Spin for flat hits

#1
Hi,

I understand that when brushing a ball, a topspin,slice, or side spin is generated. However, I have recently read that when a ball is hit directly flat (includes both flat severs, and groundstrokes), there will also be spin generated, which doesn't seem intuitive. Would anyone be able to explain the physics behind this.

Thanks.
 

time_fly

Professional
#2
It’s almost impossible to hit the ball in the dead center of the racquet at a perfectly opposing direction to the direction of flight of the ball, which is what you would need to have no spin at all (assuming the ball has no spin already, another big supposition). So most “flat” shots do have some spin on them, just not enough to substantially change the behavior of the ball during flight or on the bounce.
 
#3
Thanks for the explanation. After further thought, the racket will also create an inherent spin with the rotational directional motion of the racket. Yes. in a sense, every ball will have at least some spin.
 
#4
Forehands and backhands can be hit without any spin. With that being said, you will rarely see a pro hit even a flat shot without any spin. For a top spin or flat shot, we usually have to get our racket below the ball in order to get the ball over the net. If we do so even slightly, we’ll likely create some top spin even if our mind is screaming flat. Low to high swing usually creates some top spin. Your mind might be saying I want to hit flat, but that’s not what’s really happening. With that being said, I’ve seen many shots amongst recreational players sail over the net without any spin, so it’s possible.

When it comes to the serve, it’s also possible to hit a flat serve over the net without any spin. The kicker is whether or not one is hitting a flat serve with the correct continental grip. Flat serves with a continental grip have a swing path that is actually hit “upward” and therefore top spin is created even on serves that appear to look flat. This is why Sampras had thousands of RPMs even on his flat serve.
 

FiReFTW

Hall of Fame
#5
Modern ATP forehand with lag and snap and supination and pronation creates massive spin even when the trajectory is fairly flat, because the arm supinates and then pronates as the lag is released and the racquet is thrown into the ball, which makes the racquet tip go from bellow the ball upward extremely fast.

For reference, heresa slow motion:


You can see in most of these swings he barely gets bellow the ball at all, the swingpath is quite through the ball and fairly flat, but the supination and pronation of the forearm that lags the racquet and then snaps it, makes the racquet tip go bellow the ball and then pronate upwards as its released, and you can see even these flat trajectory shots have alot of spin on the ball.
 
#6
Modern ATP forehand with lag and snap and supination and pronation creates massive spin even when the trajectory is fairly flat, because the arm supinates and then pronates as the lag is released and the racquet is thrown into the ball, which makes the racquet tip go from bellow the ball upward extremely fast.

Great Point.

Unless there is a pushing motion rather than a rotational motion, a spin will be a created.


In respect to a flat serve, would the ball have underspin or topspin using this same explanation.
 
#7
For topspin, you must overcome the spin of the (topspin) ball bouncing towards you. If you don't have a steep enough swing angle or high enough racket head speed, you may produce a ball with little topspin, or even a little underspin(slice)...and if you get it just right(wrong?) you may produce a ball with almost no spin at all.
 
#8
IMNSHO the definition of a 'flat' ball is a ball with virtually no spin. Say, less than 5 revolutions before the ball bounces. It doesn't mean that the trajectory of the ball is flat, or straight, rather than curved.
 
#9
Because spin really has nothing to do with brushing the ball, it has to do with hitting the ball off-centre. i.e. racquet face angle RELATIVE to swing path is the important factor.
 
#10
In addition to the above explanations, please note that a ball with 0 spin once it touches the ground will create spin from the friction of the ground. So your receiving ball already have spin on it and so as long as you dont counter than spin, that spin will still be on the ball you return. And once your return stroke touches the ground it may have a different spin. Practically tennis ball will always have some spin, because of this.

when a ball is hit directly flat (includes both flat severs, and groundstrokes), there will also be spin generated
 
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