"I'm glad that you understand that," Robin's mother replied with pride. "As the helicopter flies through the air, the sound it makes moves in waves through the air. Most of the sound waves caused by the helicopter move out in front of the helicopter. We fly the airplane in front of the helicopter so the microphones record the loudest sound made by the helicopter," Jackie finished her explanation. "That explains why helicopters are even louder when they are landing," Robin said as she put her hands over her ears. They laughed together as they approached the computer lab.