PADI Divemaster Certification Practice Exam

If an object is neutrally buoyant in seawater, what will happen to it in fresh water?

1. It will float

2. It will sink

3. It will remain neutrally buoyant

4. It will rise

The correct answer is: It will sink

When an object is neutrally buoyant in seawater, it means that its overall density is equal to that of the seawater, allowing it to neither sink nor rise; it simply suspends in the water column. Seawater has a higher density than fresh water because of the salts and other dissolved substances it contains. When this same object is then placed in fresh water, its density becomes less than that of the fresh water due to the reduced buoyancy. Since the object is neutrally buoyant in seawater, it implies that it has a specific density that matches that of seawater, but in the less dense fresh water, it will no longer have enough buoyant force to support its weight. As a result, the object will sink in fresh water because it is effectively heavier than the volume of fresh water it displaces. This illustrates the principle that buoyancy is dependent on the density of the fluid in which the object is submerged. Therefore, the correct outcome when a neutrally buoyant object transitions from seawater to fresh water is that it will sink.