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  1. BvU

    Length of a moment of eternity

    The Grimm brothers wrote fairy tales. Grim ones :rolleyes: But they don't say it's the same bird. Just "a little bird" If the mountain's circumference is 5 km, it doesn't take one hour to climb it -- unless it's a sky scraper. And diamond doesn't wear from a bird's beak. And the first second...
  2. BvU

    Vector Mechanics Question -- Double Gear Rolling on a Rack

    You forgot to define ##\theta## (Solution forgot it too !) Ask youriself: how far does ##A## go to the right for one revolution (##\theta = 2\pi##) ? For half a revoluton ? For a given ##\theta ## ?
  3. BvU

    Optical Measurements of the Sun's radiance and ray tracing

    That's not how it works. Rays from the sun come in almost parallel.
  4. BvU

    Learning physics from scratch

    That helps a bit. My compliments for this curiosity ! (I was like that long ago when there were only books). And have you outgrown the sites you get when googling physics for kids ? If so, google college physics books
  5. BvU

    Learning physics from scratch

    Hello @Neeleshatom , :welcome: ! Does scratch mean you have to learn reading and writing ? No. What does it mean ? Makes a difference. Here at PF we value initiative: Go find a book at the level that suits you and start doing the exercises. We can't recommend anything if you don't tell us more...
  6. BvU

    LaTeX For an informal presentation, would you use LaTeX to type this out?

    Don't know if my comments post was deleted, or that I simply messed up and didn't post. Your specimen sure looks different from the last time I saw it. I had: kudos for the ##\TeX##ing ! Was it indeed a few hours, or much more ? pity you don't post the ##\LaTeX## source, this makes referring...
  7. BvU

    Optical Measurements of the Sun's radiance and ray tracing

    No. You even calculated the angle ! And it should be at practically infinity, not at a few decimeter
  8. BvU

    [Equation Validity] - Current Characterization (AC) in Sockets

    The way it was written, OP postulated one single frequency per load. I agree a Fourier series per load makes more sense
  9. BvU

    [Equation Validity] - Current Characterization (AC) in Sockets

    When I look, I see Only a single ##p##, so all loads show the same phase lag ? multiple frequencies, which is strange: the mains only has one frequency So: no, I don't think you are on the right path. Advice: read up on AC circuit analysis.
  10. BvU

    I Why is the speed of light absolute?

    Ours is not to reason why. It is. And that it is has been confirmed by experiment. By the way, what would constitute a satisfactory answer to your question ? And why is the ratio of circumferernce of a circle to diameter equal to ##\pi## exactly ? See also
  11. BvU

    A EM field in the Harmonic Regime -- I'm not understanding this step in the Derivation

    You can even just cut and paste. And if the useful part is only a fraction of the whole picture, PLEASE use snippet to copy only that part !
  12. BvU

    (SOLVED) Newton's 1st law

    You forgot the problem statement. What is the exercise ?
  13. BvU

    Engineering How did they find this angle?

    Post the complete problem statement !
  14. BvU

    Engineering How did they find this angle?

    That's a statement of your problem, not of the homework problem. Provide a complete problem statement given: knowns: unknowns: This way, so am I ! ##C## doesn't exist ?
  15. BvU

    Mass and vibration frequency

    I don't understand the question :confused:
  16. BvU

    Mass and vibration frequency

    Correct. Inertia wins.
  17. BvU

    Mass and vibration frequency

    Hello Deepesh, :welcome: ! Vibrations occur when there is an equilibrium situation and some restoring force that works towards this equilibrium. The simplest way to describe this in physics (mathematics) is $$m\ddot x + kx = 0$$with as solutions ##x = A\sin(\omega t + \phi)##. Substitution...
  18. BvU

    Closed vs Open Electrical Circuits

    Hello W5, :welcome: ! I would venture things are even more complicated: open is current = 0 short-circuited is voltage = 0 closed circuit is anything in between This is DC with perfect conductors and perfect insulation. Would be nice if everything was black xor white but we have gray as...
  19. BvU

    I What techniques and equipment are used to measure the length of one meter (without circular reasoning)?

    You meant it isn't possible ? All you have to do is vary the position of the reflecting mirror -- with great precision, because you are searching for a few nm (or less) intercept
  20. BvU

    Pressures in a U Tube along a line - different liquids

    If the bottom is rigid, fixed, attached, welded to the sides, the force needed is the force to carry the container including the liquid. The container bottom exerts the offsetting force for the water column pressure. If the bottom is a piston, the force needed is the force to keep the piston in...
  21. BvU

    A critically damped simple harmonic oscillator - Find Friction

    Hello @muskaanhamad , :welcome: ! I can't agree with that: you calculate an average velocity so you find an average force. Unfortunately, the wording of the problem statement is unclear: 'the force' ? I did a simulation of your scenario: and as you can see the force starts at -7.5 N (namely...
  22. BvU

    Why is 2Δx = Δy in this problem?

    Very nice picture !
  23. BvU

    I What techniques and equipment are used to measure the length of one meter (without circular reasoning)?

    Consult https://en.wikipedia.org/wiki/International_System_of_Units for the definitions For physical constants measurements and fitting procedure there is https://www.nist.gov/pml/fundamental-physical-constants (full fitting article here) Google measuring the speed of light -- get this as...
  24. BvU

    Flux due to a charge located at the corner of a cube

    The flux through a cube of 8 times the size where the charge is at the center would be answer E. Your cube is 1/8 of that (with the other 7 identical). Hence answer B. I don't think the exercise composer want you to worry like @Abhishek11235 in his/her last post: the faces with the charge in...
  25. BvU

    Why is 2Δx = Δy in this problem?

    Hello johni, :welcome: ! Yes. What I do is draw the setup with a visible ##\Delta x## (e.g. half-way to the wall) and then I check which pieces of rope have changed length. You also have to worry about signs. Which way is positive in x and y ? [edit] slower than @PeroK but it's good to see...
  26. BvU

    Pressures in a U Tube along a line - different liquids

    Absolutely not ! Compare sheets 9 and 10 in the link. In the first, holding up the piston requires 150 kgf, both left and right. In the second, the bottom of the container is holding up the liquid column, and whoever holds up the whole thing carries the total mass, which is small on the left...
  27. BvU

    How do atoms emit different photon energies?

    Nevertheless: tell us what you know and did to come to an answer...
  28. BvU

    How do atoms emit different photon energies?

    well, what about the lengths of the arrows ? Are they all the same ? What do they represent ? and what does img_3305 have to do with this at all ?
  29. BvU

    How do atoms emit different photon energies?

    This homework ? If so, then post in introductory physics HW forum and tell us what you know and did to come to an answer...
  30. BvU

    Question about linear transformations

    Hi, I don't understand what you are doing. Could you clarify your symbols ? e.g if you write $$T(1,1)=A*(1,1) =(2,0)$$ it looks to me as if you think ##T = A##. I also get another result:$$ A \begin{pmatrix} 1\\ 1\\ \end {pmatrix} = \begin{pmatrix} \phantom - 1 & 1 \\ -1 & 1 \\...
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