Figure 103: Flow over an aerofoil
Figure 104: Ball suspended in upward air jet
Example 24 Stability of table-tennis ball suspended on air jet. The air speed v1 > v2 so p1 < p2 producing a resultant force pushing the ball towards the centre of the air jet (see …g 104). Example 25 De‡ection of a spinning rough ball. Ball moving at speed v through the air and spinning about a vertical axis as in …g 105. As ball is rough it slows down air at A and tend to increase speed of air at B, such that v1 < v2 , so that p1 > p2 producing a resultant force in direction from A to B. The ball is de‡ected horizontally. Note the ball is rough, a smooth ball does not drag the air round with it and the e¤ect is not observed.
81