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Propeller (aka Cruise Ship) Boat

In this situation, a propeller is used to move the boat in one direction. The boat is moving at a constant velocity, so there is no acceleration. We are also using an ideal situation where the boat is moving across a still lake with no waves.

Free Body Diagram

There is a buoyant force acting the in direction opposite the gravitational force. These two forces are equal and opposite because the boat is not accelerating in either of those directions. There is the F_thrust that is applied by the propeller, moving the boat in that direction. The drag force in this case is mostly applied by the water as it resists the movement of the boat. There is a negligible amount of drag from the air, so it has been left out of the diagram. The F_drag is opposing the F_thrust, so they are acting in opposite directions. They are also equal in magnitude because the boat is not accelerating. The net force is zero, indicating that the boat is moving at a constant velocity.

Energy Cubes

The video shows how the energy is transferred in this situation. The energy starts as chemical energy in the form of fuel. As this is burned and the propeller spins, the boat starts moving so the chemical energy becomes kinetic energy for the boat. Some energy is lost as thermal, though, and this is shown by the thermal energy that goes into the water near the propeller and into the air above the boat. The boat does not move up or down (change its height), which is indicated in the video because no gravitational energy is lost or gained by the boat (in fact, gravitational energy was left out of the video because it has no change).

Other Scenarios - Sailboat (  please click me!)