Charles D

My girlfriend has a single white pustule just inside her vaginal lips--about 2mm across. It has recently turned black--full of blood, I suspect. I mentioned it to her once and asked her another time if she knew what it was. She said she didn't know.

I haven't pressed it, but now she wants to have unprotected sex--saying she's on the pill and has a condition wherein her eggs are not viable anyway.

I'm not concerned about the pregnancy risk, but am concerned about the STD risk. In her history, she has insisted on protection, but I know she's been with a riskier crowd in the past.

So I'm looking for ideas as to whether this is in need of testing or just a benign quirk or her anatomy. Herpes doesn't change color like this. I'm trying to be diplomatic with her, and don't want to "ruin the mood," so I'm asking for medical advice here instead of forcing her into testing. Smart, right? (So feel free to scold me for not pushing the point harder with her--sorry, bad choice of words.)

or maybe it was a bowling ball. Anyway, they fire an object (a barrel or ball, as I recall) out the back of a van driving 60mph. The firing mechanism had been calibrated to fire the object at 60mph. So when fire from a 60mph van, the object gently lands on the ground right below where it was fired from the van. Have been through the episode list on Wikipedia. Have used a search engine, but no luck... partly because the first several pages are the cannonball incident in which they hit a couple houses and minivan... not the same experiment. If you can locate the episode number for me or a video of it, that'd be great. Thanks in advance.

Charles

In Illustrator, blowing up a PDF on screen reveals clear detail. But how to save this detail in another format so I can forward the image to an online poster-making company? I've tried several permutations of saving in different formats in different sequences. If you have anything for me to try, I'm open to suggestions. I assume I'm missing something simple. It's such a basic, desirable operation that it can't be that hard, right?

Thanks.

Hi,

I have vectorized a line drawing (PDF), so that it looks nice and sharp when blown up on the computer screen. Now I want to save it with that kind of detail, so I can send it to an online service to make a poster. But I need to send them a high-res image, say, at least half a Mb. I don't see how to do this in Illustrator. When I save for the Web, e.g., as a JPG, the detail is lost. I've done several permutations of the order in which I save it, including blowing it up as a PDF 400%, saving it as a PDF, and then reopening it to save it for the Web as a JPG. Even this doesn't preserve the detail upon saving.

Thanks for any hints.

When the hydrogen has been burned up and heavier elements are being created, why would the Sun expand? It seems to me that as less-efficient forms of fusion dominate, there's less energy output to push out the Sun's mass, making it contract. Even if the core becomes denser, the mass still is concentrated at the center and so the gravitational pull on outer layers should not change.

Thanks!

Looking for the blackbody temp of these things. Funny, but I couldn't find any info on the Internet about this. Seems like it would be important for anyone wanting to make such items so that the metal/glass withstands the temperature.

Thanks.

Using a 9V battery, I'm having trouble getting light bulbs to light and an electromagnet to work. I was told that I need to consider amps. E.g., a car battery has only 12V but can electrolyte you, while 9 D-batteries can't do anything like that. I'm trying to understand this. So while two batteries can have the same voltage, the amperage is different. But I don't understand that. If the internal resistance is negligible, then the resistor connecting to the battery would determine current, I, by the definition of resistance: R=V/I. So how can current vary when V and R are the same?

Thanks!

physics

A child runs tangentially to a merry-go-round's rim. The kinetic energy of the system then goes down, even if the child was running faster than the rim. So even if the rim picks up speed, the system's KE goes down. That's why you have to use conservation of angular momentum instead of conservation of energy to solve for, say, the final angular velocity.

But where did the "lost" energy go? Of course, it ends up as stored elastic energy in the bending of the axis of the merry-go-round. It's the energy required to divert the child's inertia into circular motion. Now, obviously this potential energy can be found by taking the difference of initial KE and final KE. But is there no other way of evaluating the energy of centripetal motion? Seems like there should be a simple formula for the energy resulting from circular motion.

Or is it like the car collision problem, or the ballistic pendulum problem, where there's no formula for the energy "lost" but it can always be calculated?

Thanks in advance.

If you squeeze the bulb of an atomizer, you increase the pressure of the air within. Meanwhile, the pressure in the perfume's container is the same as the outside pressure's. So can't the pressure of the stream between the bulb and the opening at the other end be greater than that in the perfume container, so that the perfume doesn't get sucked up into the high-velocity stream? Yet the explanations I see seem to suggest that the pressure in the bulb is the same as in the perfume container. But for that to happen, the air flow direction has to be from the bulb into the perfume container, not from the perfume container into the high-velocity stream.

Thanks for any help in setting me straight.

Charles

If wavelength drops due to relative velocity between observer and emitting galaxy, where did the energy go? The way I view it is that if you throw a tennis ball against a wall from a receding car, then naturally, it won't hit the wall as hard. Same thing with the light. The photon's momentum must go down because the object "throwing" the photon is receding. Am I on the right track?

Thanks!

Diastolic pressure is when the heart is relaxed. But how could that be found by listening for a pulse with a stethoscope? I would have thought that the weaker of two pulses of the heartbeat is what doctors listen for, and therefore the diastolic pressure operationally is the pressure of the second, weaker beat of the heart. I'm having trouble reconciling the definition with the diagnostic procedure. Thanks for any help in reconciling this for me.

Charles

I heard that the shallowness of the Great Lakes (due to their being created by glaciers) leads to more violent storms. One idea I had for why this is is has to do with the reason tsunamis don't have much effect until they reach shallow waters and really start piling up. In other words, shallowness can funnel the potential energy of wave heights into much greater wave heights, if the configuration is right. Another idea I had was that it's a seasonal effect. The warmer land under the lakes and colder air above (due to water's high specific heat capacity) leads to thermal inversions. (I have a hard time imagining the sea floor's heat drives storms though.) Any other ideas?

Thanks in advance.

If you tie a ping pong ball to a hair dryer, you can point the hair dryer horizontally and the high velocity above the ball will give the ball lift, pulling the connecting string taut. Now, I know there are many misconceptions about the Bernoulli equation, but I clearly haven't mastered them. The way I view this demo is that the fan in the hair dryer causes higher pressure, which creates the higher velocity. So the streamline for a particle of air goes in through the back of the hair dryer and out the front at a higher velocity, because of energy imparted by the motor in the dryer. So this isn't really Bernoulli's equation at work. Bernoulli's equation has energy conserved along a streamline in which no additional energy is transferred into the fluid along the way--aside from a change in gravitational potential energy. So the idea that the velocity went up while the pressure went down doesn't apply, in my mind. The velocity went up because a pressure gradient was imparted by the fan. So the high-velocity air has pressure equal to the ambient pressure, or more. So lift shouldn't occur. Yet it does. So I'm pretty confused.

Thanks in advance for any help.

Charles

Why does a proton-antiproton collision have more energy than a proton-proton collision? I simple-mindedly presume it's from electrostatic attraction just before they collide but that doesn't seem to be where the Wikipedia article on the antiproton seems to be going with it.

Thanks for any insight.

Charles

A recent teacher cert multiple-choice test asked which is best for increasing the velocity of an electron as i hits the phosphor on a screen: the vertical diverter's charge, the horizontal diverter, the cathode temp or the anode voltage. Of course, the answer is the last one. But what about temp? I figure that's a bad approach because it's easier to double voltage than to double temperature. To double the temp in the cathode would require much more than a doubling of the current in the cathode. Or do I have that wrong? I'm just trying to reason this based on equations, but I'm not coming up with what the relevant equations are to decide if this is just a sorta inefficient approach or a REALLY inefficient approach.

Thanks for any insight.

Charles

I was trying to help a student to calculate the cross section for a particular element that was stopping 9,999 out of 10,000 thermal neutrons if the wall was 0.1mm thick. My strategy was to find the number of atoms in a volume with area 1mm x 1mm (and of course 0.1mm thick) and divide this into the area.

But the trouble with this reasoning of course is that it assumes the stopping effect of the neutrons is linear. In other words, there's no shadowing going on. If you double the plate's thickness to 0.2mm, then, um, 19,998 out of 10,000 thermal neutrons would be stopped. Makes no sense.

So how could I incorporate the shadowing into the calculation? The text barely mentions cross sections, so I assume it's something simple enough to be taught in first-year physics, but I'm just not getting it.

Thanks for your help!

Charles

Is it any harder to maintain the vacuum in a large chamber than in a small chamber? I spoke with a chemical geologist about this and he thinks it is.

Now, as to why I'm even asking this question, there's a type of fusion reactor being developed whose power scales exponentially with its radius. His qualm about the engineering of such a thing is that the vacuum would be increasingly difficult to maintain. However, I don't recall that being an issue in, e.g., the ITER research reactor, or tokamaks of a similar order of magnitude. And I don't see how there would physically be a difference.

Any ideas as to what could be the mechanism for increased issues for larger sizes?

Thanks!

Charles

The Rayleigh-Jeans approach to standing waves in a perfectly-absorbing cavity has nodes at the walls to satisfy the boundary condition that there's no electric field there.

I didn't take second-semester E&M, so I'm a little confused as to why this requirement is needed. Does it have to do with the cavity's being a blackbody--i.e. not reflecting at all?

I take it that the reason the cavity needs to be perfectly non-reflecting is b/c the overarching question is what the frequency distribution of the E&M waves off a warm body are (so that we can tell what temp a star is just by its color, e.g.). So I hope I'm right on that and that that's not where my misunderstanding lies...

Related, why would anyone think that equal frequencies get equal probability? Planck kept that assumption, yet when we get into QM, we're not dealing in standing waves anymore. We're dealing in photons. So I don't see how Planck's prediction survived. Just seems misguided. Is this one of those phenomenological approaches that, like the Bohr atom, don't give understanding but instead are a historical stepping stone to better theories later on?

Thanks!

Charles

Hi,

Talk Origins is a site that serves as a repository for hundreds of well-informed arguments on the subject of evolution, creationism and intelligent design. Its articles were compiled from the newsgroup by the same name.

Is there a similar online repository for global warming?

Thanks,

Charles

It's said that like attracts like, and that this applies to both polar and nonpolar molecules. The mechanism for attraction between polar molecules is obvious, but what about nonpolar? Why would they attract each other? Van der Waals forces? But that can't be. If it was, then polar molecules would be attracted to them even more. Or am I misleading myself by not taking into consideration the time-varying nature of charge distribution in Van der Waals forces?

I was instructing a student yesterday, and wanted to have an answer to my own question for him, but couldn't come up with anything. Let me know, since "nonpolar attracts nonpolar" isn't exactly a searchable phrase in a textbook index.

Thanks!