question: Can anyone explain why motion occurs if the reaction is opposite and equal?
comment: > if the reaction is opposite and equal? Because it is upon different objects. If I push a box, the box pushes me just as hard. But me and the box are not the same mass, and so the result of the push is not equal.
passages: As described by the third of Newton's laws of motion of classical mechanics, all forces occur in pairs such that if one object exerts a force on another object, then the second object exerts an equal and opposite reaction force on the first. The third law is also more generally stated as: "To every action there is always opposed an equal reaction: or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts." The attribution of which of the two forces is the action and which is the reaction is arbitrary. Either of the two can be considered the action, while the other is its associated reaction.
   Section::::Examples.:'Equal and opposite'.
  
  One problem frequently observed by physics educators is that students tend to apply Newton's Third Law to pairs of 'equal and opposite' forces acting on the same object.
   If the object is supported so that it remains at rest, for instance by a cable from which it is hanging, or by a surface underneath, or by a liquid on which it is floating, there is also a support force in upward direction (tension force, normal force, buoyant force, respectively). This support force is an 'equal and opposite' force; we know this not because of Newton's Third Law, but because the object remains at rest, so that the forces must be balanced.
   However, it is still true that F = F and F = F, as this is required by Newton's Third Law.
  
  Section::::Examples.:Causal misinterpretation.
  
  The terms 'action' and 'reaction' have the misleading suggestion of causality, as if the 'action' is the cause and 'reaction' is the effect. It is therefore easy to think of the second force as being there because of the first, and even happening some time after the first. This is incorrect; the forces are perfectly simultaneous, and are there for the same reason.
   When the forces are caused by a person's volition (e.g. a soccer player kicks a ball), this volitional cause often leads to an asymmetric interpretation, where the force by the player on the ball is considered the 'action' and the force by the ball on the player, the 'reaction'. But physically, the situation is symmetric. The forces on ball and player are both explained by their nearness, which results in a pair of contact forces (ultimately due to electric repulsion). That this nearness is caused by a decision of the player has no bearing on the physical analysis. As far as the physics is concerned, the labels 'action' and 'reaction' can be flipped.
   Section::::Examples.
  
  Section::::Examples.:Interaction with ground.
  
  When something is exerting force on the ground, the ground will push back with equal force in the opposite direction. In certain fields of applied physics, such as biomechanics, this force by the ground is called 'ground reaction force'; the force by the object on the ground is viewed as the 'action'.
   The equilibrium concentration position of a reaction is said to lie "far to the right" if, at equilibrium, nearly all the reactants are consumed. Conversely the equilibrium position is said to be "far to the left" if hardly any product is formed from the reactants.
  
  Guldberg and Waage (1865), building on Berthollet's ideas, proposed the law of mass action:
  
  where A, B, S and T are active masses and "k" and "k" are rate constants. Since at equilibrium forward and backward rates are equal:
   The concept of chemical equilibrium was developed after Berthollet (1803) found that some chemical reactions are reversible. For any reaction mixture to exist at equilibrium, the rates of the forward and backward (reverse) reactions are equal. In the following chemical equation with arrows pointing both ways to indicate equilibrium, A and B are reactant chemical species, S and T are product species, and "α", "β", "σ", and "τ" are the stoichiometric coefficients of the respective reactants and products:
   is covered by considering the sum of all forces.
   Section::::Action in classical physics.:Action of a generalized coordinate.
  
  This is a single variable "J" in the action-angle coordinates, defined by integrating a single generalized momentum around a closed path in phase space, corresponding to rotating or oscillating motion:
   Likewise, the spinning wheels of a vehicle attempt to slide backward across the ground. If the ground is not too slippery, this results in a pair of friction forces: the 'action' by the wheel on the ground in backward direction, and the 'reaction' by the ground on the wheel in forward direction. This forward force propels the vehicle.
  
  Section::::Examples.:Gravitational forces.
   BULLET::::2. Symport: S (out) + [H or Na] (out) ⇌ S (in) + [H or Na] (in)
  
  BULLET::::3. Antiport: S (out) + S (in) ⇌ S (in) + S (out) (S may be H or a solute)
  
  Section::::Mechanism.:Substrate specificity.
   Whenever one body exerts a force on another, the latter simultaneously exerts an equal and opposite force on the first. In vector form, if formula_8 is the force of body 1 on body 2 and formula_9 that of body 2 on body 1, then
  
  This law is sometimes referred to as the "action-reaction law", with formula_11 called the "action" and formula_12 the "reaction".
   In this case, experiments have determined that this reaction takes place according to the rate law formula_1. This form suggests that the rate-determining step is a reaction between two molecules of NO. A possible mechanism for the overall reaction that explains the rate law is:
  
  Each step is called an elementary step, and each has its own rate law and molecularity. The elementary steps should add up to the original reaction. (Meaning, if we were to cancel out all the molecules that appear on both sides of the reaction, we would be left with the original reaction.)
   Physical science is concerned only with mechanics. Therefore, it can be said that, in a collision, action and reaction are always opposite and equal. Such actions and forces, though, are only mathematical hypotheses. We only really know that the striking body loses motion and the struck body gains motion. We do not know if the motion is communicated from one body to another or if the motion is destroyed in the striker and is created in the struck. In the true nature of things, all bodies are passive. The truly active cause of motion is metaphysical and not the concern of physical science.
   - The cell will then reverse.
  
  - It will then stop and rotate.
  
  - Now facing a new direction, the cell will move off in that direction.
  
  This process will continue until the cell is able to negotiate its way around the obstruction.
  
  Movement of Paramecium cells is caused by control of calcium ions inside the cell and membrane potentials. The simplest explanation for the avoidance reaction is that membrane potential controls the influx of calcium ions, which regulates the beat frequency and angles of cilia on the surface of the cell.
   Section::::History.:1864.:The equilibrium state (composition).
  
  In their first paper, Guldberg and Waage suggested that in a reaction such as 
  
  the "chemical affinity" or "reaction force" between A and B did not just depend on the chemical nature of the reactants, as had previously been supposed, but also depended on the amount of each reactant in a reaction mixture. Thus the Law of Mass Action was first stated as follows:
   A possible cause of this problem is that the Third Law is often stated in an abbreviated form: "For every action there is an equal and opposite reaction," without the details, namely that these forces act on two different objects. Moreover, there is a causal connection between the weight of something and the normal force: if an object had no weight, it would not experience support force from the table, and the weight dictates how strong the support force will be. This causal relationship is not due to the Third Law but to other physical relations in the system.
   Section::::History.
  
  The concept of a reversible reaction was introduced by Berthollet in 1803, after he had observed the formation of sodium carbonate crystals at the edge of a salt lake (one of the natron lakes in Egypt, in limestone):
  
  He recognized this as the reverse of the familiar reaction
  
  Until then, chemical reactions were thought to always proceed in one direction. Berthollet reasoned that the excess of salt in the lake helped push the "reverse" reaction towards the formation of sodium carbonate.
   In most cases, both mechanisms will lead to the same product, as the sites of kinetic and thermodynamic deprotonation will coincide.
  
  Section::::Scope and limitations.
   Although the concept of equilibrium is widely used across sciences, in the context of chemistry, it arises whenever a number of different states of the chemical composition are possible, as for example, in a mixture of several chemical compounds that can react with one another, or when a substance can be present in more than one kind of phase.
   In this case, the forward reaction involves the liberation of some protons from acetic acid molecules and the backward reaction involves the formation of acetic acid molecules when an acetate ion accepts a proton. Equilibrium is attained when the sum of chemical potentials of the species on the left-hand side of the equilibrium expression is equal to the sum of chemical potentials of the species on the right-hand side. At the same time the rates of forward and backward reactions are equal to each other. Equilibria involving the formation of chemical complexes are also dynamic equilibria and concentrations are governed by the stability constants of complexes.
   In some forms of mind-body dualism, a matching "factum" and "faciendum" must be present in a person's mind in order for him to act intentionally. If a person has the belief that action (A) will lead to state (S), and has the desire that state (S) obtain, then he will perform action (A). The action is directly caused by simultaneous presence of the two mental states; no further explanation is needed.
  
  According to Velleman:
  
  Section::::Bibliography.
  
  BULLET::::- Anscombe, G.E.M., "Intention (Second Edition)", Basil Blackwell, (Oxford), 1963 (first edition 1957).
   These three pairs produce combinations of colors for us through the opponent process. Furthermore, according to this theory, for each of these three pairs, three types of chemicals in the retina occur, in which two types of chemical reactions exist. These reactions would yield one member of the pair in their building up phase, or "anabolic process", whereas they would yield the other member while in a destructive phase, or a "catabolic process".
   Another crude analogy which is often used to explain attraction instead of repulsion is two people on an ice pond throwing boomerangs at each other. The boomerang is thrown away from the catcher but it circles to the catcher in the thrower's direction, both the thrower and the catcher are impulsed toward each other by the throwing and catching actions.
  
presuppositions: No motion should occur because of equal and opposite forces. An opposite and equal reaction to an action occurs on the same object.
corrections: The force is equal but the resulting acceleration which is what causes movement is dependent on the mass of the objects.  An opposite and equal reaction to an action occurs on different objects.
raw_presuppositions: No motion should occur because of equal and opposite forces. An opposite and equal reaction to an action occurs on the same object.
raw_corrections: The force is equal but the resulting acceleration which is what causes movement is dependent on the mass of the objects.  An opposite and equal reaction to an action occurs on different objects.