关于变质量系统的动能定理

同讨论变质量物体运动方程一样,用动能定理处理变质量问题时,通常也有两种方法:一种是以变质量质点(主体)为研究对象,由此可导出变质量质点的动能定理[1];另一种是以变质量系统(二质点系)为研究对象,由此可导出变质量系统的动能定理.应该说,两种方法都是可行的.     

浅议动能定理的隐含条件

浅议动能定理的隐含条件裴晓云（云南省国防工业学校昆明６５０２２２）动能定理是解决力学问题的重要工具．动能定理在解决力学问题时，较牛顿运动定律方便、实用．正因为如此，有时人们在应用动能定理解题时，会不顾其成立条件，而产生违反能量守恒的结果．下面就这个问...     

分运动可以应用动能定理

学生学完动能定理后, 经常会对分运动应用动能定理求解, 有些文章将学生的这种解法称为“ 动能定 理的分量式” . 有的文献认为动能定理没有分量式; 有的文献认为在正交系中, 动能定理可以有分量式. 而笔者则认 为, 无论两个分运动的方向是否垂直, 都可以在分运动中应用动能定理, 只是称之为“ 动能定理的分量式”不太恰 当     

关于质点组动能定理的有效性

《大学物理》1987年第5期所载漆、杜同志“关于质点组动能定理的应用”一文(以下简称漆文)重申质点组动能定理不适用于“复杂系统”.笔者仍然认为此种提法值得商榷. 首先,有两点应予澄清. 其一,漆文写道:“传热和作功是两种不同的能量传递方式,不能混为一谈.……从击发到发射的全过程,不仅涉及传热,还涉及化学反应,这能量转化问题已不是一个经典力学的问题”.这段话完全正确.但是,动能定理的“职责”本来就限于机械功与机械能的关系,至于一般的能量转化问题已超出了它的“职责”之外.说动能定理不能处理一般的能量转化问题,这并不足以征明动…     

两例看力学中两个定理的使用问题

通过对两个问题的分析, 指导学生正确运用动量定理和动能定理求解“ 连续体”变质量力学问题, 强化 对此类问题中使用动量定理和动能定理的认识     

力做功的求解方法

一个变力做功的问题,求解方法一般不只一种,但大部分运用动能定理、功能原理等方法求解,本文通过一道例题探讨变力做功的另一种解法.     

巧妙一设计，粗验两规律

动量守恒定律和动能定理是高中物理中非常重要的知识点,也是近几年来高考的热点,本人利用身边物品巧妙设计一方案,既粗略地验证了动量守恒定律,又粗略地验证了动能定理.     

关于质点组动能定理的应用问题

《大学物理》刊出一读者来信谈及质点组动能定理的应用.现作一简单说明. 一般说来,对于一定系统,其中的机械运动仍遵守力学规律,这是正确的.另一方面,因不同运动形式总是相互联系的,若所研究系统的行为不可避免地涉及更高级的运动形式,就需用更高级运动形式的理论以更为有效地描述系统的行为.总的是这样,对具体问题又需作具体分析. 如气缸中理想气体作等温膨胀推动活塞,就气体中二分子相互碰撞过程,质点组动能定理成立.但将气体分子和活塞视作一系统,质点组动能定理不成立.这是因为外界向系统传热使系统能量增加.传热和作功是两种不同的能量…     

动能定理应用的几点思考

分析了动能定理不可以分方向运用,以及规范解题中运用动能定理时需要确定选取的参考系.     

关于误用动能定理的讨论

动能定理是中学物理课程中的重要规律之一,也是高考的热点内容,它将状态量的变化与过程量联系起来.应用动能定理解题时,只需考虑始末运动状态,无需关注运动过程中的细节变化,显得简捷与方便,因此深受老师和同学的欢迎.     

是电势差还是电动势

我院使用的上海版大专《物理学》第七章，有三道题值得商量，其中一道如下．长直载有电流，的导线一侧的同一平面上，有一段导线MN，它与直导线的垂直方向成θ角，其尺寸与位置如图所示，当它以平行长直导线方向作匀速率v运动时，MN两点间电势差多大?哪一点电势高?     

要掌握物理量定义的方法

建立物理量的目的是通过该量来表征物质或物体的状态或性质，并通过探求各量之间所表征的全部内容，集中地包含在它的定义式中．因此，掌握物理量定义的方法，对物理教学具有重要意义．     

给牛顿力学戴上相对论协变的光环,弊大于利

指出本刊一篇文章基本思路的不妥之处，简明扼要地阐明了牛顿力学和相对论力学的分界。     

Itô's formula is the chain rule with wick ordering

Non-commutative stochastic integrals are defined using exponential vectors in Fock space. It is shown that the generalisation of Itô's formula is essentially the ordinary chain rule, combined with Wick ordering.     

Holographic Dark Energy Model is Consistent with Pantheon SN Ia Data

We constrain three cosmological models,i.e.,ACDM model, holographic dark energy(HDE) model and R_h = ct model by using the recent Pantheon compilation of type la supernovae(SN la), the direction measurements of Hubble parameter H(z), and the baryon acoustic oscillations(BAO). The spatial curvature is considered in the ACDM model and the HDE model. We show that the HDE model in a spatially flat and HDE dominate universe has the same behavior as Rh = ct model if the characteristic parameter of the HDE model C_0 approaches to infinity. Numerical results show that the ACDM model is the best favoured one among the three models. The HDE model is consistent with observational data, the best fitting value of C_0 is around 0.8, which implies that the Rh = ct model should be modified to be compatible with the present cosmological observational data. Combing all the datasets, we give strict constraint on the Hubble constant,where h_0=0.694 ± 0.020 for the ACDM model and h_0= 0.689 ±0.019 for the HDE model.Our results imply that the tension of Hubble constant between Planck collaborations and Riess et al. has been partially relaxed. The constraint on the spatial curvature is also given,where Ω_(k0) =-0.066 ± 0.165 for the ACDM model andΩ_(k0)=0.029 ± 0.067 for the HDE model.     

Energy Consumption During Nanoparticle Production: How Economic is Dry Synthesis?

The production of oxide nanoparticles by selected wet-chemistry or dry processes is compared in terms of energy requirements. Clear differences arise for production using electricity-intensive plasma processes, organic- or chloride-derived flame synthesis and liquid based precipitation processes. In spite of short process chains and elegant reactor design, many dry methods inherently require vastly bigger energy consumption than the multi-step wet processes. Product composition strongly influences the selection of the preferred method of manufacturing in terms of energy requirement: Metal oxide nanoparticles of light elements with high valency, e.g. titania demand high volumes of organic precursors and traditional processes excel in terms of efficiency. Products with heavier elements, more complex composition and preferably lower valency such as doped ceria, zirconia, and most mixed oxide ceramics may be readily manufactured by recently developed dry processes.     

Itô versus Stratonovich

A survey is given of the facts and fancies concerning the nonlinear Langevin or Itô equation. Actually, it is merely a pre-equation, which becomes an equation when an interpretation rule is added. The rules of Itô and Stratonovich differ, but both are mathematically consistent and therefore equally admissible conventions. The reason why they seem to lead to physical differences is that the Langevin approach used to arrive at the equation involves a tacit assumption. For systems with external noise this assumption can be justified, and it is then clear that the Stratonovich rule applies. Systems with internal noise, however, can only be properly described by a master equation and the Itô-Stratonovich controversy never enters. Afterward one is free to model the resulting fluctuations either with an Itô or a Stratonovich scheme, but that does not lead to any new information.