Recent content by Dr Dr news

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    B Confused about the ideal gas law

    You might try this. p(1)V(1) = n(1)RT(1) and p(2)V(2) = n(2)RT(2) and V(1) = V(2) and n(1) = n(2). Divide eqn, 2 by eqn. 1 and solve for T(2).
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    B Thermionic emission and current density

    What you are describing here is close to what we called thermionic energy conversion in the 1960's. The object was to place two electrodes in close proximity, heat one of them until thermionic electron emission occurs. The electrons with sufficient kinetic energy could cross the gap and be...
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    I Direction of the magnetic field of the Earth

    This just in from the morning newspaper. The Earth's magnetic field intensity is weakening and magnetic North is moving towards Siberia at 34 miles/year. All of which makes a case for relying on GPS rather than compasses.
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    B How is momentum conserved if you lose kinetic energy?

    One of my favorite demonstrations in Mechanics is to take two carts of identical mass on a track with velcro affixed to their front bumpers and give them equal and opposite velocities. The system of two carts thus have zero momentum before colliding and stopping in the middle of the track. The...
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    Chernobyl and steam explosions

    Consider a pressure cooker. As heat is added to the constant volume of the cooker, the liquid water is converted to vapor increasing the pressure which increases the boiling temperature which further increases the pressure until the pressure relief valve is opened, releasing some vapor and...
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    Am I looking at the right Physics textbook?

    On a scale of 1 to 10, I would give Young and Freedman a 7. This text was formerly Sears and Zemansky, a standard text, and was inherited by Young. The first several editions published under his name were replete with errors. Maybe it has been cleaned up by now. One can only hope. Good luck.
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    I How does the pressure drop as a fluid flows through a pipe

    The velocity profile across the pipe transitions from uniform at the entrance to about parabolic further downstream. To determine the total pressure, you need to integrate across the velocity profile.
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    DIY vacuum chamber advice

    If you are going to use a metal base plate, you can drill and tap your base plate for the pipe thread of a spark plug and use glyptal to seal the threads. Spark plugs make great high voltage feedthroughs. We made some simple vacuum systems with thick-walled, one foot ID glass cylinders and...
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    DIY vacuum chamber advice

    I did a lot of thermionic emission experiments in high vacuum during the 60's and even built a glass vacuum system tied to a LN cold trap, diffusion pump, and fore pump and an oven to bake and outgas the glass components. Temperatures were measured with an optical pyrometer and W-Re TC's...
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    I Error propagation and standard deviation

    You might check Kline and McClintock's 1953 paper on uncertainty analysis. It is a standard in the field.
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    Am I looking at the right Physics textbook?

    All the above comments are good advice. I have a four foot stack of introductory Physics texts we have used over the last 30 years. My favorite is Serway which is used by many universities. The introductory calculus-based courses are usually a total of nine credit hours spread over two or...
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    Tangential Acceleration/Tension

    srekai: Your solution is correct. v^2 / rg is in fact dimensionless.
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    Shooting distance

    Your methodology looks OK but 1) the moment of inertia of a rod about one end is mL^2 / 3 and the moment of inertia of the rock is ML^2; 2) the potential energy of the lever and rock in the vertical position is mgL/2 + MgL. Make those changes and recalculate the distance and I'll let you know...
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    Why don't voltages add up numerically in an LCR AC circuit?

    The best way to see this is to connect an oscilloscope across each element. The differences in phase will be apparent.