Question 3 A fast spinning tennis ball in the air of density 1.23 kg/m3 will result in its deviation from the vertical trajectory as a result of lift force. Table Q3 shows the average speed and tennis ball spin rate from top male tennis player. In a tennis tournament, a tennis ball of 65.4 mm diameter is used and being hit by one of your favourite tennis player.
(a) By potential flow theory, determine the stagnation points location on the tennis ball and sketch the flow field around the tennis ball.
(b) Determine the lift force experience by the tennis ball as in Q3(a).
(c) In a prestigious tennis tournament, a good strategy need to be taken by your favorite tennis player in order to give a difficult prediction of the tennis ball
trajectory to his opponent. Using your knowledge in potential flow theory, explain
how the strategy will influent the tennis ball trajectory.
(d) In another situation, a negative lift can be experienced by the tennis ball. Explain
briefly how this effect is possible with the stagnation points' location.
(e) In a wind tunnel experiment for drag and lift measurement on the tennis ball,
pressure tapping on the tennis ball surface will give the pressure distribution data. Derive the pressure distribution expression so that the experimental and theoretical data can be compared.

Table Q3 - Average speed and spin rate for some male tennis players (extracted from Alam and Subic, 2008)