When the boat pulls the water tube behind it, the boat exerts a force on the tube, causing it to move forward. This force propels the tube in the direction of the boat's motion. Once the boat stops applying force (i.e., when it stops pulling the tube), the only force acting on the tube will be the drag force of the water acting against the tube's motion.
As a result, the net force acting on the tube is now the drag force, which acts in the opposite direction of its motion. This net force slows the tube down due to deceleration caused by the friction between the tube and the water. The tube will continue to slow down until it eventually comes to a stop, assuming no other forces act on it (like the boat moving again or an external push).
In summary, the dynamics are as follows:
- When the boat pulls the tube: The boat applies a forward force, causing the tube to accelerate.
- When the boat stops pulling: The force from the boat is removed, and the only horizontal force left is the drag force, which acts in the opposite direction.
- Resulting motion: The tube slows down due to the net force being negative (in the direction opposite to its initial movement).
This scenario is a great illustration of Newton's first law of motion, which states that an object in motion will remain in motion at a constant velocity unless acted upon by a net external force.