A small piece of (3 times 5) card can be held onto a spool of thread by

Question:

A small piece of $3 \times 5$ card can be held onto a spool of thread by blowing air through the hole in the center as shown in Figure P11.15. The harder one blows, the tighter the card hangs on. Explain why this is so. You need to put a nail or thumb tack through the card's center to make sure the card does not slide off the spool.

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