Abstract:
A new golf tee that increases the distance obtained on a drive is described. The tee increases driving distance by minimizing the energy absorbed by the tee when it is struck by the golf club. By absorbing less energy from the club head, the new tee minimizes the amount club head speed is reduced at impact, which translates into increased driving distance. The new tee also aids the golfer by providing a structure that allows the golfer to easily and consistently determine the amount the tee has been inserted into the ground.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims benefit of Provisional application serial No. 60/213,923, filed on Jun. 26, 2000. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to a golf tee.  
         BACKGROUND OF THE INVENTION  
         [0003]    A traditional prior art golf tee is shown in FIG. 1. Golf tees are typically made from a single piece of wood. The geometry is easily formed using readily available machining equipment, such as high-speed lathes. Tee  100  in FIG. 1 has shaft  10  that is tapered to a point at end  20  to facilitate inserting end  20  into the ground. The top of shaft  10  is flared out to a larger diameter. Top  30  of tee  100  is formed into cupped surface on which a golf ball can comfortably rest. The purpose of a golf tee is to support a golf ball a short distance above the ground until contacted by the face of a golf club.  
           [0004]    There are numerous variations of golf tees that can be found in the prior art. Some of these purport to increase the distance obtained. Each of these prior art tees has numerous drawbacks that limit their usefulness. The current invention overcomes these limitations.  
           [0005]    Disco et al in U.S. Pat. Nos. 5,413,330 and 5,683,313, describes what is referred to as an improved hollow tee. The tee is marketed under the name “Velocitee”, and the marketing literature states that the tee, “Provides the golfer with an uphill lie situation. This can produce overspin which increases roll and distance.” 
           [0006]    These tees are designed to be manufactured using injection molding techniques. They cannot be economically manufactured using traditional wood turning methods. As a result, they are considerably more expensive than traditional wood tees. The tee of Disco has a large diameter hollow cylindrical shaft connected to a smaller diameter solid shaft with a point at one end for insertion into the ground. The hollow cylindrical shaft is sliced at an angle at the top where the golf ball rests. The tee is designed to be inserted at an angle into the ground, slanting towards the target, so that the top of the shaft (that was cut at an angle) rests parallel to the ground.  
           [0007]    Unfortunately, the tee cannot function to promote overspin as intended. The spin imparted to the ball has solely to do with the trajectory of the club head through impact. The tee does not alter this trajectory, and therefore cannot affect spin. It is also interesting to note that the body of the patent disclosure does not mention the production of overspin as an object of the invention, it is only mentioned in the marketing literature. The only real benefit to the design that is mentioned in the patent disclosure of Disco is the use of a vent, so that the hollow cylindrical shaft is not completely sealed when a golf ball is placed on the top of the shaft.  
           [0008]    The vent supposedly keeps a vacuum from developing as the golf ball first leaves the tee after being struck by the golf club. No evidence is provided that such a vacuum would occur without the vent, or that such a vacuum actually has an adverse impact on the ball flight. A statement is made that incorporation of the vent will allow more of the club momentum to be transferred to the ball (compared to use of a hollow shaft tee without such a vent), but no analysis is provided. It should be noted that traditional tees would not require such a vent, if the vacuum described by Disco were in fact real, as there is no enclosed air space underneath the ball when it is placed on top of a traditional tee. No direct claim is made in the patent disclosure of Disco that his design provides for increased driving distance compared to traditional tees.  
           [0009]    The design of Disco also introduces a number of problems. The method used to insert the tee into the ground is different from that used for traditional tees. The exact angle the tee is inserted needs to be correctly judged by the golfer or the top of the tee will not be parallel to the ground and the ball may not be stable when set in place. There is no mechanism provided for the golfer to determine what this angle is. The tee may need to be inserted into the ground numerous times until the correct angle is obtained. Second, the tee must be rotated to the correct point, or the surface where the ball is supposed to rest will be rotated away from being parallel to the ground. Third, the tee is visually quite different from existing tees. Any difference in what the golfer sees when standing over the ball, compared to what is seen using traditional tees, can cause a problem. Because of the size of the tee and the required insertion angle, the golfer can see part of the tee when standing over the ball. This is not desirable. Finally, there is no straightforward mechanism to adjust and/or gauge the height of the ball above the ground when using this tee. It is important for the golfer to be able to consistently insert the tee so that the ball is the desired height above the ground. This can&#39;t be accomplished using this tee. Furthermore, different golfers will want to tee the ball different heights above the ground. The fixed angle of the Disco tee does not allow the height to be altered easily.  
           [0010]    Another tee marketed under the name “BoomBoyz” by SPL International, Inc. purports to increase driving distance. These tees are made using wood turning techniques similar to existing prior art tees. These tees have a slightly different shaft geometry than prior art tees. One section of the tee shaft is made thicker than normal. The marketing literature states that the tee should first be inserted as far into the ground as possible. Then it is pulled back up to the desired height, and rocked forward in the hole formed when it is inserted into the ground. The intent is to have the tee in the ground, but not tightly held by the ground, so that it will provide less resistance when contacted by the club head. This design may be able to affect driving distance to a degree. If the tee is not held tightly in the ground, it will be more likely to come out of the ground when struck by the club head (as long as it does not break), and it will require less energy to accomplish this than if the tee were held tightly.  
           [0011]    Reducing the energy removed from the club head when it contacts the tee, as intended in this second prior art tee, is also fundamental to the functioning of the new tee described in following disclosure. However, the methods by which energy removed from the club head is reduced in the “BoomBoyz” tee and the tee of the current invention differ substantially.  
           [0012]    Reducing the energy removed from the club head by reducing the stability of the tee when placed in the ground, as implemented by the “BoomBoyz” tee, introduces a number of problems. First, when used as intended the top of this tee will not sit perpendicular to the ground, but will rest at an angle with respect to the ground. This makes it more difficult to balance the golf ball on the top of the tee. Second, the tee will not be held firmly in place in the ground. It is therefore possible for the tee to move after it has been inserted. This can change the desired ball position and/or ball height after the golfer has set the ball in place and is getting prepared to swing. Third, there is no mechanism provided that allows the golfer to gauge the height of the top of the tee above the ground after it has been inserted into the ground. Fourth, the “BoomBoyz” tee has a thicker shaft, which requires more force to insert into the ground than traditional tees do.  
           [0013]    Finally, holding the tee in the ground less firmly does not guarantee that less energy will be absorbed by the tee when it is impacted by the club head. It is still possible for the tee to be broken when struck by the club head. (Breaking the tee constitutes the worst-case situation of energy absorption from the club head.) In fact, because the shaft of the “BoomBoyz” tee has been made thicker, a much larger input of energy is required before it would actually break. If the “BoomBoyz” tee were firmly contacted by the club head, it is actually possible for it to absorb significantly more energy from the club head than would a traditional tee, depending on how it is contacted, how it is held in place, and the characteristics of the ground. The method of insertion described in the marketing literature is not sufficient to guarantee that the “BoomBoyz” tee would absorb less energy from the club head under all circumstances.  
           [0014]    The new invention described below provides a tee that increases driving distance while overcoming all of the drawbacks of the prior art tees. The new tee reduces the energy removed from the club head when it contacts the tee (which results in increased driving distance) by altering the characteristics of the tee. The new tees can be manufactured using existing turning (machining) techniques, and inherently provide a mechanism to gauge the height of the top of the tee above the ground. The new tees remain stable when inserted into the ground, and do not alter what is seen by the golfer when standing over the ball. The new tees require the same amount of force to insert into the ground as traditional wood tees.  
         OBJECTS OF THE INVENTION  
         [0015]    It is an object of the current invention to provide a golf tee that achieves an increase in driving distance compared to prior art tees.  
           [0016]    It is another object of this invention to provide a golf tee with a feature that allows a golfer to accurately and repeatably gauge the height of the top of the tee above the ground when the golfer inserts the tee into the ground.  
           [0017]    It is another object of this invention to provide a tee that increases driving distance while requiring the same force to insert into the ground as a conventional tee.  
           [0018]    It is another object of this invention to provide a tee that increases driving distance while maintaining the same stability when inserted into the ground as a conventional tee.  
           [0019]    It is another object of this invention to provide a tee that increases driving distance that can be manufactured using any conventional tee manufacturing process.  
           [0020]    It is another object of this invention to provide a tee with all the above benefits without increasing manufacturing cost compared to conventional tees.  
         SUMMARY OF THE INVENTION  
         [0021]    Driving distance is determined by how much momentum is transferred from the golf club head to the golf ball at impact. In order to maximize driving distance, this momentum transfer must be maximized. Significant research goes into the design of golf clubs to improve this transfer. Energy transfer from the golf club to any structure or medium other than the golf ball prior to the point the golf ball leaves the club face, does not contribute to the momentum of the golf ball. The tee is one such structure.  
           [0022]    It is common for a golfer to break the golf tee on a drive. Work is required in order to break (or permanently deform) the tee. The club head supplies the energy needed to accomplish this work. Even if the tee does not break, the tee will be displaced and the ground around the tee will be permanently deformed. Work will still be done on the tee and the ground. Again, the club head supplies the energy needed to perform the work done. In either case, the energy used to perform the work is removed from the club head.  
           [0023]    It has been determined that this energy is removed from the club head while it is still in contact with the golf ball. According to the USGA (United States Golf Association), the typical contact time (the amount of time the golf ball is in contact with the club head) on a normal drive is approximately 0.45 msec. The club head will travel a distance of 0.8″ during that time (for an assumed club head velocity of 100 mph). This distance is less than the distance between the bottom of the club head and the tee at the point of first impact of the ball with the club head. The exact distance between the bottom of the club head and the tee at the point of first impact depends on the degree of loft of the clubface and the height of the club head above the ground during the swing. This distance has been calculated to be approximately 0.5″ (assuming a driver with 10″ loft and a swing that brings the bottom of the club head 0.25″ below the top of the tee). Therefore, the club head will strike the tee before the golf ball leaves the face of the club. Furthermore, the club head will travel approx. 0.3″ after it contacts the tee. This is a sufficient distance to completely break the tee.  
           [0024]    The removal of energy from the club head when it contacts the tee reduces the club head velocity at the point of impact. The reduced velocity shows up as a loss of momentum of the club head. Therefore, there is less momentum available to be transferred to the golf ball. This in turn reduces the maximum initial velocity of the golf ball as it leaves the club head. It is this initial velocity, in conjunction with launch angle (which is a function of the club head design and its position through impact) that primarily determine the distance the golf ball flies.  
           [0025]    The energy transferred from the golf club to the tee is no longer available to act on the golf ball. The result is reduced driving distance. The solution is to provide a tee that can adequately perform the function of holding the golf ball a desired distance above the ground, while minimizing the energy transfer that occurs between the club head and the tee.  
           [0026]    A well-struck drive, with a club head speed of 100 mph (44.7 m/s) at the point of impact will fly approx. 275 yards. The typical driver has a club head mass of approx. 200 g (0.2 kg). The momentum of the club head is then 8.94 kgm/s (M=mv, where M is momentum of the club head, m is the mass of the club head, and v is swing velocity). Measurements have shown that the momentum absorbed by a typical wood tee when it breaks is on the order of 0.2-0.4 kg m/s. Virtually all of this momentum will be absorbed by the tee while the golf ball is still in contact with the club head. Therefore, the club head momentum will decrease by approx. 2.2-4.5% due to contact with the tee. This translates to a typical distance loss (due to energy transfer from the club head to the tee, and possibly the ground as well) of 6-12 yards (2.2-4.5% of 275 yards). Driving distance can therefore be increased by as much as 6-12 yards if the energy transferred to (or the momentum absorbed by) the tee and ground can be eliminated.  
           [0027]    The reduction in distance due to use of conventional tees remains approximately constant regardless of swing velocity. High handicap golfers with slower swing speeds will see approximately the same improvement in absolute driving distance as low handicap golfers with faster swing speeds. As swing speed decreases, club head momentum decreases. Therefore, the momentum transferred to the tee (which is approximately fixed) represents a larger percentage of the total club head momentum. However, the total momentum of the club head is smaller, because the swing velocity is lower. The momentum absorbed by the tee is a larger percentage of a smaller quantity. The net effect is that the actual effect on absolute driving distance remains approximately constant over a wide range of variation in swing velocity.  
           [0028]    Use of other types of tees designed for increased durability may in fact have a larger detrimental effect on driving distance. Some of these tees will not break when struck by the club head. When such a tee is used in a tee box with hard ground, significantly more energy may be removed from the club head in displacing the tee and deforming the ground. Increasing the durability of tees, of which there are many prior art examples (tees with larger than normal shaft diameters, tees made out of hard polymer materials, etc.), will adversely affect driving distance.  
           [0029]    The current invention minimizes the amount of energy removed from the golf club head when it contacts the tee during the swing by reducing the strength of the tee shaft (compared to traditional tees) to forces applied perpendicular to the shaft. In the preferred embodiments, the reduction in shaft strength is accomplished over a first section of the shaft. The remaining portion of the shaft is kept at the traditional tee shaft strength. It should be understood that the invention is not limited in any way to the strength of this remaining portion of the shaft. The reduction of shaft strength results in a tee that breaks with a much lower applied force than required by traditional tees. By reducing the strength of the tee shaft, the tee will break with less energy input from the club head. Therefore, more energy is available to be transferred to the golf ball, which will increase the distance the golf ball travels.  
           [0030]    The fundamental idea on which the invention is based is that the new tees are designed to break when used. That is, the new tees are designed to be single use. This is contrary to conventional thought with regard to tees, where if anything there has been a desire to make tees last longer by increasing their strength. The invention here realizes that if the cost of the tee can be kept small, the increased distance achieved will outweigh the increased costs associated with a single use tee (the tees themselves do not cost more, but more tees will be used per round of golf).  
           [0031]    The new tee design only reduces the strength of the tee over a section of the shaft length. The rest of the shaft has characteristics similar to traditional tees. This is done so that the new tee requires approximately the same force to insert into the ground as a traditional tee. Also, the stability of the new tees when inserted in the ground will be similar to traditional tees.  
           [0032]    The preferred embodiments reduce shaft strength over a section of shaft length by forming a feature that acts as a stress concentrator. The stress concentrator focuses energy input to the tee from the club head at the point of reduced shaft strength, rather than distributing the input energy along the entire shaft length as occurs in traditional tees. This acts to further reduce the perpendicular input force needed to break the tee, which in turn further reduces the energy (or momentum) absorbed by the tee. The stress concentrator is located at a point along the shaft where it will be approximately flush with the ground when the tee is inserted into the ground by the golfer. This forms a moment arm between the top of the tee (where the club is most likely to contact the tee due to its shape which flares at the top) and the location of the stress concentrator. This moment arm also acts to reduce the input force required to break the tee.  
           [0033]    The addition of a stress concentrator feature does not significantly impact the compression load the new tee can withstand. The new tee has the same resistance to breaking as a traditional tee when inserted into the ground by a golfer (force is applied parallel to the shaft axis), but it will break with significantly less energy input from the club head compared to a traditional tee when impacted perpendicularly by the club head.  
           [0034]    It should be noted that it is also possible to reduce the strength of a tee shaft over its entire length (which would typically be done by reducing the shaft diameter). This approach, however, has the drawback that the portion of the shaft inserted into the ground has now has a reduced diameter. The stability of a smaller diameter tee when inserted into the ground (especially if the ground is soft) will be significantly reduced. Such a tee could change position after being inserted in the ground, which would adversely affect the drive.  
           [0035]    The above design also does not have a stress concentrator feature, and will therefore still absorb more input energy before it breaks than will the preferred embodiment. The energy input from the club head will be distributed along the entire exposed shaft length, rather than being concentrated at a particular point along the shaft (as occurs in the preferred embodiment). For a fixed amount of input energy, the stress present at any point along the shaft of a reduced shaft diameter tee will be less than the stress present at the location of the stress concentrator in the preferred embodiment (for the case where the shaft diameter at the location of the stress concentrator is the same as the shaft diameter of the reduced diameter tee). It can be seen that it will take more energy to break a tee without a stress concentrator feature than it will take to break a tee with a stress concentrator feature, and that the use of a stress concentrator feature also allows the new tee to have improved in-ground stability.  
           [0036]    It should be noted that there is no restriction on the diameter of the tee shaft of the present invention. A stress concentrator feature can be added to a tee with any desired shaft diameter. The preferred embodiments keep the nominal shaft diameter approximately the same as that used in traditional prior art tees, but this is not required.  
           [0037]    There is another function of the portion of the shaft with reduced strength (or the stress concentrator feature). Having a stress concentrator feature provides a visual reference point for determining how far the tee has been inserted into the ground. A tee with reduced diameter over its entire shaft length does not provide such a reference point. This reference point can be used to judge the height of the top of the tee above the ground. Use of this reference allows the golfer to repeatably tee his ball a consistent height above the ground.  
           [0038]    Yet another benefit is related to reducing the energy absorbed by the tee. When the golf club head contacts the tee, it applies a force to the tee. At the same time, an equal and opposite force is applied to the club head by the tee. This force, in addition to reducing club head velocity, is also capable of altering the position of the club head through impact. Depending on the trajectory, the club head can be caused to rotate slightly in one or more axes when it contacts the tee. This occurs while the clubface is still in contact with the golf ball. The rotations applied to the club head can impart unwanted spins to the golf ball. These spins can potentially accentuate hooks or slices. By minimizing the force needed to break the tee, as is done in the current invention, the reaction forces exerted by the tee on the club head are also minimized. Any detrimental effects on club head trajectory due to contact with the tee will therefore also be minimized.  
           [0039]    Finally, it is possible to manufacture a tee with a stress concentrator feature (a tee with reduced strength over only a section of its shaft) using exactly the same processes used to manufacture conventional tees. No secondary operations are required, and no processing throughput time penalty or cost increases will be incurred. The feature can easily be made using the wood turning techniques currently used to make traditional tees. Turning methods could also be used to make tees out of other materials (such as extruded plastic rod), if desired. The new tees can also be made using molding techniques, where the stress concentrator feature is incorporated directly into the mold cavity used to form the tee. The features and benefits of the new tees (compared conventional tees) are provided without any cost penalty. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0040]    Other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiments and the accompanying drawings in which:  
         [0041]    [0041]FIG. 1 shows a two dimensional (2D) cross sectional view of a typical prior art golf tee.  
         [0042]    [0042]FIG. 2A shows a 2D cross sectional view of the preferred embodiment of the new distance enhancing golf tee with a notch in the shaft that acts as a stress concentrator and tee height indicator.  
         [0043]    [0043]FIG. 2B shows a 2D cross sectional view of the preferred embodiment of the new distance enhancing golf tee with a radiussed notch.  
         [0044]    [0044]FIG. 3 shows a 2D cross sectional view of an alternate embodiment of the new distance enhancing golf tee with two separate stress concentration regions.  
         [0045]    [0045]FIG. 4 shows a 2D cross sectional view of an alternate embodiment of the new distance enhancing golf tee.  
         [0046]    [0046]FIG. 5 shows a 2D cross sectional view of an alternate embodiment of the new distance enhancing golf tee. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0047]    A stress concentrator feature on the shaft of a golf tee can be defined as an area of the tee shaft where the shaft strength has a local minimum. That is, on either side of the location of the stress concentrator feature on the shaft, the strength of the shaft is greater than the strength of the shaft at the location of the stress concentrator feature.  
         [0048]    In the preferred embodiment, the shaft strength is reduced over a relatively small section of the shaft length. The most straightforward method to reduce shaft strength is to reduce the shaft diameter. The preferred embodiment has a small section of shaft with reduced diameter, which in effect forms a notch in the shaft. The notch acts as a stress concentrator, which focuses the energy input from the club head to the location of the stress concentrator feature.  
         [0049]    In order to act reasonably as a stress concentrator, the diameter (or thickness) of the tee shaft at the location of the local minimum should be at least 10% smaller than the nominal diameter of the shaft in the local region around the stress concentrator. The preferred embodiments have a local minimum in the shaft diameter that is 40% smaller than the nominal shaft diameter. However, it should be noted that there is no limitation on the required percentage difference in shaft diameter at the local minimum compared to the nominal shaft diameter. Different ratios may be desirable for different nominal tee shaft diameters or with tees made of different materials.  
         [0050]    Most of the discussion here focuses on tees made of wood, which are made on high-speed lathes. This manufacturing process results in tees that have a cylindrical geometry, and are circularly symmetric. The invention is not however limited to such geometries. A stress concentrator feature could be added to a tee with a shaft that had a square or rectangular cross section, for example. Such a tee could be made using a different manufacturing process, such as injection molding of a polymer material.  
         [0051]    A stress concentrator feature also does not need to extend around the entire perimeter of the tee shaft. An effective stress concentrator feature could exist on only one side of a tee shaft, or on opposite sides of the shaft (or extend over only a portion of the circumference of a round shaft). For example, a second operation could be added where a traditional tee is placed in a press to form notches on opposite sides of the tee shaft. Drilling a small hole, either partially or completely through the tee shaft, can also create a stress concentrator feature. Such a hole would weaken the shaft at the location of the hole.  
         [0052]    The invention is not limited in any way in the materials used to form the tee, the geometry of the tee shaft (cross section shape or thickness), or the geometry of the stress concentrator feature and the extent to which it extends around the perimeter of or through the tee shaft. All that is required is a feature that creates a local minimum in the strength of the tee shaft.  
         [0053]    A tee with a stress concentrator (formed by a notch) in the shaft is straightforward to manufacture. Since traditional wood tees are simple turnings, changing the diameter over a section of the shaft can be accomplished by changing the geometry of the tool used to make the turning. There is no increase in manufacturing time or cost required to accomplish this. No secondary operations are needed to form the stress concentrator in the shaft. A stress concentrator feature can also easily be incorporated in the tooling for a molded tee without affecting the cost of the part. No increase in material costs or machine cycle times would be needed. FIG. 2A shows a cross section of the preferred embodiment of the new tee design. Tee  200  is similar to prior art tee  100  shown in FIG. 1, except for stress concentrator  40  in shaft  1 . Holes or other geometries that can form stress concentrators can be accomplished without additional costs when certain manufacturing methods are used (holes can be done easily in injection molding, for example) or with slight cost increases using secondary operations (such as drilling a hole in a formed tee). Tee  500  in FIG. 5 shows hole  80  drilled through the shaft  10  of tee  500 , where hole  80  forms a local minimum in perpendicular shaft strength at the location of the hole.  
         [0054]    In use, the new golf tee  200  is inserted into the ground until the portion of shaft  10  with reduced strength (stress concentrator feature  40 ) is approximately flush with the ground. When the club head contacts the golf ball and tee  200 , shaft  10  of tee  200  will break at the location of stress concentrator feature  40 . Furthermore, by locating this point flush with the ground, the moment arm that is formed between the location where the club head impacts top  30  of tee  200  and the stress concentrator feature  40  maximizes the force applied at stress concentrator feature  40 , for a fixed energy input from the club head. When the club head applies a force to the top of tee  200  perpendicular to the axis of tee shaft  10 , tee shaft  10  will break with a much smaller applied force than would a traditional tee. The accompanying reduction in club head velocity that occurs when the tee  200  breaks will be significantly less than the reduction that occurs when a traditional tee is used.  
         [0055]    In order for tee  200  to function properly, the club head must contact tee  200  somewhere between the location of the stress concentrator  40  and the top of tee  30 . If the club head contacts tee  200  between the location of stress concentrator  40  and the ground, then tee  200  will break along shaft  10  below stress concentrator  40 , and the tee will absorb the same energy (or momentum) as a traditional tee. This is the reason why the preferred embodiment locates stress concentrator  40  a distance below the top of tee  30  so that stress concentrator  40  will be approximately flush with the ground when top of tee  30  is the desired height above the ground. Note that it is also possible to insert tee  200  farther into the ground (so that stress concentrator  40  is slightly below the surface of the ground) and still have it function correctly. The amount stress concentrator  40  can be pushed past the ground surface and still have the tee function correctly depends primarily on the characteristics of the ground. The softer the ground, the farther tee  200  can be inserted and still work effectively.  
         [0056]    Tee  200  retains sufficient strength to resist breaking when a force is applied to top  30  of tee  200 , parallel to the tee shaft  10  axis. This is required in order to be able to insert the tee into the ground. It has been determined that the diameter of traditional tees provides a column that can withstand much greater compression loading than is needed in order to insert a tee into the ground. Reducing the diameter of a portion of the shaft as required by the current invention can therefore be done while still maintaining sufficient strength to withstand the compression loads typically encountered.  
         [0057]    The preferred embodiment locally reduces the diameter of shaft  10  of tee  200  by approximately 40% to form the stress concentrator feature  40 . Shaft  10  of tee  200  in the preferred embodiment has a nominal diameter of 0.19″, and the diameter at the location of the stress concentrator feature  40  reduces to 0.11″. Note that the invention is not in any way limited to these dimensions. The invention only requires that there be a section of the shaft with a locally reduced strength compared to the rest of the shaft.  
         [0058]    Stress concentrator  40  in shaft  10  of FIG. 2A is shown with sharp corners. Sharp corners increase the stress concentration that occurs, by reducing the area over which the input force is distributed. It may be desirable to reduce the amount of stress concentration for a given shaft strength (a given diameter or thickness) to improve the manufacturing yields of the device. The radiuses of the edges of stress concentrator  40  determine the areas over which stress is concentrated. A very small radius results in very high levels of local stress, and could adversely impact manufacturability of the device. A slight increase in the radius can be used if desired to accomplish a reduction in stress concentration for a given reduction in shaft strength.  
         [0059]    Tee  201  is shown in FIG. 2B with a radiused stress concentrator. Joint  41  of stress concentrator  40  is the most critical to radius to reduce stress concentration if needed for manufacturability. The preferred embodiment uses a radius of 0.015″ for joint  41  of stress concentrator  40 . It should be noted that the invention is not limited to the use of any particular radius. The depth of the notch and the dimension of the radius in joint  41  can both be varied to achieve different mechanical characteristics. The invention is not limited in any way in the combination of shaft diameter and stress concentrator radius used.  
         [0060]    Stress concentrator  40  in shaft  10  (of tees  200  and  201 ) should be located a distance below top of tee  30  so that top of tee  30  is the desired height above the ground when the tee is inserted in the ground (to the point where stress concentrator  40  is approximately flush with the ground). The preferred embodiments locate stress concentrator  40  approximately 1.0″ below top  30 , which is a desirable distance for use with a typical driver. It should be understood however that the invention is not in any way limited to this dimension. In fact, the preferred distance between stress concentrator  40  and top  30  will be smaller for a tee shot with an iron club (or a fairway wood) than a tee shot with a driver. In the case of a tee shot with an iron club, stress concentrator  40  will preferably be located approximately 0.30″ below top of tee  30 . Again, it should be noted that the invention is not in any way limited to locating the stress concentrator at any of the above-identified distances away from the top of the tee. The use of distances other than those identified above will still result in a tee with reduced momentum absorption compared to traditional tees.  
         [0061]    It is also possible to construct a tee with more than one section of the shaft with reduced strength (or more than one stress concentrator feature). The invention is not limited in the number of stress concentrators contained in the shaft. An example embodiment is shown in FIG. 3, where tee  300  contains two stress concentrators in shaft  10 . Stress concentrator  40  in shaft  10  of tee  300  is located a distance from top  30  of tee  300  selected to be optimum when a driver is used for a tee shot, and stress concentrator  50  in shaft  10  of tee  300  is located a distance from top  30  of tee  300  selected to be optimum when an iron is used for a tee shot.  
         [0062]    Tee  400  in FIG. 4 shows another alternative embodiment of the new invention. The nominal diameter of shaft  10  on either side of stress concentrator feature  40  is no longer the same, as was shown in FIGS. 2A, 2B, and  3 . The nominal diameter of shaft section  70 , which is the section between top  30  and stress concentrator feature  40  of tee  400  is smaller than the nominal diameter of shaft section  60 , which is the section between tip  20  and stress concentrator feature  40  of tee  400 . There is still a local minimum shown in the shaft diameter that forms stress concentrator  40 .  
         [0063]    This alternative embodiment allows the stress concentrator feature to continue to function, regardless of the depth tee  400  is inserted into the ground. Tee  400  can now be inserted into the ground past the point where stress concentrator  40  would be flush with the surface of the ground, yet still function as intended. Only section  60  of tee shaft  10  will be held in place by the ground. Since section  60  has a larger diameter than section  70 , section  70  will not be held firmly in place by the ground, even if tee  400  is inserted so that stress concentrator  40  is located a significant distance below the ground surface. Input force will still be concentrated at stress concentrator  40 , and the tee will still break at this point. This design can effectively be used for a driver or an iron shot without the need for multiple tees with different distances between the top of the tee and the location of the stress concentrator, or tees with multiple stress concentrators. This design does not require the tee to be fully inserted, pulled out to a desired height and then rocked forward as required by one prior art tee. Tee  400  will be held firmly in place in the ground while still providing its driving distance improvement.  
         [0064]    The preferred embodiment shown in FIG. 4 uses a diameter for shaft section  60  of 0.20″, a diameter of 0.15″ for section  70 , and a diameter at joint  41  of stress concentrator  40  of 0.1″. Stress concentrator  40  is located 1.0″ from the top of the tee (the same as the distance identified earlier for tees  200  and  201 , for use with a driver). It should be noted that this embodiment is not limited in any way in the diameters (or thickness) used for the various shaft sections, or in the location of stress concentrator  40 . The dimensions given here are representative, and have been shown to work well. They are not the only dimensions that will work, and the invention should not be construed to be in any way limited to use of only these dimensions. The key elements of this embodiment are: 1) use of a stress concentrator feature located at a point along the shaft of a tee, and 2) a first section of the tee shaft below the stress concentrator feature that has a first diameter or thickness, a second section of the tee shaft above the location of the stress concentration feature that has a second diameter or thickness, where the diameter or thickness of this second section of tee shaft is less than (or equal to, as described in previous embodiments) the diameter or thickness of the first section of tee shaft.  
         [0065]    Other embodiments will occur to those skilled in the art and are within the following claims:  
         [0066]    What is claimed is: