Moments Definition and 598 Threads

Hello all, Since I have run into the problem of regularly leaving moments out of my free body diagrams (and vice versa), I thought I'd pose a question on the topic. In trying to wrap my head around the concept, I've gone back to the beginning of the semester's notes and that didn't really...

Hi everyone. I have this problem and I don't even know how to start it! If you are familiar with my previous posts, you know that I usually have most of a problem completed before posting here with my difficulties, however, I cannot even start this one! I don't think there is enough...

This question is bugging me and though from my point of view it doesn't make sense I'm hoping that someone else can see my thinking and tell me whether they agree with it or not (because this is about the fourth question I've had to say that I can't solve this because the book is talking BS)...

Derivation of the principle of moments... i know the principle of moments might seem very obvious at the beginnning... but really, how was it derived or proposed? and by what proof?

can anyone tell me how to find moments of inertia for the centre point of a semicircle??

When you calculate the two moments for the law of the levers, they are supposed to be the same, right?

Hello everyone, I'm working on a basic spaceflight simulator during the break, and I've been unable to come up with some info I need to do the physics. Suppose you have a simple object... say, a beam of dimensions w, h, and d. Then suppose (for example) you apply a constant force at the...

once again I have succeeded in confusing myself about basic angular motion...:confused: If I have a pulley of with an unkown moment of inertia, and a bucket hanging from the pulley with a known mass, height, and acceleration in which it falls. Why can't i use: Torque = Ia rf = Ia r * mg...

Could someone direct me to a site that explains how the common moments of inertia were arrived at? My physics professor put up on the board today that for a uniform sphere: I=\frac{2}{5}mr^{2}. He said it was just the anti-derivative of something, but he didn't want to go into it because...

Part of my lab involves using the method of moments to calculate the weight of a meter stick. We attached two weights to different ends of the meter stick and are expected to calculate the weight of the meter stick based on the positions of the weights. I have no clue what the moment of methods...

using "primitives" to integrate moments of Inertia My classmates are lost and I just can't think the way my proffessor does when approaching these problems. He gave us about 50 shapes to find moments of inertia for this weekend and I'm not having any trouble doing them... my way. I can use a...

ok, X_1,X_2,...,X_n are independant(and unbiased) rectangular distributed random variables over the interval [0,a] It is known that T(X)=max(X_1,X_2,...,X_n) is sufficient. i am supposed to find the moment estimator for a using the method of moments. i know I'm supposed to equate the first...

Check my Moments... Edit: Deleting post because I think quite a bit of my work was incorrect--will repost tomorrow, corrected, hopefully...

mass of e is 100 kg mass of bar is 20 kg and acts at midpoint sume of moments about point a due to weight of bar and forces on b by bc, bd, and be, are 0, determine tensions in bc and bd so i continued like this. The moment about point A from all those forces is 0. 0 = (Raf x Wab) + (Rab...

I have a mechanics question that I can't seem to figure out. I've spent quite a bit of time on it but don't have much of an answer. If anyone can help I would appreciate it. Round objects are rolling without slipping down an inclined plane of height H above the horizontal. The box is...

Hello, I have a question concerning the GMM equation specification. Say we partition each day in 7 intraday intervals. We want to estimate the 7 intraday interval moments for a variable Y observed in those 7 intervals over a period of T days meaning we have t = T*7 total observations for...

Hi i was wondering, if the sphere is divided into 5 spherical shells, each shell has a different density and each shell is of equal thickness My question is: Can I calculate the moments of inertia for each shell by subtracting the moment of inertia of the sphere inside it, from the entire...

I found the following question in a textbook: Two men are carrying a uniform ladder of length 12m and weight 250N. One man holds the ladder 2.0m from the front end and the other man is 1.0m from the back of the ladder. Calculate the upward contact forces that each man exerts on the...

Hi can someone please do part ii) of this moments question. Just can't get my head round it. Thnx! http://img150.echo.cx/img150/872/physicspaper0128xk.jpg http://img150.echo.cx/img150/1093/p...paper0130ot.jpg

I'm having a lot of difficulty calculating the monopole and dipole moments for a dielectric sphere with surface charge of the form, sigma(theta)=sigma(0)cos(theta) If surface charge wasn't present and it was just a point charge I would be OK but I need a few pointers on how to do it with...

I'm stuck! This is the question: A uniform rod AB has length 3m and weight 120N. The rod rests in equilibrium in a horizontal position, smoothly supported at points C and D, where AC=0.5m and AD=2m. A particle of weight W Newtons is attached tto the rod at a point E where AE=x metres. The rod...

maybe I'm missing some stupid algebraic mistake..but given theta/theta + 1 = y. how does this imply that the method of moment is theta = y/ 1-y??

Hi, I have my first year university exam coming up soon and this type of question seems to feature quite prominently in the past paper questions we are given where I have to take moments about a point and also resolve forces horizontally and vertically. I suppose the best way to show you would...

One moonlit night (the night of October 16, 1843 to be precise), as William Rowan Hamilton took a romantic stroll with his wife over the Brougham Bridge in Dublin, Ireland, the fundamental relationship of quaternion multiplication came to him in a flash of genius (i^2=j^2=k^2=ijk=-1)...

I recall that the shape of an i-beam is near optimal because of its moment of inertia. Does any have a reference that shows this, with explanation?

I've been told that there are useful interpretations of the ratios of moments of probability density distributions, such as <x^4>/<x^2>. I only have un-normalised values of the second and higher moments of the distribution of interest. Is there any way of quantifying the spatial extent of the...

i'm learning the method of moments and I'm not understanding on how to do it. so for example, fy(y, theta) = theta*y^(theta -1). 0<=y<=1. to find the method of moments estimate for theta. the book does E(y) = the integeral from 0 to 1 of y * theta*y^(theta-1) dy. and that becomes...

Hi, can anyone help me understand how to find the moments of inertia for the following: 1- A triangular lamina (isosceles) of mass M, base 2B and height H. about line of symmetry. 2- A uniform lamina of mass M, bounded by the curve with equation y²=4ax and the line x = 4a about the x-axis...

Hi there, I was hoping that someone here could maybe give me a hand with a couple of issues I'm having to do with moments of inertia. For a right circular solid cone of mass m, height h and base radius a, we have to show that its moment of inertia about a line through its vertex and...

in the context of the lever, archimedes is recorded as saying ''give me a long enogh lever and i will move the earth'' explain in terms of moments the point archimedes was making how can i tackle this question?, i know the principle of moments the sum of the clockwise direction=the sum of...

Okay, we all know that TV is the spawn of satan and that no thinking person would be caught watching that garbage. With that said, what are your favorite or most memorable shows, skits, plots, one-liners, moments, or events. Personally, I was a complete TV kid and still am. I really watch...

Pivot point on a Uniform Rod and Acceleration I'm stuck on this question, which seems like it should be fairly simple: A uniform rod of length 1.15 m is attached to a frictionless pivot at one end. It is released from rest from an angle theta = 21.0° above the horizontal. Find the magnitude...

A uniform thin solid door has height 2.20 m, width .870 m, and mass 23.0 kg. Find its moment of inertia for rotation on its hinges. Is any piece of data unnecessary? So far, I don't understand how to calculate moments of inertia for things like this at all. I can do a system of particles...

Hi! I am working on this problem: A solid circular disk has a mass of 1.2 kg and a radius of 0.17 m. Each of three identical thin rods has a mass of 0.16 kg. The rods are attached perpendicularly to the plane of the disk at its outer edge to form a three-legged stool. Find the moment of...

The problem is: Three identical thin rods, each of length L and mass m, are welded perpendicular to one another. The assembly is rotated about an axis that passes through the end of one rod and is parallel to another. Determine the moment of intertia of this structure. Ok what I know is...

Hello, My question is fairly simple. My instructor solved in class today Laplace's equation in spherical coordinates which resulted in spherical harmonics. I have not taken any quantum mechanics yet so this is my first exposure to spherical harmonics. What do the "l" and "m" terms in the...

A copper(II) ion fits perfectly into the center of tetraphenylporphyrin (TPP), and i was wondering if by doing so, will it become more polar or less polar than the original TPP? this is something that i forgot, but can someone please correct me if i am wrong? if a molecule has no dipole...

Hi all, Why are there so many moments of inertia for a given section? That is, i come across moments about the origin, x-axis, y-axis, centroid, xy-axis...etc... What are the differences? are there typical applications? Please point me in the correct direction Thanks in advance, any...

Hello all. I'm not sure if this is the correct forum because I'm in the UK and I don't know what "Grade K12" is, but the sort of stuff in this forum seems to be the type of work we're doing. We've just started some work on moments and equilibrium and I'm having difficulty solving the...

Do lone pairs in a molecule have dipole moments? and does net dipole always go in the direction of the lone pairs?

We all know friends is over. What is the funniest-memorable scenes-lines ? :smile: :smile: :approve: :wink: :biggrin: :-p

I am having trouble getting to grips with moments and couples and i have got stuck on the following question: "A uniform horizontal rod AB is 120cm long and weighs 250N. It is supported by two veritcal wires, one 10cm from A and the other 20cm from B. Loads of 100N and 350N hang from the...

Hi! Does anyone know if there is a periodic table trend for the value of dipole moments...I tried looking it up on the internet and I haven't had any luck maybe someone in here knows..if you do please help! Thanks in advance!

I am currently learning about how to calculate moments of inertia of various shapes. I can calculate them fine using the Parallel Axis Theorem, but I am having some difficulty trying to understand the overall concept. Can somebody give me some practical applications of MOEs? I am also...

Hi all, I've been here before out of geneal interest but this is my first post, so i hope it's in the right spot. I have a problem that I need an answer to, unfortunately due to sickness i wasn't at school when we were taught the theory of moments (called torque by some). Anyway my...

In general, I=[inte]R2dm. First of all, what is R? R is the component of the position vector that is perpendicular to both the angular and linear velocity. Is this correct? EDIT: One more question. If we know the moments of interia of say two bodies, how do we find the moment of inertia...

I can't put it more simply than this: Please end this strange argument before I go mad over it.

This may be a sort of odd question. I know what a moment of inertia is. I know what they represent, I know how to use them, I even know how to calculate them from scratch if need be. But I don't know why they are what they are. Why is it that this weird value with seemingly random d^2...