The discussion revolves around two statements related to wave behavior in different water depths. The first statement involves a ship encountering waves that change in wavelength and direction as it approaches deeper water. The second statement describes an observer seeing a piece of wood moving against the current in a river where waves are moving in the same direction as the wind.
The discussion is ongoing, with participants sharing their interpretations and critiques of both the statements and the book's answers. Some have offered alternative explanations and expressed concerns about the clarity of the questions, while others are seeking validation for their reasoning.
Participants note that the questions may not effectively teach the underlying physics concepts and that the wording could lead to confusion regarding the physical principles being assessed.
haruspex said:Surface waves in a liquid are somewhere between the two. The molecules undergo a circular motion. Consider a cork floating on the water as a wave passes through. Start with the cork in a trough. At this point the cork is in its lowest position and moving in the opposite direction to the wave. Next, it rises on the leading edge of the next wave. Half way up, it is moving vertically. At the crest, it is moving with the wave, but at a lower speed, so the wave passes under it. Half way down, it is moving vertically again.
Viewed from the side, with the waves going left to right, the cork executes roughly a circle, clockwise.
Tom.G said:Barclay.
1) Consider a rope, maybe fifteen feet long. Tie one end of it to a doorknob or other fixed object. Take ahold of the free end and walk away until the rope is freely suspended in the air but not pulled tight. Now shake your end of the rope up and down. You will see a wave travel from your hand to the tied-off end of the rope. If the rope was traveling along with the wave it would be yanked out of your hand. The up and down DISTURBANCE of the rope is what we call a wave. This disturbance travels along the rope, but the rope itself doesn't rush to the doorknob. This is roughly what the wind does to water to make waves.
2) Now consider doing the above experiment in a train car. The rope is tied at one end of the car and you are standing in the aisle holding the other end of the rope. Repeat Step 1), above. You will get the same result. Even if the train is moving, you will get the same result. The moving train is the water current in the river..