Lift on an Immersed Body in a Fluid Stream

The correct answer is option 'D': Dynamic fluid force component exerted on the body perpendicular to the approach velocity.

Lift is a force that acts perpendicular to the direction of the fluid flow and is responsible for the upward motion or support of an immersed body in a fluid stream. It is commonly experienced in the context of aerodynamics, where it enables the flight of airplanes and other flying objects. However, lift can also be observed in various other situations involving fluid flow, such as the buoyancy of ships and submarines.

Explanation:

1. Buoyant forces:
- Buoyant forces are responsible for the support of an object immersed in a fluid, but they act in the vertical direction.
- These forces are exerted as a result of the difference in pressure between the top and bottom surfaces of the object.
- While buoyant forces contribute to the overall forces acting on an immersed body, they do not directly cause lift.

2. Resultant fluid force on the body:
- The resultant fluid force on the body is the vector sum of all the forces exerted by the fluid on the body.
- This resultant force includes both the drag force (parallel to the approach velocity) and the lift force (perpendicular to the approach velocity).
- The resultant fluid force determines the overall motion and behavior of the immersed body but does not exclusively cause lift.

3. Dynamic fluid force component exerted on the body parallel to the approach velocity:
- This component of the fluid force is referred to as drag force.
- It acts parallel to the approach velocity and is responsible for opposing the motion of the immersed body in the fluid stream.
- The drag force is not responsible for lift but rather affects the resistance and motion of the body.

4. Dynamic fluid force component exerted on the body perpendicular to the approach velocity:
- This component of the fluid force is referred to as lift force.
- It acts perpendicular to the approach velocity and is responsible for the upward motion or support of the immersed body.
- The lift force is directly responsible for causing lift on the immersed body and enables its motion in a fluid stream.

Therefore, the correct answer is option 'D': Dynamic fluid force component exerted on the body perpendicular to the approach velocity.