共查询到19条相似文献,搜索用时 93 毫秒
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讲授普通物理的力学部分时,适当地运用演示实验能激发学生思维的积极性,改善讲授理论概念的效果。“逆风行舟”是力学演示实验中较好的一个。 力的概念和牛顿第二定律是力学的核心,大学物理把中学使用的F=ma应用高等数学而改变成另一种表示式:并阐明这种新形式所表示的物理意义;又强调:力是物体与物体间的相互作用,它与物体的运动状态的变化有紧密联系。“逆风行舟”这一饶有兴趣的自然现象能很好阐明这两点。我们在1965年试制了“逆风行舟”演示设备,搬上讲台,立刻受到师生们的欢迎。近来对实践结果作了初步小结。 早在1955年《物理通报》… 相似文献
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考虑了用双车法演示牛顿第二定律实验中被忽略的因素,理论分析得出了斜面倾角与小车质量等因素的关系,并通过实验验证了小车质量发生变化后需要重新调节倾角的结论,同时指出在实验中应如何选择实验器材减小小车质量的变化对实验的影响. 相似文献
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"广义芝诺悖论"的探讨 总被引:2,自引:1,他引:1
两辆相向匀速运动的车之间有一只小鸟,在两车间来回飞行.小鸟运动速率比车的要大,其初始位置是x0.当两车最终相遇时,相遇位置就是小鸟的最终位置.现在逆向演示(回放)该过程,即小鸟从两辆车相遇位置出发而两车作相背运动.当两车回到它们的初始位置时,小鸟将回到x0点.然而,在正过程中,由于两车相遇位置(即小鸟的最终位置)实际上和小鸟的初始位置无关,因此在逆过程中,小鸟最终可以处在任意位置而未必回到x0点.由此产生悖论,称做“广义芝诺悖论”.通过建立适当的物理模型,利用运动定律,分析并最终解决了这个悖论问题. 相似文献
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牛顿第一运动定律在教材中没有安排演示实验,而通常的演示大多是在气垫导轨上进行.我们设计该演示实验不仅可以取代气垫导轨,而且取材容易,操作简单,可见度大,还可在任意方向上演示第一定律,克服了在气垫导轨上演示的固有缺点.具体介绍如下. 相似文献
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司南版教材中"模拟气压的产生"演示实验所需的实验装备在中学尚未普及,为解决这一问题,形象生动地演示该实验,利用日常易得的物品制作了"气体压强的产生"模拟演示器,详细介绍了该演示器的制作与演示方法. 相似文献
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在现有车载辅助驾驶系统中,可见光成像系统难以有效应用于夜晚、雨、雾、霾等低照度不良天气。红外成像系统有效克服了上述不足,但传统车载红外系统存在视场角小、视野盲区大的缺点。研究了超大视场红外系统的车载辅助驾驶应用,提出了基于安全距离和成像尺寸联合约束的超大视场红外系统关键参数论证方法。通过分析等距投影成像规律,建立了超大视场红外系统车载应用的安全距离约束模型和成像尺寸约束模型,以极限速度对应的探测最近距离和二维Johnson准则约束下的“发现”最远距离来验证超大视场红外车载系统的可行性,计算了视场角等关键参数。经过理论论证和分析,超大视场红外车载系统的镜头焦距/像元尺寸范围需在[276.1 521.3]范围之内。通过开展系统试验,设计了水平视场角为140°的超大视场红外成像系统,满足了对人的发现距离大于130 m的要求,进而可用于车辆辅助驾驶。 相似文献
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分析《理论力学教程》§1.3[例2]及其解答,指出该例题的解题条件不足,以及解答中存在的错误.补充阻力系数之后该例题成为适当的动力学问题,小船的动力学方程是一个变系数非线性齐次二阶常微分方程,采用数值计算方法求解其运动轨迹,讨论了阻力系数对轨迹的影响.研究表明当阻力系数越来越大时,小船的横向速度才约等于水流速度的横向分量.补充υφ=-C1 sinφ作为小船运动的微分约束,[例2]的解题条件才充足,才成为存在确定轨迹的质点运动学问题. 相似文献
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The stress induced in the Indo-Pacific bottlenose dolphin, Tursiops aduncus, by boat presence and type was investigated in a highly urbanized coastal environment, the Port Adelaide River-Barker Inlet Estuary, South Australia. The level of stress experienced by bottlenose dolphins was inferred from the distribution patterns of their dive durations. Dive duration has previously been shown to increase under boat traffic conditions, and is considered as a typical avoidance behavior. Dive durations were opportunistically recorded from land-based stations between January 2008 and October 2010 in the absence of boat traffic, and in the presence of kayaks, inflatable motor boats, powerboats and fishing boats. Subsequent analyses were based on nearly 6000 behavioral observations. No significant differences in dive durations were found between control observations (i.e. absence of boats) and boat interferences, which could erroneously lead to conclude that boat traffic did not induce any stress in T. aduncus. In contrast, the scaling exponents of the cumulative probability distribution of dive durations obtained in the absence of boat traffic and under different conditions of boat interferences show (i) that the presence of boats affected the complexity of dive duration patterns and (ii) that stress levels were a function of boat type. Specifically, the complexity of dive duration patterns (estimated by the scaling exponent ?) did not significantly differ between control behavioral observations and behavioral observations conducted in the presence of kayaks. A significant increased in behavioral stress (i.e. decreasing values of ?) was, however, induced by the presence of fishing boats, motorized inflatable boats and powerboats. This demonstrates that traditional approaches based on the analysis of averaged behavioral metrics may not be sensitive enough to detect changes in the distribution pattern of behavioral sequences, hence underestimate the potential consequences of e.g. chronic exposure to low levels of stress. It is finally emphasized that fractal analyses of behavioral variables, and in particular the analysis of their cumulative probability distribution function, may provide a non-invasive, objective and quantitative framework that can be used to assess the changes in stress response, and subsequently evaluate the welfare status of organisms under various conditions of abiotic and/or biotic stress. 相似文献
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A. Sroka 《Molecular physics》2013,111(13):2037-2045
For solid-state structures of androstan-3-one derivatives presented in Cambridge structural database (CSD), the puckering parameters for the six-membered rings were calculated to investigate the ring conformation. It was found that for the A-ring, except for typical chair conformation, the boat conformation appears very often. This conformation is also possible for the rings B and C. There are a few compounds with boat conformation of A- and B- or A- and C-ring, but simultaneous boat conformation of B- and C-ring has not been found. The methyl substituents at 10 and 13 position of the androstane-3-one as well as carbonyl group at the 3-carbon atom play a significant role in the stabilisation of the structure of androstan-3-one. 相似文献
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Superhydrophobic cotton fabric fabricated by electrostatic assembly of silica nanoparticles and its remarkable buoyancy 总被引:1,自引:0,他引:1
Yan Zhao 《Applied Surface Science》2010,256(22):6736-9531
Highly hydrophilic cotton fabrics were rendered superhydrophobic via electrostatic layer-by-layer assembly of polyelectrolyte/silica nanoparticle multilayers on cotton fibers, followed with a fluoroalkylsilane treatment. The surface morphology of the silica nanoparticle-coated fibers, which results in the variety of the hydrophobicity, can be tailored by controlling the multilayer number. Although with the static contact angle larger than 150°, in the case of 1 or 3 multilayers, the fabrics showed sticky property with a high contact angle hysteresis (>45°). For the cotton fabrics assembled with 5 multilayers or more, slippery superhydrophobicity with a contact angle hysteresis lower than 10° was achieved. The buoyancy of the superhydrophobic fabric was examined by using a miniature boat made with the fabric. The superhydrophobic fabric boat exhibited a remarkable loading capacity; for a boat with a volume of 8.0 cm3, the maximum loading was 11.6 or 12.2 g when the boat weight is included. Moreover, the superhydrophobic cotton fabric showed a reasonable durability to withstand at least 30 machine washing cycles. 相似文献