Recent content by checksix

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    Undergrad Learn Physics with Eigenchris: Relativity & Tensors

    I found the videos extremely helpful. I'm just a novice and struggled with MTW, etc. on my own without much success. I appreciated the way he (eigenchris) used simplified notation in the beginning then added more details as needed, rather than bombarding the reader with everything all at once. I...
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    Undergrad Gradient as vector vs differential one-form

    pervect, as usual you give such a simple and readable explanation of a concept. Thanks from a quiet lurker here.
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    Undergrad Equivalence Principle & Geometry: Ben Crowell's General Relativity

    Got it. Thanks!
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    Undergrad Equivalence Principle & Geometry: Ben Crowell's General Relativity

    In the first sentence of Chapter 2 in Ben Crowell's "General Relativity" he states: "The geometrical treatment of space, time, and gravity only requires as its basis the equivalence of inertial and gravitational mass". This is stated as if it's an obvious fact, but I don't understand why. Why...
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    Undergrad Using Black Holes to Time Travel Into the Future

    Slightly off topic for a physics forum, but an interesting sf novel written back in 1970 by Poul Anderson explored the issues of forward time travel using relativistic speeds: https://en.wikipedia.org/wiki/Tau_Zero
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    High School Why does light move at the speed it does

    Perhaps the answer that the OP was looking for is that the reason light travels at the speed it does, is because the universe is apparently constructed with a speed limit. Light, being massless, can travel faster than anything else, but it cannot travel faster than the speed limit. Physicists...
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    Graduate Gravitational flux and divergence theorem

    Thanks, that helped. So I guess, in a sense, it is the field itself that is "flowing". Or maybe not. Perhaps it's best not to press too hard on the fluid analogy and just trust the formalism.
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    Graduate Gravitational flux and divergence theorem

    Hi. I've been reading PF for quite a while and have decided to ask my first question. Please be gentle. (I'm a retired computer programmer, not a student)... I've been learning Gauss' divergence theorem and I understand what "flux density" is when considering things like fluid transport or...
    • checksix
    • Thread
    • Divergence Divergence theorem Flux Gravitational Theorem
    • Replies: 2
    • Forum: Electromagnetism
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    High School Research F1 Physics: Basics & Beyond

    The downforces are amazing. These cars could literally run on the ceiling if the track was built upside down.
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    High School What Makes a Good Starter Telescope for a College Astronomy Student?

    A star chart and small binoculars are a great way to start out. Learn the names of the bright stars and constellations. Find the planets. You'll be amazed at the number of (non-stellar) objects you can see without a telescope.
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    Stargazing Need Help - Learning to use a telescope

    Perhaps the mirror is out of alignment and is not pointing down the centerline of the tube?
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    Identifying a Bright Celestial Object in FL, USA - Eraniamayomii

    Print your own star chart here: http://www.telescope.com/control/category/~category_id=lc-month-starchart/~pcategory=lc_in_the_sky
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    Undergrad Is the 'Equal Transit' Theory Really True? A Closer Look at Airplane Flight

    An interesting book on this subject is "Stop Abusing Bernoulli! - How Airplanes Really Fly" https://www.amazon.com/dp/0964680629/?tag=pfamazon01-20
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    Graduate How Do Covariant and Contravariant Vectors Differ in Tensor Calculus?

    Bing. The light bulb finally goes on. I've struggled to understand this for quite some time, and was starting to get close, but your post makes it so clear now. Thanks Ben!
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    Calculating Reading Score with a C Program

    Your problem is the semicolon on this line: while(fgets(text,sizeof(text), input)); It's acting as a null statement. Just remove the semicolon.