 Body force

A body force acts throughout a fluid volume. Gravity and electromagnetic forces are standard examples; a body force per unit mass $f$ contributes $\rho f$ to the momentum equation.

Body force refers to a force that acts on a body or object from within, rather than being applied at its surface. Unlike surface forces, which are exerted through contact (like friction or tension), body forces are distributed throughout the volume of the body. Examples of body forces include: 1. **Gravitational Force**: The weight of an object due to gravity acts as a body force, pulling it toward the center of the Earth. This force acts on every mass within the object.