 Body force

A body force acts throughout a body's or fluid's volume, rather than only through its surface. Gravity is the example used in hydrostatic pressure: a gravitational field $\mathbf{g}$ gives force per unit volume $\rho \mathbf{g}$, where $\rho$ is the mass density. More generally, a body force per unit mass $\mathbf{f}$ contributes $\rho \mathbf{f}$ to momentum conservation. Forces from electromagnetism are another example. Surface pressure forces produce buoyancy on an immersed body, while its body force from gravity acts downward.

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.