the present invention now will be described more fully hereinafter with reference to the accompanying drawings , in which a preferred embodiment of the invention is shown . this invention may , however , be embodied in many different forms and should not be construed as limited to the embodiment set forth herein ; rather , this embodiment is provided so that this disclosure will be thorough and complete , and will fully convey the scope of the invention to those skilled in the art . like numbers refer to like elements throughout . the inventors of the present invention have discovered that a golf ball comprising a hard hollow sphere increases the moment of inertia and reduces spin , thereby increasing distance . in addition , the golf ball of the present invention provides increased spin retention , i . e . “ bite ”. the golf ball therefore combines the favorable characteristics of existing two - piece and three - piece balls , i . e . distance and “ bite .” furthermore , the inventors have discovered that a hollow metal sphere has excellent rebound properties which , when incorporated into a golf ball , can improve its performance . referring now to fig1 and 2 , an improved golf ball according to one embodiment of the present invention is illustrated . the golf ball 11 includes a hard , hollow sphere 13 surrounded by a second layer 14 . the second layer is then surrounded by an outer cover 15 . the sphere 13 is preferably made of a hard material having a specific gravity ranging from about 2 . 5 to 20 and more preferably from about 4 to 11 , an outside diameter ranging from about 0 . 39 inches to 1 . 50 inches ( about 1 . 0 to 3 . 8 centimeters ), and a thickness of about 0 . 02 to 0 . 25 inches ( 0 . 05 to 0 . 64 centimeters ) and more preferably about 0 . 02 to 0 . 08 inches ( 0 . 05 to 0 . 20 centimeters ). the hard material comprising the sphere may be any metal such as titanium , a titanium alloy , or other metal alloy including stainless steel , or an intermetallic material such as titanium and aluminum . the metal may also be iron , carbon steel , nickel , molybdenum , aluminum , tungsten or alloys of steel , nickel , aluminum , molybdenum , or tungsten . the metal comprising the sphere may have a brinnell hardness of greater than 40 . alternatively , the hard material may be a plastic which does not appreciably deform under loads usually placed on a golf ball such as polypropylene in which case the specific gravity is about 1 . 0 . if plastic , the hollow sphere may have a thickness of about 0 . 05 to 0 . 5 inches ( 0 . 13 to 1 . 27 centimeters ). the plastic comprising the sphere may have a shore d hardness of greater than 60 . the metal or plastic is preferably solid but may also be perforated or porous . a ceramic , including silicon carbide may be used . the sphere improves the moment of inertia of the ball , thereby reducing spin , by moving the mass away from the center of the ball . the diameter , thickness , and specific gravity of the sphere will vary depending on specific design parameters , including spin rate , feel or rebound , and materials used in construction of the ball . the second layer 14 is preferably of a compressible , resilient material , including natural rubber or synthetic polymer compounds or a combination thereof which is typically used in the manufacture of golf balls . examples of such synthetic polymer compounds are polybutadiene , which has a specific gravity of about 1 . 15 , polyisoprene , and styrene - butadiene . crosslinking or co - crosslinking agents may be added to the rubber comprising the second layer to control its hardness and thus deformation and elastic recovery properties as is well - known in the art . high gravity fillers as are also well known in the art may also be added to the rubber compound comprising the second layer . by using hollow sphere 13 to increase the moment of inertia , however , fillers can be minimized or eliminated from the second layer 14 altogether thereby allowing the use of softer rubber compounds in the second layer to improve rebound characteristics . the second layer 14 may be wound or molded construction . the second layer generally has an outside diameter of about 1 . 52 to 1 . 56 inches ( 3 . 86 to 3 . 96 centimeters ) and a thickness of 0 . 05 to 0 . 65 inches ( 0 . 13 to 1 . 65 centimeters ) and more preferably about 0 . 21 to 0 . 55 inches ( 0 . 53 to 1 . 4 centimeters ). the outer cover 15 may be an ionomer , urethane , balata , or synthetic elastomer . the outer cover also includes a dimple pattern as is well - known in the art . yet another embodiment of the improved golf ball 11 according to one embodiment of the present invention is illustrated in fig3 . the golf ball 11 includes a hard sphere 13 , as described above , surrounded by an outer cover 15 without a intermediate second layer . the sphere is preferably a metal , and more preferably titanium or stainless steel . this embodiment provides the greatest moment of inertia , less spin , greater rebound and , therefore , greater distance . in a preferred embodiment of the invention as shown in fig2 , the hollow sphere 13 is not filled with any solid or liquid material . thus , the hollow sphere contains a residual gas 12 , preferably air . the hollow sphere may also contain pressurized gas . preferably , the gas fills or substantially fills the hollow sphere . in another embodiment as shown in fig4 , the hollow sphere may contain a solid or liquid - based material 12 a . preferably , any solid or liquid material which may be placed inside the sphere is of lower density than the material comprising the second layer or outer cover surrounding the sphere in order to increase the moment of inertia of the ball . suitable solid materials may include natural rubber or synthetic polymer , cork , or plastics . suitable liquid materials include water and oil . vegetable or mineral oils may be used . if a solid material is used , the solid material may be comprised of layers of different materials . the outer cover 15 may be an ionomer , urethane , balata , or synthetic elastomer . the outer cover also includes a dimple pattern as is well known in the art . preferably , the golf ball 11 of the present invention has a minimum diameter of 1 . 68 inches , a maximum weight of 1 . 620 ounces , and a maximum initial ball velocity of 255 feet per second as measured on a standard u . s . g . a . ball testing machine . the golf ball 11 may be made using conventional processes and techniques as are presently employed in the art such as molding so that the ball will be spherical in shape , have equal aerodynamic properties , and have equal moments of inertia about any axis through its center . if plastic , the hollow sphere 13 , may be made by techniques , such as blow molding , which are well - known in the art . if metal , the hollow sphere 13 may be manufactured by forming two halves of a sphere by hot forming or cold forming which are then joined together by welding or other means sufficient to securely join the halves of the sphere together . methods of forming two halves of a metal sphere include stamping , hydroforming , metal spinning , and superplastic forming as are well - known in the art . methods of securely joining two halves of a metal sphere include welding ( such as electron beam welding , laser welding , and electrical resistance welding ) or metal gluing as are well - known in the art . metal spheres suitable for use according to the present invention can be obtained from industrial tectonics , located in dexter , mich . the outer layer and , if desired , the second layer are molded around the sphere using techniques that are well - known in the art . alternatively , the second layer , or any additional layers , may be wound as is well - known in the art . examples of golf balls made according to the present invention are shown below : two piece ball — titanium core and surlyn ( manufactured by dupont and registered tradename ) cover according to the following specifications : a hollow sphere comprising a titanium shell with an inside diameter of 1 . 374 inches ( 3 . 490 centimeters ), outside diameter of 1 . 521 inches ( 3 . 863 centimeters ), and a mass of 1 . 258 ounces ( 35 . 69 grams ). surlyn cover with a density of 58 . 68 lb / ft . sup . 3 ( 0 . 95 grams / cm3 ), an inside diameter of 1 . 521 inches ( 3 . 863 centimeters ), an outside diameter of 1 . 680 inches ( 4 . 267 centimeters ) and a mass of 0 . 3514 ounces ( 9 . 962 grams ). the residual gas in the core does not contribute significantly to the mass of the ball . the total mass of the ball is 1 . 610 ounces ( 45 . 65 grams ). the moment of inertia of the ball of example 1 is about 34 percent greater than a typical two - piece ball . three piece ball — titanium core , second layer of polybutadiene , and a surlyn cover : a hollow sphere comprising a titanium shell with an inside diameter of 0 . 992 inches ( 2 . 52 centimeters ) and an outside diameter of 1 . 102 inches ( 2 . 80 centimeters ), a specific gravity of 4 . 5 and a mass of 0 . 494 ounces ( 14 . 0 grams ). polybutadiene ( specific gravity = 1 . 15 ) with a layer thickness of 0 . 210 inches ( 0 . 53 centimeters ) and a mass of 0 . 762 ounces ( 21 . 61 grams ). surlyn ( specific gravity = 0 . 95 ) cover of thickness 0 . 0787 inches ( 0 . 2 centimeters ), and a mass of 0 . 348 ounces ( 9 . 87 grams ). the residual gas inside the core does not contribute significantly to the mass of the ball . the total mass of the ball is 1 . 604 ounces ( 45 . 5 grams ). the moment of inertia of the ball of example 2 is about six percent greater than a typical two - piece ball . as described above , the improved golf ball of the present invention provides improved performance characteristics including low spin rate , long distance , and bite without adversely affecting rebound characteristics . the ball of the present invention minimizes hook and slice when improperly hit . the design of the golf ball allows variations in the material and the size of the sphere , second layer , and outer cover in order to optimize performance characteristics . in the drawings and specification there has been set forth preferred embodiments of the invention and although specific terms are employed , the terms are used in a generic and descriptive sense only and not for the purpose of limiting the scope of the invention being set forth in the following claims .
a golf ball is provided that has a hard sphere core or layer that exhibits a controlled vibrational response . the vibrational response may be controlled by tailoring the stiffness or damping of the sphere with at least one element , such as a groove or any other type of indentation in the hard sphere core . the groove serves to locally reduce the wall thickness of the hollow metal sphere core , thereby reducing the stiffness of the core by allowing larger deformations under a load without significantly reducing the total mass of the core . this results in a golf ball that is legal for play and capable of drive distances essentially equivalent to those of currently available high performance golf balls , but that also maintains a high moment of inertia , allowing less hooks and slices during play .