Racket power
The power of today's tennis game is only partly generated by the athletes themselves. Much of it comes from their rackets. New designs mean players can hit the ball with more speed and accuracy than ever before.
It started in the 1970s when the traditional wooden frame was replaced with metal. Since then various materials have been used. Graphite has made the biggest impact. Most professional tennis players have at least some graphite fibres in their rackets. Now the graphite can be mixed with materials such as boron and titanium to produce even stronger, and lighter, rackets.
Big-heads showing off
Wooden rackets used to have smaller heads and shorter strings. This was because the frames weren't strong enough to keep longer strings in tension. New materials have given much more strength to the frame, without adding any weight.
A stronger frame can support longer strings.
Nearly every racket now has an oversize head, almost double the size of a wooden racket. Oversize heads have a larger 'sweet spot' (the area at the centre of the racket, where the frame is best balanced and the strings work in harmony). So when the ball is hit slightly off-centre it will still end up where it was intended.
Minimizing wobble
Large heads are also much more stable against twisting when a ball is not struck in the central area. The physical property of the rackets, which produces this stability, is called the 'polar moment of inertia'.
The larger this is the less the racket will twist during an off-centre shot. The moment of inertia is proportional to the weight of the racket and the width of the head squared. The new rackets suffer slightly by being lighter. But this is more than compensated for by the increased head size.
Super strings
The job of strings is to absorb much of the incoming ball's energy and then return a fraction of that energy back to the ball. Research has shown that looser strings yield more power. Tight strings give more control and accuracy.
Quick whipping swing
Pre-1970s, players needed a long stroke to get the heavy wooden rackets up to a good speed for hitting the ball. The gradual acceleration gave them more control so that they could hit the ball exactly on the sweet spot of the racket.
With lighter rackets and larger sweet spots, modern players are able to use a quick whipping swing. They are less likely to find the same spot on the racket every time. Fortunately, new rackets are much less sensitive to the exact location of the ball on the strings.
The future
Engineers are creating endless combinations of different materials and designs to further improve rackets. Some players are now using 'hammer head' rackets, where the tip weighs more than the handle.
Longer rackets are becoming popular and players are switching to 28" or 29" long frames compared to the standard 27" of a few years ago. More extreme ideas for hexagonal or triangular heads are also being developed. But they haven't caught on with professional players yet.
It's not only bigger rackets that are transforming modern tennis.
Source: http://www.bbc.co.uk/science/hottopics/tennis/rackets.shtml