Recent content by Janus

  1. Janus

    I Relativity of simultaneity doubt

    If you are in a spaceship flying towards the Moon, measuring how long it takes for a light signal to travel from Moon to Earth, you measure the signal as traveling at c relative to yourself, and the Earth as moving at kc away from the point of emission. So for example, if we assume the Moon is...
  2. Janus

    I Falling in an O'Neill Cylinder

    While standing on the inside of a rotating cylinder, you are accelerating. Acceleration is a change in velocity, and velocity includes both speed and direction. Since the cylinder fall is forcing you to travel in a circle, and this causes you to constantly change direction, you are...
  3. Janus

    B Speed of light versus wavelength

    Think of it this way: Light is like a train and the wave length is the length of each individual car. If the train travels at 10 m/s and each car is 10 m long, then the frequency at which cars pass is 1 car/sec. If the cars are 5 m long, the same train speed produces a frequency of 2 cars/sec...
  4. Janus

    B How long it takes the Earth to fall halfway to the Sun--ellipse method

    Towards the end of this article is an equation which allows you to calculate this. https://en.wikipedia.org/wiki/Equations_for_a_falling_body
  5. Janus

    I Relativity of simultaneity doubt

    From the ground observer view, the train is moving away from strike A and towards strike B. By the time he sees the light from both strikes, the train observer has moved to a point closer to strike B and further from strike A, in other words, the light from strike B will have already passed the...
  6. Janus

    Random Photos

    Throughout Portland there are older streets which still have horse rings on the curb. As a part of something called "The Horse Project", people will attach toy horses to these and take a picture. We ran across this one on our neighborhood walk recently.
  7. Janus

    Home Repair & Maintenance Advice for Newbie?

    That's how I started. Dad would have me hold the board as he sawed it, have me fetch tools, etc. Over the years it evolved into our adding an addition onto our house and moving the Kitchen. Along the way I learned everything from pouring a foundation to wiring and plumbing.
  8. Janus

    How hot is it? - 2021

    We had another bout of flirting with 100 F temps just recently with nighttime temps only dropping to the 70s. Then last Friday, I woke up to a temp of 49 and it didn't even make it to 70 that day.
  9. Janus

    Space and time -- Is the term "light year" really correct?

    A light year is a unit of distance It is simply the distance one would travel in 365.25 days (a Julian year) if you were moving at c.
  10. Janus

    The difference a new computer makes for 3D rendering

    Your friends computer would have to have the same 3d software as you have ( for instance, blender). Then once you are done, you can just export the blender file for your scene( and any other file; image etc) to his computer t do the render. You will have make sure the render settings are...
  11. Janus

    I Absolute and relative motion/rest

    You have to apply a force in order to go from moving with respect to the Earth to at rest with respect to it also. Now you might argue that you needed to use your engine to get moving relative to the Earth, and only had to apply brakes to come to rest, But you can also say that all the brakes...
  12. Janus

    Artificial air on Mars

    There are nitrogen fixing plants that, with the help of bacteria, can use nitrogen directly from the air. Farmer use these in rotation with other crops to replenish nitrogen in the soil. https://en.wikipedia.org/wiki/Category:Nitrogen-fixing_crops
  13. Janus

    I Rotation curve with neutral hydrogen and dark matter

    The solar system as a whole has a much higher density than the galactic disk in terms of baryonic matter. So even though the density of DM is roughly the same, the ratio of baryonic to dark matter in the solar system is extremely high compared to the disk as whole. Thus in the solar system...
  14. Janus

    How hot is it? - 2021

    Unfortunately, I think that was the gist of it. That this is typically an extremely rare event that it likely to become less rare.
  15. Janus

    How hot is it? - 2021

    Luckily, we didn't have to go anywhere, and were able to stay inside with the AC on*. 115 is a bit warm for my blood. It's supposed to only reach 95 tomorrow and cool off to 69 tonight ( last night it only got down to 82). I heard somewhere that this is something like a once in a thousand...
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