Which description best explains how a propeller moves a boat?

Which description best explains how a propeller moves a boat?

• A. It generates lift perpendicular to the hull to raise the bow.
• B. It operates by rotating and drawing water from forward and around its blades, and forcing the water into a stream away from the stern, creating a dynamic pressure which moves the boat.
• C. It spins in place creating a water bubble to buoy the boat.
• D. It relies on hull drag to push water backward for propulsion.

Answer: (B)

A propeller moves a boat by accelerating water backward, and the boat is pushed forward in response. As the propeller blades rotate, they draw water from in front and around the blades and force it rearward, creating a stream that exits behind the stern. This backward acceleration of water produces thrust due to Newton’s third law: the action of pushing water backward creates an opposite reaction that moves the boat forward. The description captures this process by noting the rotation, the movement of water away from the stern, and the resulting dynamic pressure that propels the vessel. The other ideas—lifting the bow, relying on hull drag, or creating a bubble—don’t describe how a propeller actually generates forward propulsion.

A propeller moves a boat by accelerating water backward, and the boat is pushed forward in response. As the propeller blades rotate, they draw water from in front and around the blades and force it rearward, creating a stream that exits behind the stern. This backward acceleration of water produces thrust due to Newton’s third law: the action of pushing water backward creates an opposite reaction that moves the boat forward. The description captures this process by noting the rotation, the movement of water away from the stern, and the resulting dynamic pressure that propels the vessel. The other ideas—lifting the bow, relying on hull drag, or creating a bubble—don’t describe how a propeller actually generates forward propulsion.