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The moment of inertia depends on how mass is distributed around an axis of rotation, and will vary depending on the chosen axis. For a point-like mass, the moment of inertia about some axis is given by , where is the distance of the point from the axis, and is the mass. For an extended rigid body, the moment of inertia is just the sum of all ...
The moments of inertia of a mass have units of dimension ML 2 ([mass] × [length] 2). It should not be confused with the second moment of area, which has units of dimension L 4 ([length] 4) and is used in beam calculations. The mass moment of inertia is often also known as the rotational inertia, and sometimes as the angular mass.
The moment of inertia is the 2nd moment of mass: = for a point mass, for a collection of point masses, or () for an object with mass distribution (). The center of mass is often (but not always) taken as the reference point.
Similarly, for a point mass the moment of inertia is defined as, = where is the radius of the point mass from the center of rotation, and for any collection of particles as the sum, =. Angular momentum's dependence on position and shape is reflected in its units versus linear momentum: kg⋅m 2 /s or N⋅m⋅s for angular momentum versus kg⋅m ...
The second polar moment of area, also known (incorrectly, colloquially) as "polar moment of inertia" or even "moment of inertia", is a quantity used to describe resistance to torsional deformation , in objects (or segments of an object) with an invariant cross-section and no significant warping or out-of-plane deformation. [1]
Classical mechanics is the branch of physics used to describe the motion of macroscopic objects. [1] It is the most familiar of the theories of physics. The concepts it covers, such as mass, acceleration, and force, are commonly used and known. [2]
r cm is the position vector of the center of mass of the body with respect to the point about which moments are summed, a cm is the linear acceleration of the center of mass of the body, m is the mass of the body, α is the angular acceleration of the body, and; I is the moment of inertia of the body about its center of mass.
As a detailed example, ammonia has a moment of inertia I C = 4.4128 × 10 −47 kg m 2 about the 3-fold rotation axis, and moments I A = I B = 2.8059 × 10 −47 kg m 2 about any axis perpendicular to the C 3 axis. Since the unique moment of inertia is larger than the other two, the molecule is an oblate symmetric top. [8] Asymmetric tops ...