View Full Version : Question about the Sweetspot

02-15-2009, 04:12 PM
You often hear about pro's hitting the sweetspot which is part of the reason why their shots are so much more consistant and powerful compared to us. I've been playing tennis for a while and I'd like to think that I am hitting the sweetspot but I'm not sure I am. I know it's not off center because my shots don't feel dead. However there are these rare times where the ball feels like nothing when I make contact and the ball comes off deep and powerful with no effort. Is that the real sweetspot? Is that how it feels for pros when they hit? Do they consistantly hit that magical spot that feels like you're hitting air? Please give me your insight/thoughts! Much appreciated!

02-15-2009, 04:15 PM
I think your hitting the Harmonic spot, or whatever its called, where there isnt any vibration in the racquet because the way the strings contact the ball, theres 3 sweet spots, one for power, one for vibration, and another for something else. Been a while since ive read about sweet spots sorry. :oops:

02-15-2009, 04:49 PM
Yes, I believe that there are 3 so-called "sweetspots". Actually for serves & overheads it is common to hit a bit higher in the stringbed than the sweetspot(s).

02-15-2009, 06:17 PM
Ah I see. So do pro hit the one that usually has no vibration or do they hit the one that we hit usually where it is solid?

02-15-2009, 06:20 PM
this concept of the 3 sweetspots, are there any diagrams of this? This sparks my interest quite a bit.

02-16-2009, 03:52 AM
You may be sorry that you asked since it is not really a simple matter. In fact, the experts don't completely agree on the details. For the most part, 3 theoretical sweet spots have been identified for tennis racquets, baseball & cricket bats, swords, etc. Note that all 3 sweet spots are independent of each other and are usually located in different areas.

One of the so-called sweet spots is the COP = center of percussion (http://en.wikipedia.org/wiki/Center_of_percussion). The COP is that spot (or area) on the stringbed that produces little to no shock in your arm or hand on impact with the ball. It is generally located somewhere near the center of the stringbed, on the center axis of the racquet.

Note, however, the least shock doesn't necessarily mean the minimum vibration. Minimal vibration occurs at the (vibration) node of the first harmonic (aka, the node of the fundamental vibrational mode). When a ball hits the node, you don't feel any vibration in your hand. When it hits the COP, your hand doesn't feel any force pushing against it.

wiki.answers.com/Q/What_is_the_sweet_spot (http://wiki.answers.com/Q/What_is_the_sweet_spot_on_a_baseball_bat)

A racquet or a bat that has struck a ball will vibrate in a complex manner, much like a piano string that is struck when a key is depressed. Take a look at the following page to get an idea of the vibrational modes:

kettering.edu/~drussell/bats-new/bend-sweet.html (http://www.kettering.edu/%7Edrussell/bats-new/bend-sweet.html)

Note that one of the sweetspots (above) are not always the best places to contact the ball for maximum power transfer. For a volley, one of these sweetspots may be ideal. However for the serve (or overhead), a spot somewhat higher in the stringbed will produce a faster ball speed. The place where the ball will rebound with the greatest speed is the area with the highest coefficient of restitution.

Some sources also refer to a center of oscillation, the area on the string bed where the racquet's bounce is maximized. On the other hand, other sources indicate the center of oscillation and COP are equivalent.

illumin.usc.edu/article.php?articleID=152 (http://illumin.usc.edu/article.php?articleID=152)
What is the sweet spot on a tennis racquet? (http://tennis.about.com/od/tennisracquetsfaq/f/faqracquets46.htm)

Tennis Warehouse University articles:

twu.tennis-warehouse.com/learning_center/maxshotspeed.html (http://twu.tennis-warehouse.com/learning_center/maxshotspeed.html)
twu.tennis-warehouse.com/learning_center/PPandspeed.html (http://twu.tennis-warehouse.com/learning_center/PPandspeed.html)

Futher reading -- more about COP and sweetspots:

www.exploratorium.edu/baseball/sweetspot.html (http://www.exploratorium.edu/baseball/sweetspot.html)
www.kettering.edu/~drussell/bats-new/sweetspot.html (http://www.kettering.edu/%7Edrussell/bats-new/sweetspot.html)
www.kettering.edu/~drussell/bats-new/cop.html (http://www.kettering.edu/%7Edrussell/bats-new/cop.html)
Center of Percussion (Harvard) (http://www.fas.harvard.edu/%7Escdiroff/lds/NewtonianMechanics/CenterofPercussion/CenterofPercussion.html)

02-16-2009, 03:56 AM
This diagram is from one of the links above:

http://illumin.usc.edu/_images/pictures/i8_152_Tennis_fig01.jpg (http://illumin.usc.edu/article.php?articleID=152)

02-16-2009, 07:34 AM
thanks for the great info, SA. I really appreciate it :).

02-16-2009, 11:49 AM
That's rather interesting... It always felt strange that, when the sweetspot was supposed to be in the center of the racquet, why did I always tend to hit serves at the top of the stringbed, but yet it wouldn't behave like a mishit?

So it turns out that the sweetspot isn't dead center... there's more than one and each behaves differently... Thanks for the info SA :D

02-16-2009, 12:05 PM
Wow! Thanks for all the amazing info SA! So when it feels like a solid impact I'm hitting the node and when it feels like I'm hitting nothing I am hitting the COP?
Is there anyway to locate the COP and consistantly hit it? Do you know if pros hit the COP or node?

02-17-2009, 01:42 AM
when hitting the sweet spot your shot will sounds more like a ploink sound :P like more metal sound instead of the pop. Basically it will sound clean

02-17-2009, 05:09 AM
Wow! Thanks for all the amazing info SA! So when it feels like a solid impact I'm hitting the node and when it feels like I'm hitting nothing I am hitting the COP?

This could very well be.

Is there anyway to locate the COP and consistantly hit it? Do you know if pros hit the COP or node?

The COP could vary somewhat -- it may depend, in part, on where you hold the racket. So the COP could very well be different for a 2-handed stroke than for a 1-handed stroke since the pivot point might be different. The mass of the hand/racket system might also be a factor since the 2nd hand would change this total mass.

Don't know for certain where the pros hit. It would depend on the type of shot they were hitting -- flat serve, spin serve, volley, or groundstroke. They could hit at/near the COP, the primary (fundamental) node, a 2nd harmonic node, or somwhere between these 2 nodes.

I would imagine that they almost always hit the ball somewhere or/near the center axis of the racket (stringbed). On a shot with heavy spin, the ball travels across the strings a bit -- so they may hit across one of the sweetspots in that case.

For more info about this subject, I'll have to borrow a copy of the book, Technical Tennis, by tennis physicist Rod Cross and racket/string expert, Crawford Lindsey. Does anyone have access to a copy of The Physics and Technology of Tennis (Brody, Cross, Lindsey)? In the meantime, take a look at a page for Rod Cross' (tennis physics) web site:

Physics.usyd.edu.au/~Cross/tennis.html (http://www.physics.usyd.edu.au/%7Ecross/tennis.html)