rotmassan

Rotmassan is a term used in Swedish technical literature to denote the inertia of a rotating body with respect to a specified axis. It reflects how mass is distributed relative to that axis and is closely related to the standard concept of moment of inertia; in many contexts rotmassan is used interchangeably with the moment of inertia, though some texts distinguish it as a practically measured or design-specific scalar representing the rotational resistance around the chosen axis.

The word is a compound of rot (rotation) and massan (the mass) in Swedish.

For a system of point masses, rotmassan about an axis is I = Σ m_i r_i^2, where r_i is the perpendicular distance from the axis. For a continuous body, I = ∫ r^2 dm. In general, the body’s inertia is described by an inertia tensor, and rotmassan about any axis is the quadratic form u^T I_tensor u, where u is a unit vector along the axis.

The concept is used in the design and analysis of rotating machinery such as motors, turbines, flywheels, and gears. It informs calculations of angular acceleration, energy storage, balancing, and dynamic response. Rotmassan is central to the formula for rotational kinetic energy, KE = (1/2) I ω^2.

Related topics include moment of inertia, inertia tensor, rotational dynamics, and rotor balancing.