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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 moment of inertia, denoted by I, measures the extent to which an object resists rotational acceleration about a particular axis; it is the rotational analogue to mass (which determines an object's resistance to linear acceleration). The moments of inertia of a mass have units of dimension ML 2 ([mass] × [length] 2).
Rotating unbalance is the uneven distribution of mass around an axis of rotation. A rotating mass, or rotor, is said to be out of balance when its center of mass (inertia axis) is out of alignment with the center of rotation (geometric axis). Unbalance causes a moment which gives the rotor a wobbling movement characteristic of vibration of ...
This is simplest to express for the case of a single point mass, in which is a function (,), and the point mass moves in the direction along which changes most steeply. In other words, the momentum of the point mass is the gradient of S {\displaystyle S} : v = 1 m ∇ S . {\displaystyle \mathbf {v} ={\frac {1}{m}}\mathbf {\nabla } S.}
If a first body of mass m A is placed at a distance r (center of mass to center of mass) from a second body of mass m B, each body is subject to an attractive force F g = Gm A m B /r 2, where G = 6.67 × 10 −11 N⋅kg −2 ⋅m 2 is the "universal gravitational constant". This is sometimes referred to as gravitational mass.
Thus, ultimately, "inertia" in modern classical physics has come to be a name for the same phenomenon as described by Newton's first law of motion, and the two concepts are now considered to be equivalent. The effect of inertial mass: if pulled slowly, the upper thread breaks (a). If pulled quickly, the lower thread breaks (b).
F = total force acting on the center of mass m = mass of the body I 3 = the 3×3 identity matrix a cm = acceleration of the center of mass v cm = velocity of the center of mass τ = total torque acting about the center of mass I cm = moment of inertia about the center of mass ω = angular velocity of the body α = angular acceleration of the body
Assuming the mass of the torsion beam itself is negligible, the moment of inertia of the balance is just due to the small balls. Treating them as point masses, each at L/2 from the axis, gives: Treating them as point masses, each at L/2 from the axis, gives: