共查询到20条相似文献，搜索用时 482 毫秒
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利用极坐标系是解决平面内绕定点转动问题的“通法”.本文介绍了平面极坐标系及物体在极坐标系中的描述,以竞赛中常见的拉船模型、天体运动和平面追击问题为例,介绍极坐标系的具体应用. 相似文献
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甘宗桐 《成都教育学院学报》2005,19(12):132-134
力学规律的建立和应用都离不开参考系、惯性系、坐标系.参考物(系)的确定,是确切地观察和描述物体运动的前提,物体的运动和运动规律只能在确定的参考物(系)下描述;若质点对某个参考系的运动服从牛顿第一、第二定律,这个参考系就是惯性系;若质点对某个参考系的运动不服从牛顿第一、第二定律,这个参考系就是非惯性系.要精确地描述物体的运动,必须精确地描述物体的位置、位移,只能在坐标系下解决问题. 相似文献
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物体以v0初速度在离地高为h的地方做平抛运动,以经过抛出点的竖直方向为y轴,地面沿v0方向为x轴,建立坐标系,则运动物体轨迹关于时间t的参数方程为:x=v0t,y=h-21gt2.消去t得y=-2vg02x2 h.这就是平抛运动的轨迹方程.对照以y轴为对称轴的抛物线方程一般式y=Ax2 B知,平抛运动轨迹为 相似文献
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"轨迹"问题是高中物理竞赛中一类很重要 的热点问题,由于缺乏正确的解题思路,这类问 题常成为学生在物理竞赛学习中较难解答的问 题。本文通过结合具体教学实例,就物理竞赛中 运动物体轨迹问题的处理方法作一教学小结。 1 运用"数学解析法"求解运动物体轨迹 1.1 运用直角坐标求解 对于受到某种几何约束的运动物体,常运用 直角坐标求解运动轨迹,基本思路是:(1)建立 坐标系(直角坐标系或极坐标系),确定运动物体 的坐标;(2)运用物理规律建立有关物体坐标的 运动方程;(3)运用运动物体几何约束关系,定 相似文献
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李庆忠 《数理化学习(高中版)》2003,(9)
物体运动的轨迹可根据参数方程分析、确定,如:确定平抛物体运动的轨迹,建立如图1所示的坐标系,则物体运动的参数方程为:消去参数t,可得: 此方程为抛物线方程,故平抛物体运动的轨迹为抛物线. 例1 半圆光滑槽质量为M,半径为R置 相似文献
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在研究运动学和动力学的问题时,都涉及参照物和坐标系的选取,因为任何物体的运动都是相对一定参照物而言的。对同一问题,选用不同的参照物或坐标系,对运动的描述会有所不同,因而,巧妙地选取参照物和坐标系可以简化计算过程,达到事半功倍的目的。 相似文献
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陈建国 《赣南师范学院学报》1995,(6)
一个物体真有无穷多个长度吗？─—关于狭义相对论的一个流行观念质疑陈建国（江西省社会科学院南昌，３３０００６）１关于狭义相对论的一个流行观念是：一个物体有无穷多个长度根据狭义相对论，一个物体在静止坐标系中的长度为Ｌ＿０，则在运动坐标系中的长度Ｌ＿１＝式... 相似文献
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The blocking phenomenon was investigated in the sexual response system of male Japanese quail. Access to a live female quail served as the unconditioned stimulus (US). The same audiovisual cue served as the pretrained stimulus in all of the experiments. Following asymptotic conditioning of the audiovisual cue, a second conditioned stimulus (CS2) was added. In Experiment 1, CS2 was a rectangular wood block that had little or no resemblance to a female quail and could not support copulatory behavior. In Experiment 2, CS2 was a terrycloth object that had no quail parts but could support copulatory behavior, and, in Experiment 3, CS2 was a terrycloth object that had a taxidermically prepared head of a female quail added. The terrycloth-only object supported more rapid conditioning than did the wood block, but the blocking effect was obtained with both kinds of stimuli. Approach responding to the terrycloth + head object required pairing it with copulatory opportunity, and the terrycloth + head object supported at least as rapid conditioning as did the terrycloth-only object. However, responding to the terrycloth + head object was not blocked by the pretrained audiovisual cue. These results indicate that the blocking effect occurs in sexual conditioning even with stimulus objects that can support copulation. However, the addition of species-typical head cues to an object makes that object such a powerful stimulus that conditioned approach responding to it cannot be blocked by a previously conditioned arbitrary audiovisual cue. 相似文献
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在自然环境中,背景往往对识别环境中的物体起着非常重要的作用。已有研究表明物体与背景的语义一致性会影响对物体和背景的知觉。研究引入物理性质的一致性（旋转角度）这一变量,采用二因素的混合实验设计和直接命名法考察物理性质的一致性和语义一致性对物体和背景知觉的影响。结果发现,语义一致性主效应显著,在物体与背景语义一致性条件下对其进行识别的正确率高于语义不一致性条件下的识别正确率;物理性质一致性主效应也显著,物理性质一致条件下对物体和背景识别的正确率显著高于不一致性条件下的,而且,识别的正确率随着旋转角度的增大而降低;二者之间的交互作用不显著,这意味着物理性质一致性与语义一致性是独立影响真实场景中物体识别和背景识别过程的。 相似文献
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Eight- to 12-month-olds might make A-not-B errors, knowing the object is in B but searching at A because of ancillary (attention, inhibitory, or motor memory) deficits, or they might genuinely believe the object is in A (conceptual deficit). This study examined how diligently infants searched for a hidden object they never found. An object was placed in A twice, and then in B. In a different task the object was placed beside A twice, and then in B. Infants made more A-not-B errors in the former task, and perseverating infants searched diligently in A rather than in B. Infants seemed to believe the object was in A, suggesting that both a conceptual deficit and ancillary deficits account for A-not-B errors. 相似文献
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What supplies the concepts in causal inferences in story comprehension? This question was examined in 5 experiments. Elementary school children and college students listened to stories containing a "premise" sentence describing a character's intent in initiating a series of actions, followed by an unexpected "outcome." After each story, the subjects were asked inference questions about the reason for the outcome (Experiments 1-4) or asked to explain the outcome (Experiment 5). In the various experiments, the availability of object concepts for an inference was manipulated by providing 0 or 2 clues preceding the outcome, additional filler information that diluted the clue information, a mention of an object in the premise or no mention, and an object title for each story or no title. The results suggested that the availability of an object concept in sentences prior to the outcome was a critical determinant of whether an object inference occurred, especially for children. Given availability, the thematic prominence of the object influences whether the object will be used in an inference. 相似文献
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《Early childhood research quarterly》2006,21(3):360-373
This study investigated the role of word knowledge and spontaneous labeling of familiar objects in free sorting object categorization by 16–23-month-old children. General vocabulary was related to categorization on particular tasks involving both familiar and unfamiliar objects. Object labeling was associated with categorization when familiar objects of a given kind were identical. Spontaneous object labeling was also the only predictor of non-familiar object categorization, beyond the effects of age and vocabulary. The pattern of results suggests that spontaneous object labeling during free sorting is a reflection of the child's heightened involvement in the challenge of category discovery, thus perhaps facilitating object categorization. The findings reinforce the importance of teachers engaging toddlers in interactive object naming and world learning, as well as encouraging self-narration. 相似文献
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Syntax has been noted to play an important role in word learning in English; it distinguishes the fundamental conceptual difference between individuals (coded as proper nouns), nonindividuals (coded as mass nouns), and classes of individuals (coded as count nouns). The Japanese language does not have grammatical markers flagging the distinctions between count nouns and mass nouns, between proper nouns and common nouns, or between singulars and plurals. How Japanese 2- and 4-year-olds assign meaning to novel nouns associated with familiar and unfamiliar animals and inanimate objects was studied in the research reported here. When a novel label was given to an unfamiliar object, children assumed it to be a name for a basic-level object category whether the referent was an animal or an inanimate object. If the named object already had an established name, and if the object was an inanimate object, the children mapped the noun to a subordinate category. When the named object was an animal, however, they tended to interpret the label as a proper name. These results demonstrated that in the absence of useful information from syntax, 2-year-old Japanese children are able to fast map a noun to its meaning by elegantly coordinating word-learning biases and other available sources of information. 相似文献
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We examined the role of object kind familiarity (i.e., knowledge of a count noun for an object) on preschoolers' sensitivity to the relation between a novel word's form class (adjective or count noun) and its reference (to a material kind-property or to an object kind). We used a forced-choice match-to-target task, in which children learned a word for one object (e.g., a metal cup), and then chose between 2 other objects. One was from the same object kind but a different material kind (with different related properties, such as color and texture; e.g., a white plastic cup); the other was from a different object kind but the same material kind (with the same related properties; e.g., a metal spoon). In Experiment 1, children learned either a count noun (e.g., "This is a zav") or an adjective (e.g., "This is a zav one"). Within each form class, we crossed the familiarity of the referent object kind (familiar and unfamiliar) with the age of the children (2- and 4-year-olds). The principal finding was that in interpreting an adjective, 4-year-olds were more likely to choose the object sharing material kind with the target if the target was familiar than if it was unfamiliar. No such familiarity effect was evident among 2-year-olds. In Experiment 2, we employed a more unambiguously adjectival frame (e.g., "This is a very zav-ish one"), and replicated the results of Experiment 1. We interpret the results in terms of 2 proposed word learning biases: one that learners initially expect any word applied to an unfamiliar object to refer to a (basic-level) kind of object, and a second that learners prefer words to contrast in meaning. We consider several interpretations of the observed age difference. 相似文献
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Perception of the manner in which objects may be grasped was examined in a series of experiments with adults and 10-month-old infants; visuomotor adjustment in hand orientation before making contact with objects served as the index throughout. In the first experiment, infants modified their hand orientation to match more closely the long axis of an object. They did so even though the target object could have been grasped by either end with hands oriented orthogonally to the long axis of the object. In two subsequent experiments involving reaching through narrow apertures to grasp the target, anticipatory adjustments in hand posture were evident for adults but not for infants. However, anticipatory adjustments by infants, sometimes appropriate and sometimes inappropriate, were made when the object was of such a size that it could neither be grasped nor retrieved through the aperture. In the final experiment, infants directed their hands first toward a handle, the only graspable part of an object, and oriented their hands so as to be nearly parallel with it prior to contact. This was the only orientation in which a grasp was possible. It was concluded that infants at 10 months respond more appropriately to object properties than to surface apertures that place limitations on how an object may be grasped. 相似文献
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Copulatory behavior rarely occurs in response to an arbitrary inanimate object. However, such behavior can provide important information about the stimulus control of copulatory behavior. In the present study, male Japanese quail were administered 15–20 conditioning trials that included exposure to an inanimate object and an opportunity to copulate with a live female quail. For some subjects, the stimulus object was always entirely covered with terrycloth. For other birds, the stimulus object contained a taxidermically prepared head and neck of a quail hen. Fading consisted of gradually covering up the neck and then the head portions of the stimulus object over successive trials. After conditioning, all subjects were tested with the entirely covered object. The fading procedure facilitated the conditioning of copulatory behavior to the entirely artificial object. In subjects that received the fading procedure, learning did not depend on pairings of the stimulus object with copulatory opportunity. The results are discussed with respect to an associative mediation mechanism. 相似文献
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Infants’ transfer of information from pictures to objects was tested by familiarizing 9‐month‐olds (N = 31) with either a color or black‐and‐white photograph of an object and observing their preferential reaching for the real target object versus a distractor. One condition tested object recognition by keeping both objects visible, and the other tested object representation by hiding both objects. On visible trials, infants reached more for the distractor, indicating they recognized the target object from its picture. On hidden trials, infants reached more for the target object, suggesting they formed a continued representation of the object based on its picture. Photograph color had no effect. Infants thus show picture‐to‐object transfer by 9 months with preferential reaching, even with black‐and‐white pictures. 相似文献