The small black dots represent some of the individual molecules of air inside the tube.
On average, this is the motion of all the molecules in the tube. Imagine taking a snapshot of these dots so that you can see what they are doing at an instant in time. Use a single arrow for each dot to show which direction each would be moving at that instant.
Hints:
- What do the molecules near the nodes do?
- If the molecule at one antinode moves right, which direction should the molecule at the next antinode move?
📘 Detailed Explanation:
In a standing sound wave inside a tube, there are specific points where the behavior of air molecules differs:
➤ At a node, the displacement of air molecules is always zero. That means the molecules located here are not moving at all at that instant. Hence, we draw either no arrow or an arrow of zero length to represent this.
➤ At an antinode, the displacement is at its maximum. Air molecules here are moving the fastest. For instance, if the molecule at one antinode is moving to the right (→), then the molecule at the next antinode (which is half a wavelength away) will move to the left (←). This is because adjacent antinodes are 180° out of phase.
➤ For molecules between a node and an antinode, the motion transitions gradually. The arrows would gradually increase in length from zero (at the node) to maximum (at the antinode). However, the key focus is on nodes (no motion) and antinodes (maximum motion with alternating directions).
🧠 Summary:
- Molecules at nodes = zero velocity → no arrow
- Molecules at antinodes = maximum velocity → alternating directions
- Between nodes and antinodes = gradual change in velocity
🌀 Visualization:
Imagine this snapshot:
Tube: Boundary | N | A(→) | N | A(←) | N | A(→) | N | Boundary
(N = Node, A = Antinode, Arrows = Motion Direction)
✅ Final Understanding:
This representation helps visualize how air molecules behave in a standing wave pattern inside an open tube. Remember, it’s a snapshot at a particular instant — over time, these directions alternate due to the oscillatory nature of the wave.