A small card is placed on top of a spool as shown in Fig. P3.121. It is

Question:

A small card is placed on top of a spool as shown in Fig. P3.121. It is not possible to blow the card off the spool by blowing air through the hole in the center of the spool. The harder one blows, the harder the card "sticks" to the spool. In fact by blowing hard enough it is possible to keep the card against the spool with the spool turned upside down. Give this experiment a try. It may be necessary to use a thumb tack to prevent the card from sliding from the spool. Explain this phenomenon.

Figure P3.121