Final answer:
A laden oil tanker sits lower in the water compared to when it is empty because the total mass of the tanker and its cargo must be supported by the water it displaces. The displacement of water must be equal to the weight of the tanker for it to float, which means it sits lower when loaded due to the increased mass.
Step-by-step explanation:
The question touches on the principles of physics, specifically buoyancy and the displacement of water by a ship, which relates to a ship's draft. A laden oil tanker sits lower in the water when it is fully loaded with oil even though oil is less dense than water. This is because it is the total mass of the tanker that must be supported by the displacement of water.
When the tanker is empty, it displaces less water because the tanker itself has less mass. However, when it is loaded with oil, the combined mass of the tanker and the oil is greater, causing more water to be displaced and the tanker to sit lower in the water.
Let's consider the thermal expansion of materials too. While the density of oil is lower than that of water, the entire mass of the loaded tanker has to be accounted for. If this mass includes a substantial cargo of oil, the overall mass is significantly increased, requiring more water displacement for buoyancy.
Furthermore, issues such as the thermal expansion of materials play a role because both the steel of the tanker and the oil can expand, thereby affecting their densities. This is particularly significant in large volumes, such as those carried by tankers.
The buoyant force on a tanker, or any other ship, corresponds with the weight of the fluid it displaces. In the case of an oil tanker, when loaded, the increased weight requires displacing more water to achieve buoyancy, meaning the ship draws more water and sits lower in the water compared to when it is empty.