Henry and Caleb experiment with how feathers and fabric behave differently in a wind tube made from a fan and a Plexiglas silo.Caleb (darker hair) first moves the feather into the wind flow and immediately releases it. He may sense that not only does the wind move the feather upward, it also pulls the feather from his hand. However, Caleb cannot see the pulling, only the rapid rise of the feather. Watch how Caleb shifts from releasing the feather immediately to holding it a moment to watch the air bend it upward (01:08). The feather bends upward but does not rise into the air column. The bending allows the boy to see the pulling force of the wind. Before he could only see the lifting force of the wind. He has invented a strategy that allows him to see a force that is otherwise not “readable.”Note that if the wind source were intermittent rather than continuous Caleb would not be able to test his prediction as effectively. Later, Henry invents a strategy to diminish the force of the wind. When a piece of plaid fabric remains floating beyond reach inside the tunnel, Henry places his palm over the face of the fan (01:48). The gap between the Plexiglas and the fan encourages Henry to manipulate the airflow as a means of retrieving the fabric.