Kräfte

Kräfte, the German term for forces, are interactions that cause changes in the motion or shape of objects. They have magnitude and direction and are treated as vector quantities. According to Newton's laws, the net force acting on an object equals the product of its mass and acceleration (F = ma) for constant mass. When the net force is zero, the object maintains a constant velocity or remains at rest (mechanical equilibrium).

Kräfte can be classified as contact forces (friction, tension, normal force, thrust, buoyancy) or field forces (gravitational, electric, magnetic). The four fundamental interactions describe forces at the smallest scales: gravity, electromagnetism, strong nuclear, and weak nuclear forces. In quantum theories, forces arise from the exchange of gauge bosons—photons for electromagnetism and gluons for the strong interaction—while gravity is described by general relativity, with a quantum description under development.

The resultant of several forces is found by vector addition, following the superposition principle. Forces determine acceleration via F = ma; in rotating bodies, a force applied at a distance produces torque, the rotational effect that depends on the lever arm and force. This torque leads to angular acceleration proportional to torque divided by the moment of inertia. Equilibrium requires zero net force and zero net torque.

Everyday examples include gravity pulling objects downward, friction opposing motion, normal forces from surfaces, buoyant forces in fluids, and electromagnetic forces that govern atomic and molecular interactions.