Force acting on an object that acts on the volume of the object is a ______.

Force acting on an object that acts on the volume of the object is a ______.

• A. body force
• B. internal force
• C. external force
• D. surface force

Answer: (A)

The main idea is distinguishing forces that act through the whole volume of a body from those that act only on its surface or arise from interactions inside the body. A body force is a force density that acts on every material point inside the object, so when you sum (or integrate) over the volume you get the total force. Gravity is the classic example: every little volume element dV experiences a gravitational force rho g dV, and integrating over the entire volume gives the weight. This is different from surface forces, which act on the boundary surface (like pressure on the surface), or internal forces, which are forces between parts of the same body. External forces come from outside the object and can be either body or surface in nature, but the phrase “acts on the volume” uniquely identifies a body force.

The main idea is distinguishing forces that act through the whole volume of a body from those that act only on its surface or arise from interactions inside the body. A body force is a force density that acts on every material point inside the object, so when you sum (or integrate) over the volume you get the total force. Gravity is the classic example: every little volume element dV experiences a gravitational force rho g dV, and integrating over the entire volume gives the weight. This is different from surface forces, which act on the boundary surface (like pressure on the surface), or internal forces, which are forces between parts of the same body. External forces come from outside the object and can be either body or surface in nature, but the phrase “acts on the volume” uniquely identifies a body force.