Confusion Definition and 1000 Threads

I'm just a humble human being here, so if my question comes across as stupid, please forgive me! :) Newton's Third Law of Motion states that for every action there is an equal (in magnitude) but opposite (in direction) reaction. One of my A-level revision guidebooks state that the attraction...

http://imageshack.us/photo/my-images/440/49789320.png/ Assuming the indicated direction of motion, why is friction acting as shown in the tangential direction? Shouldn't it be acting in the opposite direction?

I am a bit confused. http://pokit.org/get/bedc0ac7e1d17e01d7d58b021b81663c.jpg The function is y=x(2t) and the point of it is to show the property of time-invariance.(which we should fail in this example, because it isn't time invariant.) Input signal is x1(t) Output signal is shown for...

Anyone who follows some of my posts knows I've fallen in love with GianCarlo Ghirardi's thought experiment. (apologises for the equations - I don't know how to work LaTeX). The experimental set-up is a 45 degree polarised photon goes through a birefringent crystal. On the other side of the...

1. Homework Statement Find the total charge on a circular disc of radius ρ = a if the charge density is given by ρs = ρs0 (e^−ρ) sin2 φ C/m2 where ρs0 is a constant. Are the two limits of integration from 0 -> a for ρ and 0->2∏ for φ? In the example given in the notes, ρ varies, instead of...

Bag contains 9 blue balls, 3 red balls. A ball is selected at random, colour recorded and NOT replaced. A second ball is selected at random, colour recorded. a) Draw tree diagram (no problem). Part 2 a) Find probability second ball is red (no problem, 0.25) b) Find probability both...

Folks, 1) If we have \int F \cdot dr that is independent of the path, does that mean that the integral will always be 0? 2) For 2 dimensional problems when we evaluate line integrals directly and use Greens Theorem for every piece wise smooth closed curves C, arent we always calculating...

People have written about mathematical creativity and the joy and beauty of mathematics. What about the sleazy underside of mathematics? Has anyone written essays about Mathematical Confusion? As I recall my teenage studies of mathematics, the most common experience was "getting stuck". I...

If I say, V = I x R V = 1 x 5 V = 5 volts Now, if I interchange the values V = 5 x 1 V = 5 volts When current is 1 amp and resistance was 5 ohms, the voltage was 5 volts. When I interchange the values then it is still 5 volts. How can I...

This is a general concern with finding temperature values at different processes in the cycle, however i do have an example i am stuck on, and can post that if needs be. anyway, if i was required to find the flow rate at outlet, which temperatures would i need to put in the SFEE as i know...

If I take the Dot Product of two vectors, say A and B, I get: AxBx + AyBy + AzBz And then when I add those terms, I get the magnitude, right? So when one of those terms are negative, that means I could end up with a negative magnitude? I thought magnitude had to be positive.

Hi, just a small doubt I'm having: I'm given a cross tabulation table, such as undernourished status versus gender of the child: -----------------------------undernourished -----------------------------yes--------no --------------------boy------37-------- 86 ---------gender...

So I am again stuck on a question I have been provided. The question is: Draw a FBD for each monkey. For each monkey, determine the rope tension that would allow the monkey to begin accelerating in the expected direction. (on a side note this is a pulley situation one monkey is 22kg and the...

Hello there. I'm new to the forums obviously. And I'm also quite new to physics. I've read many existing answers about how this works but I can't really understand how it would logically work out. From what I've understood. Gravity is not a force. Objects move in a straight line unaltered by...

I think I am missing the point of center of mass here but help me understand. So we calculate the gravitational acceleration on Earth with the Newton's law of gravitation equation, but what gets me confused is the fact that we look at Earth as a point mass. As Earth is "big and round", I...

This might be silly question for some people, yet better to ask than don't know the answer :(. so the thing is , i know that centripetal force holds a thing to keep running on a path, but when i think of Earth and all those planet which surround it, the centripetal force is gravity right ? and...

http://einstein1.byu.edu/~masong/emsite/S1Q50/EQMakerSL1.gif Hi guys, I have a little confusion about the Gauss' law in differential form over here, obviously, many textbook wrote it in the above form, but actually, the only place at which divE is not zero is at the locations where the...

If there is always an equal an opposite reaction, wouldn't everything always be in equilibrium and there'd be no net forces? If a car's exhaust is pushing back with xN, the car gets pushed forwards with xN. So the net force is 0 so how can there be acceleration?

Okay So, the question I have here is.. Masses are connected as shown. m1 = 5.0 kg and m2 = 4.0 kg. a) find the acceleration of each object and b) the tension in the two strings I have attached the picture example as well (as there is another unlisted weight in it) With pulley problem's I...

I just have one quick question on using direct calorimeters on humans, and it might be a dumb question but its got me a bit confused. From my understanding the calorimeter will measure the change in temperature of water from the heat that a person's body gives off. I understand that when...

Hi all, First off, not sure which forum maybe the most relevent, hopefully this one is the most suited? I do not have much of a background in maths, so bare with me. I am trying to implement a Modular exponentiation encryption method, I am using...

I curiously never had a problem solving Seperable Equations in the Seperable Equations chapter of the Boyce/Diprima book. I am the kind of person who likes to do things the long way, and encountered a problem solving for an Integrating Factor(Linear ODE, NOT EXACT) the long proofy way. I tend...

I had a problem a few days ago that involved a yo-yo falling. It was a disk with a string wrapped around it, and the string was attached at a certain height. In the explanation for the problem, it said the equation "weight - tension = ma" could be used to find the linear acceleration of the...

Homework Statement See first figure attached. Homework Equations The Attempt at a Solution For this question I understand parts 1) and 2) entirely and have obtained the correct answers from the solutions. I am confused about part 3) and I think my confusion stems out from...

Hi Recently performed a very basic fluid mechanics experiment with water flowing at different speeds through a Venturi Rig. Most of it went as expected, total head stayed roughly the same throughout but slightly decreased from flow loss due to resistant forces. However, at certain random...

Homework Statement Let's say an object is moving with x(t)= e^(-1/t^2) it's motion is continuous everywhere and differentiable because its exponential so v(t)= 2e^(-1/t^2)/t^3 a(t)= e^(-1/t^2) *(4-6t^2)/t^6 I have asked to a calculus teacher and he said all the derivatives will be 0 at...

Homework Statement See figure attached. Homework Equations The Attempt at a Solution If we attempt to solve part a) in this question we encounter several confusions. If we assume i(t) to be a positive current, the magnetic flux will flow through the core in a counter...

Homework Statement In a constant pressure process ant 1 bar determine how much heat must be added to raise the temperature of 2kg of compressed water at a temp of 50C so that it become superheated steam at a temp of 200C? u2=2659KJ/Kg Homework Equations W=-P(V2-V1) Q+W=U2-U1 The...

My physics book explains a van de Graaff in this way: A small conducting sphere of radius a and carrying charge q is located inside a larger shell of radius b that carries charge Q. A conducting path is momentarily established between the two conductors, and the charge q then moves entirely to...

I was reading in my chemistry book about significant numbers. Also about measured and exact numbers. From what I understand, a measured quantity can be different than an exact number. The book said when comparing something, like 1 lb = 16 oz, it is an exact number because the two are the same...

Higgs Confusion (The Higgs "Era") I thought I understood the basic concepts behind the Higgs mechanism (spontaneous symmetry breaking and such). But I've read a couple of sources that talk about the "Higgs Era" - the period shortly after the BB when the U was still hot/dense enough for the...

Homework Statement I am currently doing some Hooke's Law problems. While I do not have any trouble with any exercise in particular, I do have trouble with the sign in the equation. Let's say I have a vertical spring and I attached a hanging mass m to it. The string will then stretch a distance...

My professor introduced to us this concept, but when she was explaining it, I don't think she even knows what she is talking about. So I've come to ask people who know their stuff to help. I was told that on R2, the inequalities (1) x > 0, y > 0 Is open and unbounded (2) x \geq...

this example was in a book I bought ( maths methods for physics, Mathews and Walker) dy/dx + sqrt( (1-y^2) / (1-x^2) ) = 0 dy/(1-y^2) + dx/(1-x^2) = 0 sin -1 y + sin -1 x = c [1] or, taking the sine of both sides x (1-y^2)^1/2 + y...

Hi all, Just having some trouble understanding a certain example of cross product. It's actually for physics, but figured it belongs in this forum. In the question I am supposed to cross (dl)y hat with (x1)x hat. So I go (0 dl 0) x (x1 0 0) = (-x1dl)z hat. But turns out the answer the...

Homework Statement So basically I have plotted two variables I measured on a graph, which gives a simple linear relationship, and have found the gradient and standard error of the gradient (1.21251 and 0.03275 respectively). Now my problem is that this gradient is equal to a constant divided...

I attached the drawing. The problem state ment is to find the magnetic field at point P. the straight line segments cause no field. I have no problems with getting the numbers for this problem but I am confused about the direction. The solution manual says the field is out of the page, I don't...

Okay, so we did a lab in class with Na2CO3 in BaCl2 first. The reaction formed a white precipitate, and I suppose the products are BaCO3 + 2NaCl. Not sure if NaCl is dissolved or not, or if it was the white precipitate I saw, but anyways, here's my question... We added HNO3 to that new...

A statement in a book of analysis I have says: (Q,+, .) is a commutative ring with an identity element. I assume by its notation (Q,+,.) is a tuple.(correct?) There are several questions that come to mind: 1. Why is there an order between Q,+ and . ? 2. As far as I know, a tuple is an...

im a bit confused - please help - I am a complete beginner! I have several classes, within which are several attributes defined and declared. The assocation between some of these classes are aggregation, and between others is compostion. Take the example of person and car being and...

Hello Everyone! I have recently been attempting to understand negative resistance circuits(on a practical level at least to start). I've pulled up a few websites giving actual circuits to demonstrate the principle, but still can't quite understand it. Every circuit example so far shows either...

This is a really dumb question, but could someone quickly explain why it is that if b > a in the equation of an ellipse then y is the major axis. Just intuitively I want to think that y^2/5 as opposed to y^2/3 is going to be smaller for a given value of y since each value is being limited by...

Homework Statement Is is possible to have capacitor with one plate charge +Q and another charge -K, K≠Q. Homework Equations C=Q/ΔV. Because i wouldn't know what to substitute for Q.. The Attempt at a Solution I don't think it is possible for a capacitor connected to a single...

Homework Statement I am trying to understand the concept of short circuit with kvl laws it seems like i arrive at contradictory stuff http://imageshack.us/photo/my-images/38/shortcircuitr.png/ it seems like the voltage across the wire and resistor are equal by KVL however the current...

I'm currently in an introductory thermal physics course, and today we learned about the Boltzmann factor and how to use it to calculate various quantities with the corresponding probability distribution. All was going well until we got to the subject of paramagnetism. We supposed a system of...

I am reading a paper and the authors read the tt component of the metric from the line element ds^2=f(r)[g(r) dt^2+h(r) dr^2] as g_{tt}=g(r) instead of (what I expect to be) g_{tt}=f(r) g(r) Could somebody please explain to me why? Thank you.

Hello all, I was hoping someone would be able to clarify this issue I am having with the Lie Derivative of a vector field. We define the lie derivative of a vector field Y with respect to a vector field X to be L_X Y :=\operatorname{\frac{d}{dt}} |_{t=0} (\phi_t^*Y), where \phi_t is the...

I understand the use of this rule for the limit as x goes to 0, but not for the limit as x goes to infinity. Can this rule be used to find limits to infinity? How? I have googled this but couldn't find a good explanation.

I know power = Torque x angular velocity (rad/s) AND I am wondering if angular velocity can be calculated through strokes per minute? The product is a reciprocating saw (not orbital). In this case are RPM's the same as SPM'S? Thanks

Homework Statement A force which is at an angle θ to the horizontal (not being 90°) has two components Fx = FCosθ and Fy = Fsinθ along the x and y direction. However, when working out problems regarding objects on an incline, the horizontal (parallel to the slope) component of Normal force...