This may therefore constitute experiential support for the inference of property transmission in the case of forces. Many instances of resemblance between things occur for reasons other than direct causal connection between them. They may, for example, be independent products of the same process. It is therefore important to distinguish instances of resemblance that mark causal relations from those that do not.
White b therefore proposed some conditions that must be met for the property transmission heuristic to be applied.
In the present context, however, which is specifically object motion, just one criterion suffices. That is just that a match should be made between available kinematic information and stored representations of actions on objects. If that happens, the stored representations provide sufficient information for a judgment to be generated. In the following sections, I shall show that the property transmission heuristic accounts for the research findings that have been interpreted as evidence for the impetus theory, as well as for some findings that cannot be explained by the impetus theory.
Before that, I shall briefly discuss one example of the use of the property transmission heuristic because it has some relevance to the account that follows. The example is the launching effect Michotte, In research on this phenomenon, an animation is presented in which a moving object the launcher comes into contact with a stationary object the target , whereupon the launcher stops moving and the target starts moving.
Figure 1 is a schematic representation of a typical sequence of events in a launching stimulus. The occurrence of this impression depends, however, on resemblance between the properties of the motion. The impression tends to be most reported when the speed of the target after contact is similar to the speed of the launcher before contact Michotte, ; Natsoulas, Schematic representation of a launching effect stimulus. Panel a shows the first frame of the stimulus, with the target the white disc stationary in the centre of the frame and the launcher the black disc entering from the left.
Panel b shows the launcher approaching the target one. Panel c shows the frame in which the launcher contacts the target, and in panel d , the target is in motion toward the right edge of the frame and the launcher is stationary at the point of contact. The problem with this is that differences of speed are not uncommon in real collisions.
If the target is more massive than the launcher, then it will tend to move much more slowly than the launcher Runeson, This, I have argued, represents the property transmission heuristic in perceptual processing; it is a kind of reverse use of the heuristic. Instead of using the heuristic to infer unobserved motion properties, the appearance of property transmission in the observed motion properties is used to make a perceptual interpretation in terms of causality: The kinematics of the target when it begins to move resemble those of the launcher when it contacted the target, therefore the launcher caused the target to move.
White showed that a similar phenomenon holds for a different kind of visual impression of causality, pulling: Two objects must be moving, to a close approximation, at the same speed and in the same direction for one to be seen as pulling the other.
The radius of action has some relevance to the property transmission interpretation of object motion judgments, as I shall show later. In an application to findings relevant to the impetus theory, the following propositions are most relevant. If the judge either does not have a theory or does not access one that is possessed, then he or she may be in a state of uncertainty. In that state, the property transmission heuristic is used to generate a judgment.
In general, the moving object is judged to acquire a force that is related to the force that was applied to make it move.
Where the trajectory of the object is uncertain, it will also be predicted to acquire salient properties of the motion of the causal object or system. Thus, the property transmission hypothesis predicts judgments about both the dynamic and kinematic properties of objects whose motion is judged to have been caused by another object acting on them: The object is judged to acquire force that is proportional to the force exerted on it by the causal object, and where the motion properties of the object are not known, it is also judged to acquire salient kinematic properties of the causal object.
In this section, I review each of the findings that have previously been interpreted as support for the impetus theory and show how the actions-on-objects approach and the property transmission heuristic account for them. I shall also show that the present account can be applied to some judgmental phenomena that fall outside the scope of the impetus theory.
Caramazza, McCloskey, and Green presented diagrams of a pendulum showing the bob and string at various points in the swing: These are shown in Fig. Participants were asked to draw a line representing the path the bob would take if the string was cut at that point in the swing. Objectively, whenever the bob is in motion, after being cut it should follow a parabolic path that begins in the direction of its prior motion i.
If the string is cut at the apex of the swing, as in Problem A of Fig. Pendulum problems from Caramazza et al. Each problem shows a different location where participants are told to imagine that the string is cut. Arrows indicate directions of motion of the pendulum, and dotted lines indicate the path of the bob and the extremes of the trajectory. Here, participants judged that the bob would continue along its original arc for a while, as if it were still attached to the string, and then fall straight down.
This error can also be explained by the property transmission hypothesis. In this explanation, the causal system is seen as acting on the bob with force; the force of the causal system is believed to be transmitted to the bob. The salient feature of the kinematics of the causal system is the curvilinear trajectory, and the curvilinear trajectory is imparted to the bob as a case of property transmission.
The property transmission heuristic would therefore predict a tendency to judge that the curvilinear trajectory would be perpetuated beyond the point where the string is cut. In effect, the causal force of the launcher weakens as the target moves away from the launcher. The transition point is the radius of action. This same notion can be seen as applied to the motion of the bob. Beyond a certain point, the bob goes beyond the radius of action.
At that point, it is judged to have lost its acquired force, and the concomitant curvilinear motion. The only force judged to be acting on it is gravity, so it is predicted to move straight down. The property transmission heuristic can also explain two of the other classes of errors identified by Caramazza et al. For example, in Fig. In this case it appears that the line of the string is the feature of the causal system that was salient for participants, and they judged that the bob would continue it by property transmission.
This can be interpreted as reflecting a belief that no force is acquired by the bob on the grounds that the causal system is not exerting force on it. If the bob acquires no force, then the only force acting on it is gravity, so it falls straight down.
This interpretation will be explained in more detail in the section on the straight-down belief below. The property transmission heuristic does not explain those judgments, nor the correct judgments. If people have specific acquired beliefs, such as correct Newtonian beliefs, then they will not be in a state of uncertainty, and the property transmission heuristic will not be used. In essence, then, the property transmission heuristic applies when people do not have, or do not apply, acquired knowledge correct, incorrect, or incomplete about the system in question.
To explain motion, the force of the causal object or system is judged to be transmitted to the effect object along with whatever kinematic properties of the causal system are salient to the judge. If the causal system is not judged or believed to be exerting force on the effect object, then the heuristic will not be used, and the effect object will not be judged to acquire the force of the causal object.
McCloskey, Caramazza, and Green set three problems in which diagrams were presented of, respectively, a C-shaped tube, a spiral tube, and two C-shaped tubes positioned in mirror symmetry with their mouths adjacent to each other. The diagrams are shown in Fig. Participants were told that the tubes were lying on a flat surface and that a ball inserted into one end of the tube is shot out of the other end at high speed.
They were asked to draw the path that the ball would take on exiting the tube. A majority of the participants drew correct, straight Newtonian trajectories. Others, however, drew curved trajectories that continued, to some degree, the curve of the tube. Interviews revealed that. Curved-tube problems from McCloskey et al. Arrows indicate the points at which participants are informed that a ball is inserted into a tube.
McCloskey and Kohl presented a flat surface with a curved path marked on it and asked participants to push a puck so that it stayed within the confines of the path. The explanation for belief in curvilinear trajectories in these situations is similar to that for the Type 6 error on the pendulum problem Caramazza et al.
An initial force is applied to set the ball in motion, and it is at first constrained to move in a curved path because of the tube. Under conditions of uncertainty, the property transmission heuristic comes into play. The curved shape of the tube is the salient feature of the causal system, because it determines the path taken while the ball is within the tube, so the curve is judged to be transmitted to the projectile as a kinematic feature.
As before, the acquired force and the curvilinear trajectory gradually dissipate. In the latter case, this results in a progressive straightening of the trajectory, that was noted by McCloskey et al.
The property transmission heuristic will not be used when features of the problem elicit knowledge of familiar systems. These children were in possession of a theory of object motion, that balls roll in straight lines, so they were not in a state of uncertainty and would not resort to the property transmission heuristic.
McCloskey et al. This is shown in Fig. The diagram identified a point at which the string broke, and participants drew the trajectory that they thought the ball would then take. Interviews again revealed that most of the latter group thought that the ball acquired a force that caused it to continue in curvilinear motion, and that the acquired force would gradually dissipate, eventually resulting in motion in a straight line.
Footnote 3. Twirling-ball problem from McCloskey et al. The straight line indicates a string held at one end by a person who is twirling it above the head.
A metal ball moves in a circular path indicated by the circle , with the direction of motion indicated by arrows. The property transmission heuristic explains the incorrect curvilinear trajectory extrapolations here.
The person twirling the ball is applying force to the ball and constraining it to move in a circle. The kinematic properties of the causal system are transmitted to the ball while the string is intact. This curvilinear motion is the salient feature of the causal system and, under conditions of uncertainty, it is judged to be transmitted to the ball, not only when the ball is attached to the actor by the string, but also after the string is broken.
As in the curved tube problems, the curvilinear motion gradually dissipates as the motion of the ball continues. Strictly speaking, there is no need to postulate a judgment that the projectile acquires force from the causal system, either here or in the curved-tube problems.
Salient features of the kinematics suffice to generate a trajectory extrapolation using the property transmission heuristic. This is evident in the verbal reports of participants, which frequently refer to the acquired force of the projectile McCloskey et al. The acquired force and the curvilinear kinematics go together, but only because the property transmission heuristic predicts both of them.
Most of the remainder gave the correct answer that the object would follow a parabolic trajectory because of its forward momentum combined with the gradual increase in vertical speed due to gravity. In Fig. The rod and ball were carried by the conveyor at 50 mph, and the ball was released in the position shown in the figure.
Panel B of Fig. The proportions of straight-down responses were higher in some other problems in which a projectile was dropped from a moving carrier. In their Experiment 1, McCloskey et al. The straight-down belief is therefore specific to the case in which the projectile is passively carried and released by the carrier, and does not generalize to cases in which the projectile is pushed horizontally, as in a kicking or launching interaction.
Further evidence for the belief has been reported Krist, ; Whitaker, This includes a study in which participants being rolled in wheelchairs attempted to drop a tennis ball to hit a target on the ground Krist, Conveyor panel a and level ramp panel b problems from McCloskey et al. In the conveyor problem, the horizontal line represents a conveyor belt.
The vertical line depending from the conveyor belt represents a metal rod, with a metal ball attached to the end by an electromagnet. Participants are told that the conveyor is moving at 50 mph and that the ball is released at the point shown in the diagram. In the level ramp problem, the horizontal line represents a level ramp and a metal ball is shown on the level ramp. Participants are told that the ball is pushed so that it is moving at 50 mph when it reaches the end of the level ramp.
The explanation for these results under the impetus theory is that objects are believed to acquire impetus only from direct pushes, kicks, or similar application of force; merely being carried and then released does not impart impetus to the object. If the object has no impetus, the only force judged to be acting on it is gravity, and it is therefore judged to fall straight down.
The present account resembles the impetus account inasmuch as the causal system is not judged to be exerting any force on the object when it merely releases the object, so the object does not acquire any force from the causal system. Similarly, because no force is exerted on the object by the causal system, the primary condition for applicability of the property transmission heuristic is not met, and therefore the motion properties of the causal system are not judged to be transmitted to the object.
If the object acquires neither force nor kinematic properties from the causal system, then the only force believed to be acting on it is gravity, and it is therefore judged to fall straight down. This is the problem described at the beginning of the article. Whitaker included another version of this problem, in which a bullet is fired horizontally from a gun at the same moment at which a heavy ball at the same height as the gun is dropped.
Both objects are acted on by gravity and by no other forces, so, ignoring the curvature of the Earth and unevenness in the terrain, they reach the ground at the same time. Verbal justifications for this and for the hunter-and-monkey problem indicated a belief that the bullet would travel horizontally for a certain distance before beginning to fall.
These answers can be explained by the property transmission heuristic. The firing of the gun exerts force on the bullet. This acquired force gradually dissipates, and as the bullet slows the radius of action is reached, and the bullet starts to fall. By contrast, the ball is merely dropped, which as we saw in the previous section is not interpreted as the exertion of force on the ball. Because of the belief that the ball starts to fall sooner than the bullet does, the ball is judged to reach the ground first.
Clement asked participants to draw the forces acting on a coin that had been tossed up. People said that this force must be stronger than gravity at first, otherwise the coin would not go up. Kozhevnikov and Hegarty , Exp. With air resistance explicitly present, With air resistance explicitly out of consideration, the proportion claiming that the lighter object would get there first was reduced to Kozhevnikov and Hegarty claimed that the impetus theory predicts that the heavy object will lose impetus more quickly than the light object, on the grounds that gravity is believed to pull heavy objects down more quickly than light objects.
However, this would depend on whether people believe that gravity acts on ascending objects at all. As we saw in discussion of the hunter-and-monkey problem, some people believe that gravity only begins to affect an object when its impetus has diminished to zero or very little Whitaker, Furthermore, the proportion of participants endorsing the impetus response was unusually high— This suggests that there may be a different explanation for this result. The property transmission heuristic does not apply to this kind of judgment, since the heuristic concerns motion properties being imparted to an object by another object, not how those motion properties change after the causal relation has occurred.
However, the actions-on-objects perspective still provides a means of interpreting the results. Consider the results of two studies by Rohrer , on the motion of objects down inclines with undulating contours. Figure 6 shows the diagram of the undulating courses used by Rohrer Participants were asked to suppose that two marbles were released, one on course A and one on course B, and they had to judge which marble would be moving faster at the point where the courses are connected by the vertical line.
Speed problem from Rohrer Curved lines represent two inclines, with two marbles released at the point shown by the circle.
One marble takes path A , and the other takes path B. Participants are asked to judge which marble, if either, is rolling faster at the points connected by the vertical dotted line. At the indicated point, course A is on an upward slope, whereas course B is on a downward slope. However, the net vertical drop at that point is greater on course A than on course B, as can be seen from the fact that course A is running below course B at that point.
This means that the marble on course A will be moving faster than the marble on course B. More than half of the participants judged, however, that marble B would be moving faster than marble A. This reflects a judgment that the speed of the object at a given point depended on the slope of the incline at that point. Anticipating the actions-on-objects theory, Rohrer argued that the slope-speed judgment is derived from considerations of objectively irrelevant dynamic features of the situation.
When we try to push an object uphill, the resistance of the object being pushed is proportional to the slope. For the same reason, it is harder to climb a steep hill than a shallow one.
In other words, people judge the speed of the object from a consideration of how difficult it would be to stop the object or push it up the slope at that point. This exemplifies the main argument made here: Explicit judgments about object motion are based on experiences of acting on objects, which yield information about forces.
Rohrer extended this argument about the relation between resistance, slope, and speed to a consideration of mass. I shall first summarize the results of some studies on judgments about the motion of objects that have different masses. Kozhevnikov and Hegarty found that the rate of endorsement of this belief depended on air resistance, and dropped to This explicit reference to air resistance could have helped to remind people of the Newtonian theory that they might otherwise have neglected, but this possibility has not been tested yet.
Whitaker asked students who had been educated in physics about two balls weighing 5 lb and 50 lb, both dropped at the same time. Proffitt, Kaiser, and Whelan asked people to judge what would affect the speed of a wheel rolling down an inclined plane, and they found a tendency to judge that a heavier object would roll down faster than a lighter one. These erroneous judgments about objects moving under gravity are not predicted by the impetus theory, because falling objects are not believed to have impetus.
Footnote 4 Rohrer argued that these are also cases in which speed is judged from dynamical considerations. The more massive object offers more resistance than the lighter one: It is harder to stop it if it is in motion, and harder to push it up an incline. Therefore, a fallacy similar to the resistance-speed fallacy applies: If mass predicts resistance, and resistance predicts speed, then mass predicts speed. Rohrer found support for the resistance argument by priming participants with a question about resistance before they did the speed judgment task, and he found a greater tendency for the slope-speed belief to occur, by comparison with a control group.
This provides a possible explanation for the results found by Kozhevnikov and Hegarty Participants were again reasoning about the difficulty of moving an object up, though in this case the task was throwing the object rather than pushing it.
It is harder to throw a heavier object up at a given velocity than it is to throw a lighter object up at the same velocity. The deceleration of the object is predicted by the amount of force required to throw it. If mass predicts resistance and resistance predicts speed, then mass predicts speed. The heavier object is judged to decelerate more than the lighter one, and therefore to take longer to reach a given height, because the judgment is based on the haptic experience that it is harder to throw the heavier object up at a given speed than it is to throw the lighter one.
All of these findings—those of Rohrer for undulating slopes, those of Champagne et al. Judgments about kinematics are based on dynamical considerations that are ultimately derived from experiences of acting on objects. If the impetus theory and the property transmission heuristic and the actions-on-objects approach in general are competing accounts of judgments about moving objects, it is important to find phenomena that can be explained by one and not by the other.
The research to be discussed under this heading is an example, because these findings cannot be explained by impetus theory but can be explained by the property transmission heuristic.
Participants were asked to mark the point in the trajectory where the maximum speed of the ball would occur. Objectively that point comes immediately after the release of the ball from the hand. At that point, only gravity and air resistance are acting on the ball. Because the ball has an upward component to its motion, gravity tends to slow the ball down. When the apex is reached, the ball starts to accelerate under gravity, but its speed on reaching the target is not as great as its speed on leaving the hand because of the effects of air resistance.
However, the mean position chosen by participants was just before the apex was reached, not far from the slowest point of the trajectory. Two-dimensional animation did not improve judgment: Animations in which the ball accelerated after leaving the hand were judged to look natural.
Presenting 2-D animations in perspective to represent the third dimension resulted in some improvement: The correct velocity profile was rated higher than the one with initial acceleration, but the latter was still rated higher than a profile with initial deceleration.
Throwing problem from Hecht and Bertamini Participants are told that the person on the left throws a ball to the person on the right. The continuous curved line and the straight dotted line represent two trajectories of the ball. Hecht and Bertamini pointed out that there is nothing in the impetus theory or in any other pre-Newtonian theory of motion that would explain this belief. If the throw imparts an acquired force to the projectile, in the impetus theory that force starts to dissipate immediately.
The ball would therefore start to slow down immediately and would never go through a phase of increase in speed before the apex is reached. However, it is far from clear why this should happen, and in fact the hypothesis does not explain the judgmental phenomenon at all, but merely redescribes it. Belief that the ball continues to accelerate after being released from the hand can be explained under the actions-on-objects account as an instance of the property transmission heuristic.
This belief about projectile motion, and the explanation for it, may have some relevance to the topic of the previous section, throwing objects upward. The belief implies that people may judge that a ball thrown upward also continues to accelerate after leaving the hand. If that is the case, then the rate of acceleration should be negatively correlated with the mass of the projectile. The reasoning is essentially the same as the resistance-speed fallacy: A heavier object offers more resistance to the force applied to it than a lighter object does, so its judged acceleration after leaving the hand should be less.
Therefore, it will take longer to reach a given height. Judgments of speed and changes in speed have not been investigated in this context, but much could be learned by doing so.
The actions-on-objects account explains the judgmental tendencies and the belief in acquired force by assimilating them to a general account of the understanding of object motion and its causes. Our understanding of forces in interactions between objects is based on our experience of exerting force and producing outcomes when we act on objects.
This directly predicts some judgmental phenomena, such as the erroneous speed judgments reported by Rohrer and erroneous beliefs about the behavior of objects of different masses when they are thrown straight up Kozhevnikov and Hegarty, , that cannot be explained by the impetus theory. The actions-on-objects account provides the grounding for the property transmission heuristic, and this heuristic accounts for the remaining findings: Salient features of the forces exerted by the causal object, and the kinematics of the causal object, under conditions of uncertainty are judged to be transmitted to the effect object.
This accounts for numerous findings of judged curvilinear trajectories, such as in the C-tube problem McCloskey et al. Explaining explicit judgments about object motion in terms of a theory of impetus is unsatisfactory because the existence of the impetus theory itself is unexplained. Kozhevnikov and Hegarty argued that the impetus theory is derived from everyday experience, where moving objects do tend to slow down because of friction and air resistance.
This argument fails for several reasons. First, everyday experience does not account for extrapolation of curvilinear trajectories in the C-tube and spiral problems McCloskey et al. Second, experience yields information about kinematics, and that is enough for predictive purposes. There is no need to abstract a theory at all if kinematic regularities suffice for practical needs. Third, if we are going to abstract a dynamic theory of motion, why not abstract the correct one, that objects slow down because of friction and air resistance?
Hubbard argued that the impetus theory involves fewer parameters and therefore functions well as a heuristic with a reasonable level of accuracy.
Simplicity is certainly an advantage, but that does not explain why a theory postulating an unobserved property of moving objects would be abstracted from experience of friction and air resistance, which are properties not of the object but of the medium or other objects with which the moving object is interacting.
Fourth, the everyday-experience hypothesis was disconfirmed by an experiment by Krist in which participants dropped a ball to hit a target while being rolled in a wheelchair. In one condition, the ball was a tennis ball, and in another the ball was made of cotton wool, which would tend to fall straight down because its horizontal motion would be quickly arrested by air resistance.
However, participants in both conditions were equally likely to report the straight-down belief, which led them to try to drop the ball when directly over the target. Everyday experience should tell us that tennis balls and cotton balls behave differently when dropped from a moving carrier, but apparently, for children at least, it does not.
These considerations are not sufficient to disconfirm the impetus theory—it may be that not enough is yet understood about the origins of notions of impetus—but it leaves the impetus account at a disadvantage. The approach taken here has the advantage that it assimilates evidence of judgments about object motion to a general account of the understanding of how motion is externally caused. The actions-on-objects account and the property transmission heuristic have been used to explain numerous findings in several domains of judgment White, b , , and the set of findings reviewed here, concerning acquired force and extrapolated trajectories, can be understood as belonging to the general family of phenomena explained by the actions-on-objects account and the property transmission heuristic.
One apparent disadvantage of the present approach is one that is likely to be shared by any attempt to explain explicit judgments about object motion. Most of the remaining participants got the correct answers. The present approach, like the impetus theory, does not explain the large proportion of correct answers obtained in most studies. Explicit judgments are open to influence from acquired knowledge, such as education in Newtonian physics.
In the present account, the property transmission heuristic is used only under conditions of uncertainty. Thus, if a theory of object motion has been acquired and is accessed in the judgment situation, there is no uncertainty, and the property transmission heuristic will not be used. Of course, the acquired knowledge on which judgment may be based does not have to be the correct physical theory.
Young children appear to operate with a different kind of general theory, that objects move in straight lines. If straight-line motion is their theory, then they are not in a state of uncertainty, and will not employ the property transmission heuristic. Thus, in the present account, the property transmission heuristic, and the actions-on-objects theory in general, explains most erroneous judgments as being made under conditions of uncertainty, and the proposition that uncertainty does not arise when the judge activates an acquired theory of motion explains both the correct answers or most of them; Whitaker, ; Yates et al.
A second alternative means of generating judgments will be discussed in the section on mental simulation. The problem with this use of the property transmission heuristic is that it is close to being cherry-picking. Despite this, it is still important to stipulate how the property transmission hypothesis can be falsified. There are two answers to this: Conditions for falsification were met in the experiments reviewed above, and the account generates novel predictions that can be tested.
In some of the studies discussed, participants drew trajectories. An example is the study of curved-tube problems by McCloskey et al. In this case, a straight-line trajectory that continued the direction that the object would have at the exit of the tube could be interpreted as supporting the hypothesis of use of the correct acquired theory. A trajectory that curved, at least initially, in the same direction as the curve in the tube could be interpreted as supporting the hypothesis of use of the property transmission heuristic.
One would be a straight line in any direction other than the one that the object would have at the exit of the tube, and the other would be a trajectory that curved in the opposite direction from that of the curve of the tube. I am ignoring more bizarre possibilities, such as trajectories with reversals of direction.
These extrapolations could have occurred but did not. Similar observations can be made about other studies in which trajectories were extrapolated by participants e. In other studies, participants were presented with three or more possible answers and chose one. For example, in a study of the twirling-ball problem by McCloskey and Kohl , Exp.
One of these was the correct answer, the choice of which would be interpreted as supporting the hypothesis of use of an acquired theory. Two of the trajectories curved in the same direction as the rotation of the system before the string was cut, and choice of these would be interpreted as supporting the hypothesis of use of the property transmission heuristic.
Two other trajectories were straight lines in the wrong direction, and a third was a trajectory that curved outwards, in the direction opposite the direction of rotation of the system before the string was severed. The hypothesis could have been falsified in this experiment, but it was not; only a small minority of responses are not explained by it.
The present account generates numerous predictions for judgments of object motion. I have already shown that the present account predicts judgmental phenomena that fall outside the scope of the impetus theory. These include predictions for the behavior of objects rolling down inclined planes Proffitt et al.
Other phenomena captured by the present account have been reviewed by White Forces result from interactions! As discussed in Lesson 2 , some forces result from contact interactions normal, frictional, tensional, and applied forces are examples of contact forces and other forces are the result of action-at-a-distance interactions gravitational, electrical, and magnetic forces. According to Newton, whenever objects A and B interact with each other, they exert forces upon each other.
When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body. There are two forces resulting from this interaction - a force on the chair and a force on your body. These two forces are called action and reaction forces and are the subject of Newton's third law of motion. Formally stated, Newton's third law is:.
The statement means that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the forces on the first object equals the size of the force on the second object. The direction of the force on the first object is opposite to the direction of the force on the second object. Forces always come in pairs - equal and opposite action-reaction force pairs. A variety of action-reaction force pairs are evident in nature.
Consider the propulsion of a fish through the water. A fish uses its fins to push water backwards. But a push on the water will only serve to accelerate the water. Since forces result from mutual interactions, the water must also be pushing the fish forwards, propelling the fish through the water.
The size of the force on the water equals the size of the force on the fish; the direction of the force on the water backwards is opposite the direction of the force on the fish forwards. For every action, there is an equal in size and opposite in direction reaction force.
Action-reaction force pairs make it possible for fish to swim. Consider the flying motion of birds. A bird flies by use of its wings. The wings of a bird push air downwards. Since forces result from mutual interactions, the air must also be pushing the bird upwards. The size of the force on the air equals the size of the force on the bird; the direction of the force on the air downwards is opposite the direction of the force on the bird upwards. This study examined the difficulties posed by conflicting formal and informal definitions of terms in mechanics for Grade 6 students aged approximately 12 years old.
Students were asked to complete the following questionnaire: 1. Describe meanings of each word. Give examples to characterise meanings. Describe a process using each of the words at least once.
Many students think forces can only be exerted by living things and some machines, but not by inanimate objects Forces and Motion. Diagnostic Resources The following worksheets may help to identify whether students hold this particular misconception. View Resource.
How can the floor make a force? Minstrell, J. The Physics Teacher, 20 1 , Gunstone, R. Science Education, 65 3 , Finegold, M. International Journal of Science Education, 13 1 , Clement, J.
Journal of Research in Science Teaching, 30 10 , Terry, C. Physics Education, 20, Gilbert, J.
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