The present invention provides a ball for practising a sport or game particularly although not exclusively, the sport of golf, especially for practising putting.

In any sport or game involving a ball, the way in which the ball is struck is important for controlling the subsequent trajectory of the ball, whether it is struck with a hand, foot, racket, bat, club or whatever. This is especially so in golf where accuracy is very important, both in driving and putting.

For the most part, a golfer intends the ball to go straight and in putting this means to roll in a straight line along the surface of the green. Golfers practice putting strokes often and this can be done not only on a golf range but also in the home or office. The aim is to develop "muscle memory" so that the correct putting action becomes automatic.

The applicants have realised that if a ball could be devised which amplifies errors, ie. such that a small error in club action produces a pronounced deviation in the course of the ball, then it would be extremely useful in training to improve accuracy. Conversely, if such a hypothetical error amplifying ball were hit and yet rolled straight, it would mean that the stroke must be very good indeed.

US-A-4 603 861 describes a bowling ball having a homogeneous spherical core surrounded by lubricant to create a gyroscopic action to increase the number of pins knocked down. However, this ball is not capable of amplifying player errors.

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US-A-3 517 933 describes a ball for playing simulated lawn bowls. This ball has a loose-fit weighted core surrounded by fluid to simulate the braking effect of bowling green turf. Whilst this could amplify player errors, that is not the intended purpose and the sensitivity of amplification would be very poor.

GB-A-2 232 895 A describes a golf ball having a threaded member movable within the ball to move the centre of gravity to simulate play on a sloping surface. However, this intended purpose is not the same as deliberate amplification of player errors and although it might conceivably be just capable of fulfilling this purpose, again the efficiency of error amplification would be very low. Moreover, it has to be placed carefully in the correct orientation before play. US-A-3 655 197 describes an amusement ball for randomly indicating letter/numbers on an outer shell by means of an index mark on an inner ball. The inner ball may be partially surrounded by fluid. The inner ball is also provided with a counterweight to keep the index mark uppermost when the ball is at rest. However, this ball is not intended as a ball for practising or playing a ball game or sport. Even if the general form of construction of the amusement ball were to be transferred to such a sport ball, which in any case would never be considered by persons skilled in the relevant art, performance in error amplification would be mediocre.

A ball which is capable of behaving in such a way has now been devised and is, in accordance with the present invention, a ball for practising a sport or game, the ball comprising a shell containing inertia means for amplifying or exaggerating the effect of an impact or stroke to the ball.

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A further ^' aspect of the present invention provides a ball configured for practising a sport or game, the ball comprising a shell containing inertia means for amplifying or exaggerating the effect of an impact or stroke to the ball, wherein said inertia means comprises a generally spherical core freely rotatable within the shell arranged with a relatively close fit between the core and shell and with a layer of fluid therebetween.

Whilst not wishing to be bound by any particular theory, in deriving the concept which gave rise to the present invention, the applicants arrived at the following hypotheses: -

1. The best path is for the ball to roll in the direction in which it is struck. That is, it should be made to roll or spin on an axis perpendicular to the target line.

2. It is best if all imparted momentum is angular, with very little or no linear momentum.

3. A pure rolling motion will be least complicated in its interaction with the ground.

4. A golf professional's invariable advice to "follow through" is probably intended to induce the player to strike the ball in such a way that it will naturally roll.

5. A golfer wishing to improve his putting would be able to use a practice ball with the required characteristics to develop his swing to achieve the correct stroke.

Preferably, the inertia means comprises a fluid and at

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least one ^" solid member movable within the shell. More particularly, the inertia means may comprise a plurality of non-interacting fluids, or a mixture of fluids and a solid member or solid members movable within the shell. In this context, the term ' non-interacting' includes ' immiscible' . In a first preferred general alternative, the at least one solid member comprises a core freely rotatable within the shell. The total mass may be distributed between the shell and the core, according to the desired effect upon one or more predetermined aspects of dynamic behaviour of the ball.

Preferably, the core has a total mass greater than that of the shell. Provided that it is freely rotatable within the shell, the core may be of any suitable shape but it is preferred for the core to be in a form of a closed and/or solid inner ball. It is advantageous for such an inner ball to be a generally close fit inside the shell, separated from the inner wall of the shell by a layer of the fluid. Although not absolutely necessary, normally no fluid will be inside the inner ball.

According to a preferred embodiment, the core has a spindle inner part, preferably extending axially through the centre of the core. If the spindle part is weighted at one end, eg. by having a thickened portion, it will ensure that the spindle part always is restored to the upright position when the ball is at rest and preferably, this will occur within 10 seconds of the ball coming to rest.

At least part of the core (eg the spindle part) of various balls may respectively be made of different materials/have different densities or overall weights to modify the performance of each ball as will be described

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in more detail hereinbelow. Different such balls may be offered for sale alone or together as a set.

In a second preferred general alternative, the at least one solid member comprises at least one solid item "loose" within the shell but preferably a plurality of such loose solid items are provided. Typical examples are powders, eg. sand, or fine solids, metal shot, ball bearings or a mixture of any of these.

Whatever the form of the ball according to the invention, usually the fluid will be in the form of a liquid, preferably more viscous than water. An example of a suitable viscous liquid is hydraulic fluid although oil, glycerine, or even a gel or any other suitable liquid can easily be envisaged as an alternative. It is preferred for the liquid density to be as close as possible to the average core density. The otherwise free space within the shell may be wholly or partially filled with the fluid. Generally speaking, substantial complete filling is preferred for the first general alternative and partial filing for the second.

The ball may be in any shape or size and may for example have the shape and dimensions of a regular sport ball. However, in a preferred embodiment, it is shaped and dimensioned to resemble a golf ball. Thus reference to a ' stroke' refers to any impact appropriate for the ball in question, eg. being struck with an appropriate club, bat, racket, hand, foot or the like.

The shell may be formed wholly or partially of a transparent material with information such as an advertising logo marked on the shell to be visible through the transparent material. If the core is weighted so as always to come to rest with the same

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surface uppermost, then conveniently the information can be marked on this upper surface to be readily visible.

It is possible for the shell to be composed of two concentric parts. The inner part may comprise two interfitting portions (eg. hemispheres) which may co-operate (eg. by "snap" fit) to constitute the whole inner part. This facilitates manufacture, in particular filling the shell with the at least one solid member and fluid. The outer part is conveniently moulded around the inner part. This outer part may have the outward appearance of a particular kind of ball, for example a golf ball.

In an alternative embodiment, the golf ball may comprise an inner ball suspended by a liquid within an outer shell. A generally annular member, preferably in the form of ring shaped weight, is positioned in the equatorial region of the inner ball and a bias weight is located at a pole of the inner ball such that when the ball is at rest, the bias weight is lowermost and the ring shaped weight is disposed horizontally.

The present invention will now be explained in more detail by way of the following description of a preferred embodiment and with reference to the accompanying drawings, in which: -

Figure 1 is a cross sectional view through a first embodiment of a practice golf ball in accordance with the present invention;

Figure 2 is a cross sectional view through a second embodiment of a practice golf ball in accordance with the present invention;

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Figures 3A-3C show a cross-sectional view through a third embodiment of a practice golf ball according to the present invention and the effect of rolling on the contents thereof;

Figures 4A-4C show a cross sectional view through the ball shown in Figures 3A-3C, illustrating the effect of spin on the contents thereof;

Figure 5 is a cross-sectional view through a fourth embodiment of a practice golf ball in accordance with the present invention; and

Figure 6 illustrates possible trajectories which the golf ball of Figure 5 might take for various impact modes.

As shown in Figure 1, a practice golf ball 1 comprises a closed outer shell 3 which has a dimpled outer surface 5 to resemble a regular golf ball.

Inside the shell is placed a core in the form of a closed inner ball 7 which has an outer diameter just smaller than the inner diameter of the shell. The space between the inner ball and the shell is filled with hydraulic fluid 9.

A spindle core 11, made of a material having a higher density than the rest of the inner ball, runs axially through the centre of the inner ball. The spindle is substantially cylindrical and has a substantially a uniform diameter along the majority of its length. Clearly through, other shapes of spindle would be possible. At one end 13, the spindle has a portion 15 of increased diameter to act as a weight.

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The ball is of the same size and weight as a regular golf ball but the shell is sufficiently heavy to take up the required angular momentum.

The spindle is weighted at one end so that in use, the heavy end tends to sink to the bottom and the spindle will always to sink to the bottom and the spindle will always end up vertically aligned for the next stroke.

The viscous liquid (hydraulic fluid) acts as a damper; when the ball spins quickly the drag tends to bring the core along with the shell. The liquid surface will exert increased drag at higher velocities. When the ball comes to a halt, the weighted spindle rights itself within in a few seconds. This uprighting motion is smooth and relatively quick because of the drag exerted on the inner ball core, there being little relative velocity at this time.

If the ball is struck in any way off centre or with a side spin component through a "bad" stroke such as a "pull" or a "slice", the ball will wobble rather inelegantly telling the player he is not playing the ball correctly.

A badly struck ball will also tend to drag the centre core along but not along the line of spindle axis. In this way the device will spin out of balance and progressively more so as it rolls along.

The ball can be constructed with different materials and/or different dimensions for the spindle. This enables the "sharpness" of the ball to be varied. For example if the spindle is made of lead the diameter of the core is then smaller for the same total weight. The spindle mass will be concentrated near the vertical

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axis. This increases the tendency for the ball to roll erratically if hit badly and thus makes more difficult to hit an accurate shot.

By the same token, a lower density core material such as steel or aluminium will make the weight of the core the more evenly distributed. This will decrease the tendency for the ball to roll erratically in the event of a bad shot.

Thus, balls of various "sharpness" can be produced with different core materials, corresponding to various degrees of difficulty. Thus a set of balls could be sold together so that a player may progress in degree of difficulty as he or she improves in skill. It is even possible for the ball to be made with a two part shell which can be opened to change the core for one of a different type. However, this is less preferred as the need to refill with the viscous liquid would make the task both difficult and messy.

Referring now to Figure 2, there is shown a second embodiment which is a variant of the ball shown in Figure 1. Where the same reference numerals are used, these denote the same constituent features as shown in Figure 1.

In this second embodiment, the shell 3 comprises two concentric parts, namely an outer part 17 and an inner part 19. The inner part comprises two hemispherical portions 21, 23 which are joined by a snap-fit arrangement (not shown) at their junction 25.

The inner part 19 has a very smooth inner surface. Since the outer surface of the core 9 is also very smooth, there is very little friction between the two

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during us e.

For ease of manufacture, the core is encapsulated in the inner part 19 submerged in a body of the fluid 9. The resultant sub-assembly is then placed in a moulding machine and the outer part 17 is then moulded over the inner part, to have the dimpled outer surface 5 resembling a conventional golf ball. However, it would also be possible to form the shell as a complete sealed unit around the core, submerged in the fluid without use of this two-part encapsulation.

Referring now to Figures 3A-3C a third embodiment is shown. This is a variation of the embodiments of Figures 1 and 2, wherein the core is replaced by a plurality of fine solid spheres 27 and liquid 29 partially occupying the interior of the ball when at rest. At rest on the ground 31, the contents of the ball will settle to the bottom of the shell 3 thus aligning itself for the strike (Fig. 3A).

When struck with a normal impact by a putter 33 through the centre line, the contents 27, 29 of the shell 3 will first slosh against the inside of the shell in the direction of impact (arrows 35, 37) and will travel the first few inches together with the ball which will slide on its bottom along the floor (Fig. 3B). Fictional forces will slow the ball down and the sliding will give way to rolling as denoted by arrows 39, 31 in Fig. 3C. At this time the contents will roll with the interior surface of the hollow shell forming a circular ring 41 on a horizontal axis perpendicular to the direction of motion.

The advantageous effects of this third embodiment will now be explained with reference to Figures 4A-4C.

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If the ball is struck with a little side spin about the vertical axis, the contents will register this side spin (arrow 43) and cause the "ring" 41 to be inclined in the direction of the side spin 43. Subsequently, this will bias the motion of the ball at the point when sliding (denoted by arrow 45 in Fig. 4A) will progress to rolling (arrow 47 in Fig. 4B). This will "amplify" the side spin by rolling towards the direction of the incline. The resultant incline of the ring is denoted by axis 49 in Fig. 4C.

Figure 5 illustrates a fourth embodiment of practice golf ball having an inner ball 50 suspended inside an outer shell 51 by a liquid 53. The density of the liquid relative to that of the inner ball 50 is preferably such that the inner ball can freely move within the outer shell 51.

The inner ball 50 is hollow and provided with a weighted member 54 in its equatorial region and a bias weight 55 on one side or at a pole of the inner ball 50. The weighted member 54 is in the form of an annular ring, and the spacing between the sides 56, 57 of the ring determines the inertial characteristics of the golf ball. This outer surface has generally spherical curvature with a radius corresponding to that of the inner ball as a whole.

When the golf ball of Figure 5 is at rest, the bias weight 55 will cause the inner ball 50 to orientate so that the bias weight 55 is positioned at the bottom of the ball with the weighted member horizontal.

The dynamics of the golf ball of Figure 5 will now be described with reference to the trajectories illustrated

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in Figure ^' 6. When the outer shell 51 is struck precisely (i.e. accurately or "squarely") with the intention that it enters a target hole 58, the equatorial member 54 flips along in the direction of the strike. The bias weight 55 describes a circular path in the vertical plane in the direction of the strike thereby following the path indicated by the arrow A.

In the event that the golf ball is struck off-square, say in a downward direction, a spin component may be imparted to the ball. This will pull the bias weight out of the vertical plane and cause the bias weight 55' to deviate from rotation in a vertical plane. As a result, the golf ball 51 will describe an arcuate trajectory as illustrated by arrows B (ball struck with the club face open) and C (ball struck with the club face closed); the equatorial member 54 tending to roll on its edge with the bias weight 55 continuously pulling to one side.

Other possible trajectories are illustrated in Figure 6. In the event that the club face strikes the ball squarely but pushes the ball on impact, the likely trajectory is as indicated by arrow D. If the club face strikes the ball squarely but pulls on the ball on impact, the likely trajectory is indicated by arrow E in Figure 6.

In the light of this disclosure, modifications of the described embodiment as well as other embodiments, all within the scope of the appended claims will now become apparent to persons skilled in the art.

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