Because motion or change (kinêsis) is mentioned in the definition of nature, any discussion of nature will need to rely upon the explanation of motion. One might—erroneously—thinkthat this is an easy task, because Aristotle's categories (as listed in the Categories and also elsewhere) do contain two related types of entities, action and passion. Aristotle's discussion of motion in the Physics, however, starts out in a somewhat different manner. When he submits that there is no motion besides the categories (Physics 3.1, at 200b32–201a3), he does not assign motions to the categories of action and passion. After mentioning that the entities in the categories come in oppositions, Aristotle submits a few lines later (at 201a8–9) that there are as many kinds of motion and change as there are kinds of being. This means that motions are grouped here with the entities of the category where they effect change.
Within the four domains where genuine change can occur, change alwaysrequires the existence of a potentiality which can be actualised. Butchange is neither identical to this potentiality, nor to the lack of aproperty, nor, without further qualifications, to the actuality whichis acquired when the potentiality is actualised (Physics 3.2,201b33–35). It is a special kind of actuality, the actuality of thepotential in so far as it is potential (Physics 3.2,201a27–29). Aristotle's formulation strongly suggests that the potentiality actualised in the process of change is not a separate and independent potentiality for motion, alongside the entity's potentiality for harbouring the end-state of the process: the process, say, house-building, and the end result, the house, are different actualisations of the same potentiality of a set of materials that is buildable into a house. Not only would Aristotle's definition beuninformative and circular otherwise, amounting to the tautologousclaim that change is the actualisation of the capacity for change, thefurther qualification in the definition, that change is the actualityof the potential in so far as it is potential, would be completelyidle. This further restriction is meant to select among the differenttypes of the realisations of the same potentialities. As Aristotle stresses these are the incomplete actualities belongingto these potentialities, because what is actualised in a process ofrealisation is an incomplete potentiality only (Physics 3.2,201b32–33). Accordingly, potentialities of change are readmitted intothe ontology. They, nevertheless, do not feature as potentialities intheir own right, but as the incomplete variants of the fundamentalpotentiality for an end result.
High school physics students study kinematics in depth, and in doing so require a system capable of recording and breaking down an object’s motion so that it can be studied using physical principles.
Since the end of the 17th century, the vast improvements in the technology and society have evolved the meaning of the word motion in terms of physics from ‘a simple movement’ to ‘a change in position, if acted upon by an unbalanced force’.
The definition of motion suggests that such processes can becharacterised in terms of a property or state of an entity, acquiredas a result at the end of the process, which can be labelled the form within this process, and an initial lack of thisform. Furthermore, Aristotle claims, there is a third component, whichis not changed in the process, the substrate or subject of the motion(Physics 1.7).
Even though the foregoing might have suggested that generation ofsubstances is fundamental for all the other kinds of changes, in factlocomotion will have a privileged status. All other changes depend onlocomotions, because any two entities involved in change, with theiractive and passive potentialities respectively, need to come intocontact in order for the interaction to occur. Contact, however, as a rule needs to be established by locomotion:either the entity to be moved, or the mover, or both, need to proceedso that they meet (Physics 8.7, 260a26-b7). Moreoverlocomotion is the form of change which can occur in isolation ofgeneration, perishing and the other forms of change (Physics8.7, 260b26–29). Other changes are indepedent kinds of change insofaras they can occur in an entity which does not perform any otherchange. Nevertheless all these forms of change include or presupposethat some other entity engages in locomotion.
Aristotle claims that in a chain of efficient causes, where the firstelement of the series acts through the intermediary of the otheritems, it is the first member in the causal chain, rather than theintermediaries, which is the moving cause (Physics 8.5,257a10–12). Then, both in cases of natural generation and artificialproduction, it is only this first efficient cause which has to satisfythe requirement of synonymous causation. Aristotle's prime example, that human generates human, is also such a case. Here, the causal efficacy of the paternal human form is transmitted through the generative potentialities of the semen of the father. The semen, however, although it acts as an efficient cause in the process of the formation of the embryo, is not a human; it does not possess the form it transmits in the same way as the male parent. Aristotle's discussion makes it clear that this is not an isolated instance of anexception from the general principle. He compares the case to theactivity of a craftsman, where the form of the product of the artisticproduction is in the soul of the craftsman, and then through themotions of the instruments this form can get imposed on the materialmanufactured into an artefact. The instruments and their motions areefficient causes of the process, but they do not contain the form inthe same way as the soul of the craftsman (On the generation ofanimals 730b14–23 and 740b25–29, for further discussion see theentry on ).
Third, the principle of causational synonymy is restricted tosubstances at the end of Metaphysics 7.9, and in the first half of the same chapter the non-standard presenceof some causally relevant forms may also be envisaged. Aristotle's example there is the heat in motion, which produces heat in the body when the doctor rubs the patient in the appropriate manner. This heat in the motion can be the presence of an active potentiality in the motion which is able to elicit heat in the body, without heat being predicable of motion itself. But even if such non-inherential subsistence of properties is not envisaged in this passage—thealternative being that the heat in motion is the heat in the skin ofthe patient, caused by the rub, which then enters into the innerrecesses of the body, becoming heat in the body—some similar sort of presence is required in two large classes of cases: naturalgenerations and artificial productions.
Aristotle argues at the opening of Physics bk. 8 that motionand change in the universe can have no beginning, because theoccurrence of change presupposes a previous process of change. Withthis argument Aristotle can establish an eternal chain of motions andrefute those who hold that there could have been a previous stationarystate of the universe. Such an eternal chain, Aristotle argues, needsto rely on a cause which guarantees its persistence: if each of theconstitutive processes in the causally connected web were of finiteduration, for every one of them it can be the case that it is notpresent in the world, indeed, at some later time it will not bepresent any longer. But then the whole causally connected series ofevents, Aristotle submits, would also be contingent. Hence Aristotle postulates that the processes of the universe dependon an eternal motion (or on several eternal motions), the eternalrevolution of the heavenly spheres, which in turn is dependent on oneor several unmoved movers (Physics 8.6, 258b26–259a9).
To better understand the physics of a goalie, you must understand how Newton’s Three Laws of Motion work; Inertia, force equals mass times acceleration, and equal and opposite forces, as well as another law torque and leverage.