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  1. CPW

    Isotope decay via alpha and beta particle emissions

    What does your textbook say happens during alpha decay? (How does the atomic number Z and the mass number A change?) What does your textbook say happens during beta minus decay? (How does the atomic number Z and the mass number A change?)
  2. CPW

    Electric field due to a flat hollow disk

    I agree. Nice work. But with y axis up in your figure, shouldn't you include a minus sign in your vector answer?
  3. CPW

    Electric field due to a flat hollow disk

    It appears to me you are on the right track, but is the problem asking for the E field at the center of the semicircles? Can you explain why sinθ and not cosθ?
  4. CPW

    Three charges attached to the vertices of a triangle

    You will need to use math. Solving a similar example problem, with the algebra and trig being performed on symbols (saving the numerical substitution for the last step), may provide you with the insight you need for this homework problem. See this solution, and don't just read it. Instead...
  5. CPW

    B Pre 2019 definitions for an Ampere, how is this useful in practice?

    Good question. Consider the size of one Newton of force: about equivalent of holding up an apple in your hand in Earth's gravitational field. A human-sized force. Is your concern about the SI definition of the unit for electrical current that the forces involved are so much smaller? Sensitive...
  6. CPW

    Curvilinear... isn't that a strange word?

    Hi PF. I'm over ten years out from graduate school in physics, and I still enjoy re-reading my textbooks. I came across the word curvilinear, and thought how strange a word it is; a juxtaposition of curved and linear, which are at times understood to be opposites. The textbook was describing...
  7. CPW

    Stargazing M - M as the distance modulus, and a question about the distance ladder

    Hi phyzguy. Yes. The gap in my knowlege about this topic is no longer there. I think I just needed to settle on the fact that the period - luminosity relationship of cephiad variable stars was a discovery. A revealing of a fact of nature, discovered by Henrietta Leavitt. The comments and...
  8. CPW

    Stargazing M - M as the distance modulus, and a question about the distance ladder

    I'm attempting to understand fully the distance ladder we use in astronomy to determine the distance to stars that are too far away for parallax to work. I understand we calibrate to a standard candle data of period vs luminosity for the cepheid variable stars in a group. Then from knowing the...
  9. CPW

    Question of Rotational motion

    In determining the reaction force on the cylinder by the wall, consider that there is no translational acceleration of the center of mass of the cylinder.
  10. CPW

    I A Puzzle Involving the Moon's Orbital Motion

    This delightful puzzle you posted reminds me of a question I like to ask my work colleagues (non physicists): "So, the sidereal period of Earth's rotation is not 24 hours. It is 23 hours and 56 mins. Shouldn't that fact mess up our time keeping within a few days?" I'm always impressed with...
  11. CPW

    Galileo's tower of Pisa experiment

    I have two textbooks from when I took this course (over a decade ago): Fowles & Cassiday and also Thornton & Marion. In the first book, the drift to the East for free fall (example calculation for experiment on Earth's surface at latitude 45 deg), is explained in terms of the Coriolis force and...
  12. CPW

    B Can a pool ball come off a cushion faster than it hits it?

    There are other KE of rotation + KE of translation examples to elucidate the above explanations to your question. Consider the rolling down an incline of a sphere vs hoop vs solid disc. Thinking of that example helps me understand how a billiard ball's spin prior to collision with the cushioned...
  13. CPW

    B Radon testing my first basement (already has a mitigation system)

    Just received the long-term test results: 3.8 pCi/L, just below the EPA limit of 4 pCi/L. The test kit was in the basement for 105 days, and the report states the uncertainty in the result is +/- 15%. My wife and I intend to let our kids play in this unfinished basement some. I see that there...
  14. CPW

    What is the total amount of paving in the US?

    While commuting I'm listening to The Great Courses "How the Earth Works" lecture series, and in one lecture the professor stated that the amount of paving (asphalt on the ground, buildings, concrete, etc.) in the United States is now greater than the area of the state of Ohio. The lectures were...
  15. CPW

    Misc. Getting used to new house, but what's best for noise elimination?

    The noise level is getting slightly lower in the main living area as my wife and I put your recommendations into our furniture and decorations. Thank you again for all your comments and advice.
  16. CPW

    Misc. Getting used to new house, but what's best for noise elimination?

    We have a large area rug on the floor. Perhaps I should put another one under the kitchen table in this great room. But with the family, the hardwood floor is easier to clean up after meals. Thank you for your advice.
  17. CPW

    Misc. Getting used to new house, but what's best for noise elimination?

    So, my wife and I really like our new house, but after living in it for two months we desire to find a smart way to deaden the noise. You see, our previous house was smaller, had carpet mostly, and did not reflect the noise inside near as much as this new house. Our new house is larger, has...
  18. CPW

    Possible to calculate the strength of a nuclear explosion from a photo?

    I just reviewed the link to the GI Taylor calculation (link above from phyzguy), and I understand the dimensional analysis. I appreciate the approximations made, and so I think that the answer is in the correct order of magnitude. In fact, I find this calculation very interesting and a useful...
  19. CPW

    Possible to calculate the strength of a nuclear explosion from a photo?

    Details of this calculation from the photo?
  20. CPW

    B Radon testing my first basement (already has a mitigation system)

    In case anyone on this thread is interested, I received the results of the short-term radon test: 3.0 pCi/L. I'm relieved that it is less than 4.0 since my wife and I went forward with this home purchase without getting a radon test first. As stated above, the home already has a radon mitigation...
  21. CPW

    Finding Equivalent Resistance, Current, and Voltage across a resistor

    Hi again. Ok. The loop rule I mentioned is what you have obviously been taught (Kirchhoff's Voltage law). I see your equation: -160 + 40i1 + 8i1 = 0. But you made an easy mistake in that equation. The current throught the 8 ohm resistor is not i1, but rather it is iS = 5 A (the same as the...
  22. CPW

    How did Euler come up with the value of e?

    The group of us on this thread should mark our calendars to commemorate this conversation on February 72, 2020. The nerdier holiday than March 14th.
  23. CPW

    Finding Equivalent Resistance, Current, and Voltage across a resistor

    Hi Rugerts. Answer A is correct. But answers for B and C are both incorrect. (Answer for B is asking for current I1) I1 + I2 = Is where I1 and I2 are both unknown, and Is is the 5 amps you correctly calculated. The method I learned was then to write an equation for the voltage rise and drops...
  24. CPW

    I What are the potential effects on electricity due to Earth's magnetic field reversal?

    For the next magnetic field reversal on Earth, do we have an esimate of how weak the main field strength will be during the flip? I'm trying to think what society could do to mitigate the effect of more ground level radiation (ionizing radiation) at the lower latitudes. Are there lessons we...
  25. CPW

    B Radon testing my first basement (already has a mitigation system)

    Hi Russ. We are the second owners of this nice house, built in 2016. The builder installed the radon mitigation system, and it is working (at least the blue U-shaped manometer shows the fan is working). I'll find out the radon levels with both a short-term test and a long-term test from...
  26. CPW

    How did Euler come up with the value of e?

    This is an interesting question, and a short book has been written on the history: Author: Eli Maor Book: e - The Story of a Number I enjoyed reading it when the same question you posted was on my mind. https://www.amazon.com/dp/0691168482/?tag=pfamazon01-20&tag=pfamazon01-20
  27. CPW

    B Radon testing my first basement (already has a mitigation system)

    Thank you Russ. One more question comes to mind: In a few years, when we finish the basement, there will be another HVAC system for the basement level, which will circulate the air. Will that reduce radon levels too?
  28. CPW

    B Radon testing my first basement (already has a mitigation system)

    Hi PF: The house my wife and I purchased recently is our first one with a basement and it already has a radon mitigation system installed. Unfinished basement. I've sent my short-term test to the lab and I have a long-term test that I intend to start this week. Do any PF members have any...
  29. CPW

    I Details in calculations from 19th century astronomy

    Thank you for explaining the methodology of the calculation. That makes this famous bit of science history more understandable to me.
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