Why does a fireperson sometimes struggle when holding the pipe issuing water?
A fireperson struggles due to Newton's third law, which applies to all forces. When the pipe issues water, it exerts a forward force on the water. Consequently, the water exerts a backward force on the pipe with equal magnitude.
Similar to how water pushes a canoe's paddle forward, this reaction force acts on the pipe. Since the forward and backward forces act on different objects (the water and the pipe), they do not cancel each other. This backward reaction creates an unbalanced force on the pipe, forcing the fireperson to struggle to hold it steady.
Explanation
The textbook context explains Newton's third law using the example of a canoeist pushing water backwards, causing the water to push the paddle forward with an equal force. Applying this same principle to the fireperson's pipe: the pipe pushes the water forward, so the water pushes the pipe backward. Because these action-reaction forces act on different objects, they don't cancel out, resulting in an unbalanced backward force on the pipe that the fireperson must counteract, causing the struggle.