In professional tennis, why do they change new balls after 7 games and follow by 9 games?

Question

Is it because of at the start of the match, the balls have been played as a warm-up? Is there any rationale behind for practicing this?

Answer 1

Yes, it is because of the first set of balls having been used in the warm-up that they use them for fewer games. The rationale behind changes after 9 games is that the felt tends to wear & after several games the balls will get to be much like those that we who don't punish the ball as much have used for a couple of sets (i.e., not like new).

Answer 2

New Tennis Balls

Answer 3

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