I could be wrong, but my impression of my serves is as listed below - can someone with a Physics background let me know if this is really what is haopening?
- Topspin serve jumps up in height the most and keeps getting higher for several feet. So a returner standing close will return at a lower height than a returner at or just behind the baseline. - the peak height might be near the baseline. But if the returner stands well behind the baseline, the ball stops rising and starts dropping so that they can make contact at a lower height than if they were close to the baseline.
- Flat serve height seems to depend on speed with faster flat serves staying lower. If I hit one of my fastest serves with good depth, it doesn’t come up at all and the returner has to make low contact whether he is close or at the baseline with the height dropping only slightly between those two spots - it drops further if the returner is well behind the baseline. This is what I thought the OP was describing. On the other hand, if the flat serve is slower, it actually seems to rise up more than the faster serve initially, but drops in height from its peak more by the time it gets to the baseline.
- Slice serve initially jumps up, but doesn’t have much forward momentum and so it starts dropping very quickly compared to all other serves. So a returner doing SABR returns close to the service line might make high contact, but anyone standing at the baseline or behind will experience an abrupt dropping of height from the peak and a low contact point. Slower slice seems to stay lower than faster slice maybe because the forward momentum decreases even more abruptly for the slower slice.
Is this accurate or does my visual experience not match the physics? I am just talking about height and not any sidespin as you can impart more or less sidespin to any slice, topslice or kick serve and it will impact the rate of drop in height of the serve. But let’s assume there is little sidespin for this question. - tough to hit slice without significant sidespin though. All my serves are hit with a continental grip including the flatter serves.