Final answer:
The buoyant force is the vertical force that acts upward, opposing the weight of an immersed object in a fluid.
Step-by-step explanation:
The vertical force that always acts upward and is responsible for the buoyancy of objects in a fluid is the buoyant force. It occurs because the pressure at the bottom of an object submerged in a fluid is greater than the pressure at the top, creating a net upward force. This force can allow objects to float, sink, or remain suspended in a fluid, depending on whether the buoyant force is greater than, less than, or equal to the weight of the object. The buoyant force is an upward force exerted by a fluid that opposes the weight of an immersed object. It is responsible for objects floating in fluids, such as boats floating on water.