Moment of inertia Definition and 1000 Threads

Homework Statement We did this question today in class, but looking back at it, I'm kind of confused. Two identical dumbbells are formed by placing equal point masses at either end of two identical light (ie. massless) rods. The rods are pivoted so that dumbbell A rotates around the centre...

I was wondering why we can not always assume the mass of a body to be concentrated at the Center of Mass and then multiplying the total mass by the square of the distance from center of mass to the axis,while calculating the moment of inertia of a body.(I found this question in University...

How do we find out that the moment of inertia about the hinges of a door with a width w is I=M w2/3. I find it like this in a book and also in table for the moments of inertia of homogeneous rigid objects with different geometries (about a long thin rod with rotation axis trough end). Thank you.

Homework Statement A system is given below. Pulley A has radius R and mass 2M and pulley B has radius 1/2 R and mass M. If the pulley is assumed as solid cylinder, find the acceleration of each object Homework Equations τ = I.α F = m.a a = α.R The Attempt at a Solution Equation of...

Homework Statement Solid slab with moment of inertia 2 kg m2 is given the forces as shown. Find the angular acceleration if θ = 37°, R1 = 10 cm, R2 = 25 cm Homework Equations τ = I . α The Attempt at a Solution This is what I've tried although I don't know it is correct or wrong; I tried to...

Prompt: Find the moment of inertia about the z-axis of the hemispherical shell of problem II-6. Additional Info.: -Problem II-6 states: the distribution of mass on the hemispherical shell z=(R^2-x^2-y^2)^1/2 is given by o(x,y,z) = (o/R^2)(x^2+y^2) where σ0 is a constant. Find an expression in...

Homework Statement I'm trying to work out the moment of inertia for this L shaped beam: http://dl.dropbox.com/u/630750/Screen%20Shot%202011-12-31%20at%2017.54.34.png Homework Equations (Included on my sheets below( The Attempt at a Solution I've made two attempts, the first...

Homework Statement Find the moment of inertia of a paraboloid f(x,y)=x^2+y^2 whose density function is ρ(r)=cr=dm/dv. use mass M and height H to express your answer 2. The attempt at a solution I took the double integral ∫∫r^2 ρ r dr dθ to find the I of a single disk as a function of r...

Similar to my other thread https://www.physicsforums.com/showthread.php?t=557750 I think in this case I need to use triple integrals But what is the integrand and limits? Can someone please help me set it up? Here's all I know ∫∫∫dydx Please help I have my final next wednesday.

I want to find the rotational energy of the sun. Erot=1/2*I*ω2 m=1.9891*10^30 kg r=6.955*10^5 km When I am using the formula for a sphere's moment of inertia: I=2/5*m*r2 I'm getting 3.848671797*1047 km*m2 Can i find the moment of inertia in another way? the moment of inertia needs...

Homework Statement There is a wheel with spokes rotating on a horizontal axis about its center. the Wheel has a w(omega) of 6∏ and a radius of .04meters there is a bug on one of the spokes at exactly 1/2 radius or .02meters. the bug has a mass of .005kg. Homework Equations not really sure...

Hello! I'm trying to derive the formula for the moment of inertia of a solid sphere, and I keep running into a strange solution. I set up the infinitesimally mass of an infinitesimally thin "shell" of the sphere: dm = 4\rho\pir2 dr And then solved for the moment of inertia: I = \intr2dm =...

Homework Statement A small sphere of mass 2.0kg revolves at the end of a 1.2 m long string in a horizontal plane around a vertical axis. Determine its moment of inertia with respect to that axis. Homework Equations Moment of inertia for sphere= (2/5)mr^2 The Attempt at a Solution...

I've just been thinking about moments of inertia in n dimensions and I just want to establish if this makes any sense: I'm considering doing a Monte Carlo evaluation of the moment of inertia of any n-ball - a solid sphere in n dimensions. Now I think you can say that the moment of inertia of a...

Hi everyone Homework Statement I want to find out the moment of intertia tensor of the graphic below. Homework Equations parallel axis theorem The Attempt at a Solution We know the moment of inertia for one sphere, that's given, so I don't have to calculate it...

Homework Statement Find the moment of Inertia of a cube (mass M, length L) around an axis going through one of the edges. Homework Equations I=Ʃmr2 The Attempt at a Solution Well I imagined the cube is formed of infinitely many square plates. The width of the square plate is dL...

Steel Joists: Moment of Inertia? I thought it might well be worth while asking here, as the Forum is awash with knowledge about most things. I am planning to do a loft conversion and I need to know about the strength of steel beams (Universal Joists, in fact). I keep seeing the expression...

Homework Statement A solid door of mass 39.30 kg is 2.34 m high, 1.68 m wide, and 3.23 cm thick. What is the moment of inertia of the door about the axis through its hinges? If the edge of the door has a tangential speed of 76.5 cm/s, what is the rotational kinetic energy of the door...

Homework Statement A cord 3.0 m long is coiled around the axle of a wheel. The cord is pulled with a constant force of 40N. When the cord leaves the axle, the wheel is rotating at 2.0 rev/s. Determine the moment of inertia of the wheel and axle. Neglect friction. (Hint: The easiest solution is...

Homework Statement Consider a rod of length L and mass m which is pivoted at one end. The moment of inertia of the rod about an end is Irod = 1/3 mL2. An object with mass m is attached to the free end of the rod. Find the moment of inertia of the system with respect to the pivot point...

Homework Statement Given that the conical shell has uniform density and thickness is made of one sheet, has mass M, height h, and base radius R, derive the moment of inertia about its axis of symmetry. Homework Equations I = MR^2 for a ring about its central axis. I = ∫dI - my approach The...

A small 750 g ball on the end of a thin, light rod is rotated in a horizontal circle of radius 1.2 m. (a) Calculate the moment of inertia of the ball about the center of the circle. (b) Calculate the torque needed to keep the ball rotating at constant angular velocity if air resistance exerts...

Homework Statement A solid cylinder of mass 0.600kg is released from rest and allowed to roll down a board that has an incline of 30degrees to the horizontal floor. If the solid cylinder is released 0.60m above the floor, what is the cylinder's linear speed when it reaches the lowest end of...

Moment of inertia help! I have a question about moment of inertia. How do you calculate an object that is away from the axis of rotation? I am trying to figure out how to find the total angular momentum of two disks. One disk is rotating around the origin. Disk 2 is connected to disk 1 and...

Homework Statement A sheet of plywood 1.81 cm thick is used to make a cabinet door 49.1 cm wide by 76.5 cm tall, with hinges mounted on the vertical edge. A small 181-g handle is mounted 45 cm from the lower hinge at the same height as that hinge. If the density of the plywood is 550 kg/m3...

Homework Statement Its actually not a homework , i am just curious about this I have disc with a hole in middle , R1 is inner radius , R2 is outer radius , Mass M is the disc's mass . Let density of disc uniform . I did it this way . - λ.dA=dm λ.pie.r.dr=dm as Area=pie.r^2...

I know that for for solid disks, the inertia is equal to (1/2)mr^2 and for hoops is just mr^2. This only works for if the mass is evenly distributed around though. So what about when the mass isn't equally distributed? How would you solve for the moment of inertia of a hollow disk if a small...

Homework Statement Not really a HW problem (no diagram), I just need to figure out this number for a design. I have an axle with two crank arms attached to either end, pointing in opposite directions. The entire thing will spin. I need to find the equivalent moment of inertia of the axle...

Homework Statement A 32kg door that is 107 cm wide. What is the moment of inertia 10 cm inside the door with rotation around a vertical axis? Homework Equations L=Iω The Attempt at a Solution I=1/3mL^2 I= Icm+ md^2 1/3(32)(107)^2 Im not sure what to do after I find the I...

So here I just need help understanding a concept. I was reading this website's derivation of the moment of inertia of a solid sphere here: http://hyperphysics.phy-astr.gsu.edu/hbase/isph.html#sph3 For the life of me I can't see where the (1/2)y2 term comes from. I would understand y2 because...

Homework Statement A grandfather clock uses a physical pendulum to keep time. The pendulum consists of a uniform thin rod of mass M and length L that is pivoted freely about one end, with a solid sphere of the same mass, M, and a radius of L/2 centered about the free end of the rod. Obtain...

Homework Statement Two forces are applied to a pulley with a moment of inertia I = .15kg*m^2. The pulley is mounted so that its frictionless axle is fixed in place. 1) What is the angular acceleration of the pulley? 2) If the pulley starts from rest, how long does it take to undergo...

Homework Statement What is the moment of inertia of an 8 kg, 40 cm diameter disk for rotation through the edge of the disk? Homework Equations I = \frac{1}{2}MR^2 The Attempt at a Solution Inertia at the center of the disk would be I = \frac{1}{2}MR^2, right? I'm not sure what...

Homework Statement [FONT="Comic Sans MS"]A light string is wrapped around the outer rim of a solid uniform cylinder of diameter 75.0 cm that can rotate without friction about an axle through its center. A 3.00 kg stone is tied to the free end of the string, as shown in the figure . When the...

Homework Statement a)Evaluate ∫∫∫E dV, where E is the solid enclosed by the ellipsoid x^2/a^2+y^2/b^2+z^2/c^2 =1. Use the transformation x=au, y=bv, z=cw. b)If the solid in the above has density k find the moment of inertia about the z-axis. Homework Equations ∅=phi The Attempt...

Homework Statement A stiff uniform wire of mass M0 and length L0 is cut, bent, and the parts soldered together so that it forms a circular wheel having four identical spokes coming out from the center. None of the wire is wasted, and you can neglect the mass of the solder. What is the...

[b]1. Homework Statement A particle of mass can slide without friction on the inside of a small tube bent in a circle of radius r. The tube can rotate freely about the vertical axis, x3, and has a moment of inertia I3 about this axis. Homework Equations a) Derive the Hamiltonian for...

I have been playing with several vehicle dynamics simulators for a while now, and many of them require vehicle inertial properties to create realistic simulations. There is very limited published data out there so I was wondering how could one calculate these properties experimentally...

Homework Statement The distribution of mass on the hemispherical shell: z=(R2-x2-y2)1/2 is given by σ(x,y,z)=(σ0/R2)(x2+y2) where σ0 is a constant. Find the moment of inertia about the z-axis of the hemispherical shell. Homework Equations I=∫r2dm The Attempt at a Solution...

Homework Statement Find the moment of inertia of a right circular cone of radius r and height h and mass m Homework Equations I = ∫r2 dm V = 1/3*π*r2*h The Attempt at a Solution Assume density is p dm = p dv divide both sides by dr dm/dr = p dv/dr dm/dr = p (d/dr * 1/3*π...

Hi Physics Forums! Moment of inertia question for you: I have a cuboid, like the first one in this link http://en.wikipedia.org/wiki/List_of_moments_of_inertia only it is curved around the y (w in pic) axis such that the x (h in pic) axis touches the top and bottom ends of the cuboid...

Homework Statement [PLAIN]http://www.smartphysics.com/images/content/mechanics/ch15/momentofinertia2new.png What is the moment of inertia of the object about an axis at the center of mass of the object? (Note: the center of mass can be calculated to be located at a point halfway between the...

Homework Statement See below for the diagram. Use this result to calculate the moment of inertia of the shape below about the axis shown by the dashed line. The object is a square with a side of length L, total mass of 4M, and a uniform density. Homework Equations The Attempt...

Homework Statement A uniform disk of radius R is cut in half so that the remaining half has mass M. (Figure (a)) 1. What is the moment of inertia of this half about an axis perpendicular to its plane through point A? Express your answer in terms of the given quantities. 2. Why did...

Homework Statement I was trying to find the moment of inertia of a rectangle with width a and height b were axis of rotation is through it's center of mass Homework Equations The Attempt at a Solution I = integral r^2 dm rho = dm/dA dm = rho dA If I take an infinitely small...

Homework Statement A hole of radius R/2 is cut from a solid sphere of radius R. If the mass of the remaining plate is M, then moment of inertia of the body about an axis through the centre is____. Answer:57/140*M*R^2 Homework Equations Moment of inertia of solid sphere is...

Moment of inertia of a "music triangle" Homework Statement Find the moment of inertia about an axis thru the centre of mass, perpendicular to the plane of an equilateral triangle consisting of identical rods of length 'l' and mass 'm' connected at their ends. Homework Equations...

hey, I want to ask you something about to calculate the moment of inertia for any shape. My problem is that I can not calculate that moment of inertia values for any shape. Such as rectangle or stick and the others. I have tried to calculate for stick and I have found the solution of...

Homework Statement Suppose I have a book with dimensions 24 by 27 cm and its being pivoted at one of its corners so that it can swing along a plane parallel to itself. I'm supposed to find the period. But in order to do that I need to know its moment of inertia, would I have to write an...

Hey I just finished an experiment in my physics lab where we examined the precession and nutation of a gyroscope. The gyroscope was built with a shaft which had a pivot in the middle, on one end of the shaft the large spinning disc was placed and on the left side of the shaft...