Question

In describing the size of a large ship, one uses such expressions as "it displaces 20,000 tons." What does this mean? Can the weight of the ship be obtained from this information?

Short answer

The ship weighs 20,000 tons as it displaces 20,000 tons of water, indicating its weight.

Step-by-step solution

Understanding 'Displacement'

The term 'displacement' in the context of a ship refers to the weight of the water that the ship displaces when it is floating. This is based on Archimedes' principle, which states that a body submerged in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the body.

Linking Displacement to Ship's Weight

According to Archimedes' principle, the weight of the ship is equal to the weight of the water it displaces. Therefore, if a ship displaces 20,000 tons of water, then the weight of the ship is 20,000 tons. This is because the ship must displace a volume of water that weighs exactly the same as the ship in order for it to float.

Confirming the Ship's Weight

Given that a ship displaces 20,000 tons of water, this indicates that the weight of the ship itself is 20,000 tons. The expression 'displaces 20,000 tons' directly refers to the weight of the ship.

Key concepts

Understanding Ship Displacement

Ship displacement is a critical concept in naval engineering, often used to express a ship's size and weight. When we say a ship "displaces 20,000 tons," we are pointing to the weight of the water pushed aside by the hull of the ship when it floats. According to Archimedes' Principle, this displacement provides a direct measure of the ship's weight.
The physics behind displacement involves observing the volume of water the ship occupies. This volume directly corresponds to the weight of the water displaced. Hence, if the displaced water weighs 20,000 tons, the ship also weighs 20,000 tons. This equivalence helps us understand the floating mechanics of ships and how they maintain buoyancy.

The Principle of Buoyancy

Buoyancy is a force that acts opposite to gravity, enabling objects to float or at least not sink with their full weight. This principle is key when understanding ship dynamics. A ship floats by displacing a volume of water whose weight equals its own.
The Archimedes' Principle explains buoyancy succinctly: any object submerged in a fluid experiences a buoyant force equal to the weight of the fluid it displaces. Therefore, even large ships remain afloat as long as they can displace enough water to counterbalance their weight. This balance between buoyant force and the weight of the ship is what keeps it stable, floating, and capable of carrying additional loads such as cargo and passengers.

• Buoyant force acts upward against gravity.
• It is equal to the fluid's weight displaced by the object.
• This principle applies to all fluids, including liquids and gases.

Fluid Mechanics and Ships

Fluid mechanics provides the foundation for understanding how fluids behave and interact with various structures, such as ship hulls. This field studies how forces in fluids, like water, affect objects within them, applying both to liquid and gaseous contexts.
In ship design, engineers use fluid mechanics to calculate essential parameters like drag, lift, and stability, ensuring that vessels can efficiently navigate through water.

• Calculating resistance: Ships must overcome water resistance, requiring precise hull design.
• Maintaining stability: Ensuring the ship displaces enough water to remain balanced.
• Enhancing efficiency: Minimizes drag and maximizes buoyant support.

By mastering fluid mechanics, engineers can design ships that are not only stable but also fuel-efficient, able to withstand varying sea conditions while maintaining safety.