

Ultimately, any "excess" energy gets dissipated as heat because you're wiggling electrons, and they wiggle other electrons and atoms, etc etc.

But I bolded the "thought experiment" part. The reason is, and I mean this will the deepest of respect, is that you're kind of asking "Assuming that the laws of physics don't apply, what do the laws of physics predict?". There's no such thing as a pure anything. This is guaranteed by the uncertainty principle. When you analyze a real problem, you find that the ugly realities of dispersion and other effects will spoil what you're trying to produce, and it will spoil it exactly the right amount to always compensate and conserve.

I hope that makes sense.

[Wayne Watling]

Hi Scott,

Here is one of the best teaching sites on the net and its free. The guy is an amazing teacher.

http://www.khanacademy.org/

http://www.khanacademy.org/#Physics

Regards,
Wayne

[Mike Henderson]

Ultimately, any "excess" energy gets dissipated as heat because you're wiggling electrons, and they wiggle other electrons and atoms, etc etc.

But I bolded the "thought experiment" part. The reason is, and I mean this will the deepest of respect, is that you're kind of asking "Assuming that the laws of physics don't apply, what do the laws of physics predict?". There's no such thing as a pure anything. This is guaranteed by the uncertainty principle. When you analyze a real problem, you find that the ugly realities of dispersion and other effects will spoil what you're trying to produce, and it will spoil it exactly the right amount to always compensate and conserve.

I hope that makes sense.
In physics thought experiments (http://en.wikipedia.org/wiki/Thought_experiment) you're allowed to specify things that would be extremely difficult to produce in real life. The thought experiment is still valid because physics still has to apply even in extreme cases.

Einstein and Feynman (among others) were great proponents of thought experiments. Schrödinger's cat (http://en.wikipedia.org/wiki/Schr%C3%B6dinger's_cat)is a thought experiment.

Mike

[Ed Harrow]

Several possibilities...

Physics Made Simple - Ira Freeman
Physics foor the Utterly Confused - Daniel Oman/Robert Oman
and my personal favorite:
The Cartoon Guide to Physics - Larry Gonick & Art Huffman

I'm not familiar with the websites mentioned - they could well be better.

[John Coloccia]

In physics thought experiments (http://en.wikipedia.org/wiki/Thought_experiment) you're allowed to specify things that would be extremely difficult to produce in real life. The thought experiment is still valid because physics still has to apply even in extreme cases.

Einstein and Feynman (among others) were great proponents of thought experiments. Schrödinger's cat (http://en.wikipedia.org/wiki/Schr%C3%B6dinger's_cat)is a thought experiment.

Mike

Yes, agreed 100%. In this case, though, it's an impossible situation. That impossibility is what insures the conservation laws will hold. It's sort of like saying "what do the laws of physics predict would happen if you could extract path information from the double slit experiment, yet maintain the interference pattern?" The problem is that the situation is impossible within the current framework of the physical laws so the laws don't apply anymore. In your case, setting up the perfect situation is impossible given the current framework, so analyzing it in the same framework gives results that no longer agree with experiment.

The other way of looking at it is that the photon always ends up SOMEWHERE. It never goes poof. When you analyze it on a photon by photon basis, the conservation of energy becomes obvious. The photon goes somewhere. You never end up with no photon. It's only when you analyze it using a wave treatment that you have the problem of purely destructive interference, but then when you do that and take everything into account you find that it's impossible to actually setup a situation that gives you that pure destructive interference. it's not just a matter of technology or "hardness". It's a matter of there's no arrangement that's possible in the current framework that could ever give you that without also giving you enough constructive interference elsewhere to make up for it.

Schrodinger's cat can, in principle, be setup. We can't really do it in real life right now, but presumably that's just a technological hurdle. The case you're trying to setup can't be setup even in principle, no more than a measurement could ever be taken that violates the uncertainty principle. It's deeply unsatisfying, and it was deeply unsatisfying to Einstein and Shrodinger himself as well, but that's all there is at the moment.

BTW, I use this stuff everyday. Whenever my inlays don't fit perfectly, I always blame Heisenburg :D

[Ken Fitzgerald]

And to think....I just came to the Creek to learn to build furniture.....:rolleyes::D

[Dan Hintz]

Someone took my stapler...

[Chuck Saunders]

Maybe drop the thought experiments back a step perhaps

you are traveling in your car at the speed of light, you turn on the headlights, what happens?

[Rich Stewart]

Boy, do I feel stupid.

[Dan Hintz]

you are traveling in your car at the speed of light, you turn on the headlights, what happens?
I blow a fuse because I installed the Taiwanese faster-than-the-speed-of-light bulbs incorrectly...

[Rod Sheridan]

My shop cat has started a collection to save Schrodinger's cat.

Unfortunately all he's collected so far is a bunch of planer shavings and a catnip mouse.......Rod.

P.S. Being in the elctrical field I've always used "j".....

[Ken Fitzgerald]

Rod,

I need an address to make a contribution to your cat's efforts. Will I have to pay import/export fees on shavings going to Canada?

[Rod Sheridan]

Rod,

I need an address to make a contribution to your cat's efforts. Will I have to pay import/export fees on shavings going to Canada?

Ken, no import fees, we're all one happy family now with NAFTA:D

Could I be so bold as to request something other than white oak? I seem to be swimming in that at present.

Good thing that Diann's parents have a farm and their chickens need shavings for bedding.

[John Pratt]

I keep checking back on the updates to this thread because I have a school age children in college and high school. I have come to the conclusion that you guys are keeping this thread going just so I can come to the realization that I:

A. Should have studied more in school.

B. You're doing it just to make me realize how stupid/ignorant I really am.

Keep it up though. You are never to old to learn.

[Dan Hintz]

John,

Some of my favorite days are the ones that include technical discussions in the forums.

[John Pratt]

I agree. It keeps my mind fresh and really makes me want to get out and learn more. When I was in school (high school and college), I wanted to get into physics and organic chemistry. They both really fascinate me to the extent that I thought about a career in one or the other. But the one small detractor was my lack of paitence and desire for math. Unfortunately, you can't eliminate the math from either career. College Calc was mind numbing for me.

[Chris Padilla]

P.S. Being in the elctrical field I've always used "j".....

I always liked you, Rod.... ;)

[Ken Garlock]

I would suggest as long as the resistor isn't a dead short, the battery terminals are 9 volts dc +/- with respect to the other terminal.

In the case of the 1/4 wave dipole, I'd suggest at any one time, the voltage is 90º out of phase to the other end....could be leading or could be lagging depending on the reference.

Well, having built more than one dipole antenna over the years, the 1/4 wave vertical is unique in that it works equally poorly in all directions.:)

If the dipole is constructed in electrical multiples of 1/4 wave every thing is goodness and it radiates energy, and you have a voltage max at the tip of the antenna. Consider a sine wave that is only 90 deg. (You might ask what about the remainder of the sine wave? It's energy is radiated via radials mounted at the bottom of the antenna. Alternatively, the ground absorbs the energy.)

BUT, What if the antenna isn't the correct length? You then have a problem. When the sine wave gets to the end of the antenna, it does not have a max or a min, and it is very unhappy and reflects some amount of the sine wave back to the source. This is expressed as a standing wave in antenna parlance. The EE will talk about +jwt, or -jwt. When jwt =0, everybody is happy and you have a condition known as resonance.

Time to go to the store and maintain domestic tranquility. :):D

[Scott Shepherd]

Thanks for all the suggestions, sites, links, and recommendations!

Just a side note, if you didn't click on Wayne's links, take a minute (or hours) and do so. It's an excellent site teaching just about anything.

Thanks again all!

[Bill Cunningham]

All this reminds me of a trip to the library several years ago and was just poking around at anything that looked interesting.. As I was leaving, the Librarian Said fairly loudly "Mr Cunningham I have that book you ordered" Looking to impress, I said (slightly louder than I should have) Oh you mean Stephen Hawking's, A Brief History of Time ? And she said (just as loudly) NO, Gary Larson, Wiener dog Art.. There were several chuckles, to which I replied See! Now that's a range of reading!

[Chuck Saunders]

My shop cat has started a collection to save Schrodinger's cat.

Unfortunately all he's collected so far is a bunch of planer shavings and a catnip mouse.......Rod.

P.S. Being in the elctrical field I've always used "j".....
Actually, your cat may have raised quite a large sum. The only problem is that when observed the field collapses leaving only the shavings and the security system (catnip mouse)

[Dan Hintz]

Heisenberg may have something to say about that collection... you can count the wood chips, but you won't know where they are afterwards...

[Carl Hunsinger]

Good afternoon, Mike.

Let me recommend "Surely You're Joking Mr. Feynman" It is light reading and very funny in places.

A follow-on is "What Do You Care What Other People Think?"

E**(Pi*i) +1 = 0


I have both of those books. Pure gold!

Carl