Pallokappale

Pallokappale is a Finnish term used in physics, engineering, and education to denote a spherical particle or ball-shaped object. It serves as a simple, rigid body model for studying motion, forces, and collisions. In mechanics and kinetic theory, a pallokappale typically has a definite mass m and radius R, and is assumed to have uniform density unless stated otherwise. For a solid sphere with uniform density, the moment of inertia about its center is I = 2/5 m R^2, while for a thin hollow sphere it is I = 2/3 m R^2. When subjected to forces or torques, the motion can be described by translational equations for the center of mass and, if needed, rotational motion about the center.

In collision problems, pallokappale are used to model interactions with a coefficient of restitution e, which characterizes the relative speeds after impact along the line of centers. In statistical mechanics and kinetic theory, systems of pallokappale are often referred to as hard-sphere models, where particles interact only upon contact and do not deform.

In materials science and simulations, the pallokappale concept provides a straightforward representation for granular materials, powders, and colloidal suspensions, as well as a teaching tool for basic dynamics, momentum conservation, and energy transfer. The term is commonly found in Finnish textbooks and lectures dealing with classical mechanics and statistical physics. See also hard-sphere model, rigid body dynamics, collision theory.