Upthrust
Explanation
When an object is placed in a fluid (liquid or gas), it experiences forces due to the pressure exerted by the fluid. The pressure in a fluid increases with depth, leading to a net upward force on any immersed object. This phenomenon is central to the study of hydrostatics and is often discussed in the context of gravitation and Archimedes' principle.
Analysis of Options:
- Drag: Incorrect. Drag is the aerodynamic or hydrodynamic resistance force acting opposite to the relative motion of any object moving with respect to a surrounding fluid. It depends on the velocity of the object.
- Upthrust: Correct. Upthrust, also known as buoyant force, is the upward force exerted by a fluid on an object immersed in it. It counteracts the weight of the object and is caused by the pressure difference between the upper and lower surfaces of the object.
- Tension: Incorrect. Tension is the pulling force transmitted axially through a string, rope, cable, or chain. It is a force exerted by solid connectors, not fluids.
- Friction: Incorrect. Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. While fluid friction (viscosity) exists, the static upward force is specifically termed upthrust.
Key Takeaway:
Upthrust (or Buoyancy) is the net upward force exerted by a fluid on an immersed object, arising because fluid pressure increases with depth.