Moment of inertia of a stiff wire bent into a wheel with spokes

Click For Summary
SUMMARY

The moment of inertia of a circular wheel formed from a stiff uniform wire with four spokes is calculated using the equations for the rim and spokes. The total moment of inertia (Itotal) is derived from the rim's moment of inertia (Irim = MR²) and the spokes' moment of inertia (Ispoke = 1/3ML²). The correct mass distribution is determined by the relationship Mspoke = M0/(2π + 4) and Mrim = M0 - 4*Mspoke. The final expression for the moment of inertia is I = (1 - 4/(2π + 4)) * M0 * (L0/(2π + 4))² + 4 * M0/(2π + 4) * (L0/(2π + 4))².

PREREQUISITES
  • Understanding of moment of inertia concepts
  • Familiarity with the equations for rigid body rotation
  • Knowledge of mass distribution in composite shapes
  • Basic algebra for manipulating equations
NEXT STEPS
  • Study the derivation of moment of inertia for various shapes
  • Learn about the parallel axis theorem for composite bodies
  • Explore applications of moment of inertia in mechanical engineering
  • Investigate the effects of mass distribution on rotational dynamics
USEFUL FOR

Students in physics or engineering, particularly those studying mechanics, as well as educators looking for practical examples of moment of inertia calculations.

mcphyssics
Messages
2
Reaction score
0

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 moment of inertia of this wheel about an axle through its center perpendicular to the plane of the wheel? Express your answer in terms of the given quantities.

Homework Equations



Irim = MR2
Ispoke = 1/3ML2
Itotal = Irim + 4*Ispoke

The Attempt at a Solution



The length of one spoke, which should also be the radius of the rim, should be L0/(2\pi+4)

I am unsure of the mass of one spoke, as well as the mass of the rim. Would the mass of one spoke be the same ratio? (Mspoke = M0/(2\pi+4)) ?
If so, then what would be the mass of the rim? I thought Mrim = M0 - 4*Mspoke
therefore Mrim = (M0*(1-4/(2\pi+4))
but I am not getting it right when I submit it.
 
Physics news on Phys.org
What, exactly, are you submitting?
 
This is what I have: I = (1-4/(2\pi+4))*M0*(L0/(2\pi+4))2+4*M0/(2\pi+4)*(L0/(2\pi+4))2

It seems very messy/cumbersome. Am I going about this wrong?
 

Similar threads

Replies
8
Views
14K
  • · Replies 12 ·
Replies
12
Views
2K
Replies
11
Views
3K
  • · Replies 3 ·
Replies
3
Views
7K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 4 ·
Replies
4
Views
4K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 3 ·
Replies
3
Views
1K
Replies
6
Views
3K