You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND 
     Shock absorbers are used in downhole applications to protect equipment in the well if a tool string is accidentally dropped. The kinetic energy of a falling string or other object is dissipated by a shock absorber to reduce or eliminate damage from the impact. The shock absorber typically reduces the impact on the equipment by dissipating energy of the impact in a crushable member. Such shock absorbers may simply distribute the loads of impact over a longer time period without reducing the total load borne by the downhole equipment. In view of the different applications and conditions found in various wellbores, prior art shock absorbing configurations are not always effective. Additional systems and methods that reduce the total load borne by the downhole equipment would be well received in the art. 
     BRIEF DESCRIPTION 
     Disclosed herein is a downhole decelerating system. The system includes, a downhole tubular, a decelerator assembly movably engaged within the downhole tubular, a mandrel longitudinally movably disposed at the decelerator assembly, and at least one element disposed at the decelerator assembly in operable communication with the mandrel such that longitudinal movement of the mandrel causes controlled radial movement of the at least one element to interact with the downhole tubular to decelerate the decelerator assembly in relation to the downhole tubular. 
     Further disclosed herein is a method of decelerating a tool dropped within a downhole tubular. The method includes, contacting a downhole structure with a mandrel of a decelerator assembly in operable communication with the dropped tool, longitudinally moving the mandrel relative to a body of the decelerator assembly in response to the contacting, definitively radially moving at least one element disposed at the body in response to the longitudinally moving, and deceleratingly engaging the downhole tubular with the definitively radially moving of the at least one element. 
     Further disclosed herein is a downhole decelerating device. The device includes, a body movably engagable within a downhole tubular, a mandrel longitudinally movably disposed at the body, and at least one deceleration element disposed at the body in operable communication with the mandrel such that longitudinal movement of the mandrel with respect to the body causes controlled radial movement of the at least one deceleration element to decelerate the decelerating device in relation to the downhole tubular. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
         FIG. 1  depicts a cross sectional view of a decelerating system disclosed herein prior to impact; 
         FIG. 2  depicts a cross sectional view of the decelerating system of  FIG. 1  shown at an initial point of impact; 
         FIG. 3  depicts a cross sectional view of the decelerating system of  FIG. 1  shown with dogs radially engaged with a recess of the downhole tubular; 
         FIG. 4  depicts a cross sectional view of the decelerating system of  FIG. 1  shown after motion of a decelerator assembly ceased with respect to the downhole tubular; and 
         FIG. 5  depicts a cross sectional view of a decelerating device disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. 
     Referring to  FIG. 1 , a decelerating system  10  disclosed herein is illustrated. The system  10  includes, a downhole tubular  14  with a downhole structure  18 , depicted herein as a ball valve, positioned therein, and a decelerator assembly  22 . In addition to the body  26 , the decelerator assembly  22  includes, a mandrel  30  and at least one radially movable element  34  also referred to herein as a dog. A biasing member such as a tension spring (not shown) biases the dog(s)  34  radially inwardly toward the mandrel  30 , which extends longitudinally beyond the dog(s)  34  in both directions. The mandrel  30  is longitudinally movable relative to the body  26 , and the dog(s)  34 , and has a distal end  38  that extends well beyond the body  26 , in a downhole direction as illustrated herein. A tapered portion  42  of the mandrel  30  connects a first dimensioned portion  46  to a second dimensioned portion  48  of the mandrel  30 . The first dimensioned portion  46  is radially smaller than the second dimensioned portion  48 . Movement, therefore, of the mandrel  30  in an uphole direction relative to the dog(s)  34 , and body  26 , causes the dog(s)  34  to move radially outwardly as the dog(s)  34  ramps along the increasing radial dimension of the tapered portion  42 . 
     Referring to  FIGS. 2 and 3 , a decelerator assembly  22  falls in a downhole direction within the tubular  14  until the distal end  38  of the mandrel  30  contacts the downhole structure  18 , at which point the mandrel  30  ceases motion in relation to the tubular  14 . Continued downward movement of the rest of the decelerator assembly  22  causes relative longitudinal motion between the body  26  and the mandrel  30 . This relative motion causes the dog(s)  34  to ride along the tapered portion  42  of the mandrel  30  from the first dimensioned portion  46  toward the second dimensioned portion  48 . In so doing the dog(s)  34  moves radially outwardly through windows  54  in the body  26  as the dog(s)  34  ramps along the tapered portion  42 , as best seen in  FIG. 3 . As the dog(s)  34  travels radially outwardly it enters a recess  56  in an inner wall  52  of the downhole tubular  14 . 
     Referring to  FIG. 4 , downward velocity of the decelerator assembly  22  is decelerated until stopped by contact of the dog(s)  34  with an end  60  of the recess  56 . Cessation of movement of the dog(s)  34  causes cessation of movement of the body  26  since the dog(s)  34  is engaged through the windows  54  in the body  26 . 
     Through the foregoing structure, the decelerating system  10  is configured so that only the impact load of the mandrel  30  and deceleration thereof is bore by the downhole structure  18 . The rest of the loads due to impact and deceleration of the decelerator assembly  22  are bore by the tubular  14  through contact between the dog(s)  34  and the end  60  of the recess  56 . Damage to the downhole structure  18  can, therefore, be reduced or eliminated in comparison to the damage that could result if the full impact and deceleration loads of the dropped tool were permitted to be bore by the downhole structure  18  alone. 
     Referring to  FIG. 5 , an embodiment of a decelerating device  110  is illustrated with similar features to those illustrated in the decelerating system  10  above being designated with the same reference characters. Since the device  110  is similar to the decelerating assembly  22  only the primary difference of the device  110  will be detailed hereinbelow. The device  110  includes an inner wall  152  but does not include a recess  56  in the inner wall  152 . In the device  110  the decelerator assembly  22  is decelerated and optionally stopped by engagement with the inner wall  152  directly. This engagement can take on different forms with a few alternatives being discussed herein. 
     In one embodiment at least one dog(s)  134  simply frictionally engages with the inner wall  152 . Such frictional engagement can be aided by fabricating the dog(s)  134  out of a material that has a high coefficient of friction with the material from which the inner wall  152  of the tubular  14  is made. Alternately, the dog(s)  134  may include a coating or a shoe (not shown) attached thereto made of a material having a high friction coefficient. 
     In yet another embodiment, the dog(s)  134  may be configured to block fluidic flow between the decelerator assembly  22  and the inner wall  152  thereby hydraulically trapping fluid between the dog(s)  34  and the downhole structure  18  and forming a hydraulic brake. Additionally, a combination of more than one of the embodiments disclosed herein can be used in unison to decelerate the decelerator assembly  22  as well as any tools attached thereto when dropped within the downhole tubular  14 . 
     Embodiments of the decelerating device  110  may be configured to decelerate and stop motion of the body  26  prior to impact between the body  26  and the downhole structure  18 . Alternately, the decelerating device  110  may allow such contact only after sufficient kinetic energy has been dissipated to prevent damage to the downhole structure  18 , the decelerator assembly  22 , or the tool connected thereto. 
     While the invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

Summary:
Disclosed herein is a decelerating device. The device includes, a body movably engagable within a tubular, a mandrel longitudinally movably disposed at the body, and at least one deceleration element disposed at the body in operable communication with the mandrel such that longitudinal movement of the mandrel with respect to the body causes controlled radial movement of the at least one deceleration element to decelerate the decelerating device in relation to the downhole tubular.