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About druS

  • Rank
  • Birthday 05/19/1962

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  • Location
    Sydney Australia
  • Interests
    Science - Inspired by Sean Carrol to attempt to learn the math behind Quantum, and picking up a life long love of biology at the same time.

    Rugby (Union), 4WD
  • College Major/Degree
    Bachelor Building
  • Favorite Area of Science
  • Biography
    From Queensland originally, lived in the UK for 10 years. Represented Britain in the 2007 Skydiving World Cup ("also rans" but fun).
  • Occupation
    Technical Services (Development and Construction)

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  1. Thanks Strange, yes I meant ST not SR. I had understood that in principal the energies required to test ST are impracticable. IS that just too simple an approach in terms of dumbing down the theory for the populace? Otherwise the difference between untestable and unfalsifiable seem hazy. It starts feeling like pure math (presuming the axioms stack up) rather than science at that point.
  2. Question from a novice to the brains trust here. It has been said (sorry I cant quote the source but variously and probably pop science) not simply that SR hasn't been proven, but that it is unfalsefiable. That is not a subtle difference. I have also seen Sean Carroll state it doesn't matter, that it is unfalsefiable for now but someone will resolve it at some stage. But that does seem to contradict one of the basic tenets of science - leading the topic into either math or conjecture.
  3. RIP Gell-Mann. We lose a great scientist here.
  4. As someone very very early on this journey and doing it very late - I'd appreciate if you could expand on this. My personal experience is that my curiosities are too broad and defining a study course through my interests, and doing this somewhat efficiently through how quickly I can gain qualifications, well these things are diametrically opposed. I am fascinated by the concept of Masters v PhD. I get the different levels of academic interest/ability but there are always going to be details that sit around this. A M Science should not EVER be sneezed at.
  5. I love this place. Completely unexpected but occasionally something goes "Hell, what happened there? It's something right on the tip of my ability to understand." An issue then to drive study. swansont, thanks. But to be fair, rock on Itoero. If you weren't making noise mate, I'd be missing these opportunities. Love this community, thanks all.
  6. I'd approach this more from engineering, or perhaps physics. The average set of lungs holds approx 6l and when you fully breathe out there is a residual approx 1.5l So if you exhale a contaminant mixing inside your lungs there is only 1/4 of it left - at the same concentration so you are still consuming it the same way. Inhale non contaminated air and it has been diluted to 1/4. Note though that the whole time your lungs are consuming whatever it is.
  7. druS

    Rotational motion

    Yes appreciate it.
  8. druS

    Rotational motion

    Yep. Seems my biggest issue was the free body diagram to the falling book. Weird. Not a difficult thing, surely. And yes, puzzling out these things is rewarding.
  9. druS

    Rotational motion

    Thanks again. Yes this final step didnt stress me too much. accel = alpha x R; T = F x R Sigma T = I x Alpha Which ultimately gave me 0.16 kg.m/s which is text consistent. Are there easy and simple introductions to LaTex? Probably dont have time to test it mid trimester but it is goinng to have to happen sooner or later. Thank Studiot.
  10. druS

    Rotational motion

    Cheers guys. Waking up in the middle of the night with a brain spark started by this conversation. Yes I've been visiting and cogitating. Studiot, I suspect our formula are equivalent though I like the accuracy in the way you express things. I'll stick with the formula sheet in our sample exam papers though. Swansont I think I was jumping to the next step in my head, looking for the moment of inertia. not focusing on one issue at a time had me applying Newtons 3rd law incorrectly. Acceleration works to 3.75m.s-2 (matching Studiot's more accurate expression). And going down is negative. For the 3kg hanging book I get a tension force above FT = m.a = 3.0kg x 3.75m/s2 and weight acting down W = m.a = 3.0 x -9.81 AND what I was missing a resulting force FR = m.a = 3kg . 3.75m/s2 [Sum of] Forces = 0 FR = FT + W (the bit I did not have right!) 3 x (-3.75) = FT + 3.00 x (-9.81) providing FT = 18.18 N Then I was wracking my brain with the 2kg book on the (frictionless) table. The only difference is that there is no relevant weight force (normal force and weight cancel to zero in the y direction). (What I had been doing incorrectly for the 3kg book) In the x direction the resultant force simple equals the tension force and we get 7.5N. Which fortunately matches the text answers. OK next step? I'm presuming that the torque applied by these tension forces will not equate to the actual torque observed and the difference will be related to the moment of inertia of the pulley. (but just for now it is 3:20 in the morning and I'm going back to sleep a happy student).
  11. druS

    Rotational motion

    So the second law is F = m.a And I wish I could start there. Let's start with the lower book. So (oh good, the cat decided to join this conversation) x = x o + vo.t + 1/2 at2 I am focused on the lower body, get an acceleration of roughly 5.6m/s2. OK How do I translate this to the tensions.
  12. OK I'll give this forum a go. It is not actually homework, but study that is related and extra. A 2.00kg textbook rests on a frictionless, horizontal surface. A cord attached to the book passes over a pulley whose diameter is 0.150m (my note R = 0.075), to a hanging book with a mass 3.00kg. The system is released from rest and the books are observed to move 1.20m in 0.800s. a) What is the tension in each part of the cord? b) What is the moment of inertia of the pulley about it's rotational axis. This is an end of chapter question Q 10.13 in the global edition of University Physics with modern physics by Young and Freedman. I (think I) can work the basic kinematics on distance and time and capture an acceleration. I haven't managed turning that into the cord tensions. I think I can find an angular acceleration in the pulley which means i should be able to find moment of inertia. But it has not at all worked. Who wants to guide a newb through what must be a pretty basic question?
  13. When I think of "living fossil" my first thought are cycads. Now the cycads alive today are obviously different from the cycads known from the fossil record, BUT there are more species known from fossil than are alive today. Predate flowering plants on earth. Since reading Tim Low's latest ("Where Song Began - Australia's birds and how they changed the world"), I also think of the Australian lyre bird. Not really a living fossil, but certainly a direct descendant of possibly the first song bird. In these discussions we need to reconsider the term "primative" - where it is thought to mean poor and rudimentary. In many ways these species have extraordinary strength in survival.
  14. I think this one is easier to cogitate for a beginner by NOT thinking of particles colliding. Try waves instead.
  15. Studio, apologies but I'm busy in study at the moment. Thanks for your insight. As usual, will come back to this as time permits.