MDJH

Not sure whether to post this here or in the physics board, but I will post it in both for now. I have been falling severely behind in physical oceanography and optical physics. I got an exam on the former in 6 days, an exam on the latter in 11, and I would appreciate suggestions for advice on cramming either of them, especially on where to go for online tutorials. (I have found that MathTV sometimes helped save my neck in math cramming.)

I meant to link to it in the original post. Yeah, I multiplied f by pi and by r, but forgot to multiply by 2. That's a pretty big mistake. I suppose I should remove and replace the comment, then.

So basically I posted the following analysis as a comment on this cat video on youtube. "At about 2 minutes in, the fan circles 4 times in 5 seconds. That's 0.8 cycles per second. If we assume the cat's spinning an average distance of a metre from the centre of the fan, that means it's moving at 2.5 metres per second. (v=2*pi*f*r) Also, the circular acceleration would be (v*v)/r, which would mean a velocity change of 6.25 metres per second every second. And so, to the cat, the pull of the rope probably feels like two thirds of the pull of gravity." What say you, Science Forums? Is my analysis valid?

So I was thinking about the idea that light is pulled by gravity... if my understanding (the analogy of light in an accelerating elevator being treated as equivalent to light accelerating due to a force acting on it) is close enough to accurate my logic here should work. Ok, so basically energy is proportional to the product of mass and the square of the speed of light; this resembles the formula for centripetal force, which is proportional to the product of mass and the square of the speed of light, except also divided by the radius of the circle. So according to this logic, the centripetal force that pulls on a photon of light would be proportional to the ratio dividing the energy of the photon by the radius of a hypothetical circle it would be spinning in. This in turn suggests that said radius would be proportional to frequency of the photon, and inversely proportional to the gravitational force. Therefore, how sharp the bending of the light is depends not only on the gravity, but also on how low-frequency the light is. Would I be correct in assuming, therefore, that given approximately equal gravitational forces on each, a longer-wavelength photon would be more easily pulled in by gravity than a shorter-wavelength photon would? Is this why morning/evening sunlight is safer than early-afternoon sunlight?

This fall I plan on doing a physics course which uses Mathematica; more specifically, a mechanics course involving differential equations. Some, but not many, of the computers on campus have Mathematica installed on them, so if I were to use Mathematica outside of class time, I would need to either have access to those computers, or to have access to Mathematica at home. I do not plan on buying the actual program, (I have not completely ruled that out though) but I have heard that they offer a trial version that lasts two weeks; if I start now this should give me time to familiarize myself with Mathematica before the semester starts, making that physics course a little bit easier. This raises a couple questions: 1. Is the windows version of Mathematica enough like the mac version that practicing with one can help me use the other? 2. Is it best to practice Mathematica BEFORE the semester starts, or to wait until the semester DOES start so that I will be able to practice it AFTER classes for the first couple of weeks? (Or to wait until the middle of the semester, or near the end of it, etc...)

Let's say someone were holding an object (like a pencil) at a position away from the centre of mass, such that it would rotate from the gravitational torque if held still. Would there be a way to spin it (as in, about an external axis, while the line from the centre of mass to the pivot is in the same direction as the radius) such that the torque from the centripetal acceleration would just cancel out the gravitational torque?

Ok, so with electricity we have a charged particle creating an electric field, wherein a test charge further from a field-generating particle has a higher potential energy than a test charge closer to it, and so far this is analogous to gravity, in which case we have an object creating a gravitational field, and a test mass further from it has a higher potential energy than a test mass closer to it. In electricity, the test charge's ratio of potential energy to charge is known as electric potential. In gravity, I assume that analogous to this would be the ratio of gravitational potential energy to mass for a test mass, which would be the product of the gravitational constant and the distance from the centre of the source of the gravitational field. Would I be correct in assuming this? Furthermore, this suggests that the gravitational equivalent of voltage would be the difference in the gravitational potential over a distance, and hence would be proportional to whatever difference there would be in gravitational constant and whatever difference there would be in distance from the centre... but since gravitational constant itself is a function of distance from the centre, would it be redundant to include?

Seeing as how the extent to which we could stop it is already in dispute, I would think it would be more practical to try to adapt to it instead.

But would both motions tend to come to a stop at the same time, or at different times?

Ok, so supposedly white light is a combination of red, green, and blue light... but programs like MS Paint treat it like the amount of light goes from 0 to 255; in theory, could brightness of light be infinite? If so, would that imply that brightness of the components would be infinite? If so, then, would a better representation of light be a 3-dimensional graph, wherein one axis represents the intensity of red light, another the intensity of green light, another the intensity of blue light... and based on the intensity values for these three component colours, a position in 3-space on the graph would represent a particular colour, so as for colour to be seen as a linear combination of red, green, and blue light?

Ok, so first off, angular momentum doesn't need to involve rotational motion, and a particle can have "angular momentum" with respect to an axis if it is moving in a straight line that doesn't pass through the axis, right? Also, if the particle had a constant speed and constant mass, then moving along the axis, its angle with respect to the axis would be perpendicular when the distance TO the radius is the lowest... does this imply that the angular momentum of such a particle would be constant? Also, as for the angular momentum of something thrown into the air... let's say we had a water bottle that was filled part way. It was thrown into the air such that its plane of rotation was parallel to the long end of the bottle. While the bottle would be rotating, the water itself would be moving from one side to the other, and flowing along the edge on the way. Would the moment of inertia in such a case be constant or changing, and as such, would the angular velocity (assuming angular momentum is constant; neglecting influence of air friction) itself be a function of time while the bottle is in the air? And another thing, presumably air friction would act to slow down a rotating object, since air molecules are constantly in random motion and the number of collisions with air molecular will be higher in the direction of motion than away from it, right? And if an object were rotating AND translating, would friction stop both rotation and translation at the same time, or could it stop one before stopping the other?

So supposedly angular momentum of a system is conserved, right? Well, consider this video: If, hypothetically, the cat jumped while the roomba was rotating, would the cat be spinning at an angular velocity equal to whatever the angular velocity of the rotating roomba was when the cat jumped?

I wasn't saying it was CENSORED. Again, the concern is that the influence of the dairy industry might be part of the reason milk is even considered a health food in the first place.

Who's "we"? From my recollection of the article, it argues that some of the medical community HAS noticed, and that the influence of the dairy industry tends to suppress such findings. If you're referring to the general public, how on Earth is the average person supposed to know if something everyone consumes, that they're told is healthy, is a major contributing factor in common diseases?

Are you suggesting that the pharmaceutical industry deliberately avoids curing this disease to keep type 1 diabetics like myself dependent on insulin? If so what proof do you have? And as for diabetes research being underfunded, Marat, do you mean in comparison to other diseases, or disease research in general to the war on drugs?