普朗特(Prandtl)的边界层概念解决了什么流体难题？
What fluid problem did Prandtl's boundary-layer concept solve?
早先用理想无黏流理论算不出物面附近的阻力，普朗特在 1904 年提出边界层：贴近壁面很薄一层黏性主导、速度从零渐增到主流。这把黏性影响局限在薄层内，使外流可用势流求解，奠定了现代空气动力学。
Ideal inviscid theory could not predict drag near surfaces; Prandtl proposed in 1904 a thin boundary layer where viscosity dominates and velocity rises from zero to the freestream. Confining viscosity to that layer lets the outer flow be treated as potential flow, founding modern aerodynamics.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-03 · 2 条独立证据
来源 · Source
Prandtl《论极小摩擦下的流体运动》(Über Flüssigkeitsbewegung bei sehr kleiner Reibung, 第三届国际数学家大会, 1904)；Anderson《空气动力学基础》(Fundamentals of Aerodynamics)
Prandtl, 'Über Flüssigkeitsbewegung bei sehr kleiner Reibung' ('On fluid motion with very small friction', 3rd International Congress of Mathematicians, 1904); Anderson, 'Fundamentals of Aerodynamics'
独立核验依据 · Independent verification: 核验依据 1 ISBN 9787516504413（豆瓣书目条目: 空气动力学基础）；本条出处含多部著作，此标识只担保上面点名 · 核验依据 2 OPENLIBRARY 标识 /works/OL20903326W：Fundamentals of aerody
#边界层 #普朗特 #黏性 #空气动力学
涡轮增压器是怎样回收排气能量来提升发动机功率的？
How does a turbocharger recover exhaust energy to boost engine power?
废气推动涡轮旋转，涡轮同轴带动压气机把更多空气压入气缸，使每循环能喷更多燃料、输出更大功率。它本质上是用排气中的废热和动能驱动一台小型燃气轮机。
Exhaust gas spins a turbine, which on the same shaft drives a compressor that forces more air into the cylinders, allowing more fuel per cycle and more power. It is essentially a small gas turbine driven by the waste heat and kinetic energy of the exhaust.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Watson 与 Janota《内燃机涡轮增压》(Turbocharging the IC Engine)；Heywood《内燃机基础》
Watson & Janota, 'Turbocharging the Internal Combustion Engine'; Heywood, 'Internal Combustion Engine Fundamentals'
独立核验依据 · Independent verification: 核验依据 1 ISBN 9781260116106 (2018)
#涡轮增压 #废气能量 #压气机 #燃气轮机
什么是疲劳破坏，工程上如何预防？
What is fatigue failure and how is it prevented in engineering?
疲劳破坏是指材料在远低于其静强度的反复交变应力下，经过许多循环后突然断裂的现象。工程上通过优化几何形状避免应力集中、表面强化处理、限制工作应力以及定期无损检测来预防疲劳失效。
Fatigue failure is the sudden fracture of a material under repeated cyclic stresses far below its static strength, after many load cycles. Engineers prevent it by avoiding stress concentrations through geometry, surface hardening, limiting operating stress, and performing periodic non-destructive inspection.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
濮良贵 陈国定 吴立言 主编,《机械设计》第10版,高等教育出版社,2019
Piao Lianggui, Chen Guoding and Wu Liyan eds., Machine Design, 10th ed., Higher Education Press, 2019
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040514216（豆瓣书目条目: 机械设计）
#疲劳 #断裂 #可靠性
收缩—扩张喷管（拉瓦尔喷管）为什么能让气流加速到超音速？
Why does a converging–diverging (de Laval) nozzle accelerate flow to supersonic speeds?
在喉部之前气流为亚音速，收缩使其加速至音速；喉部之后截面扩张，根据可压缩流特性，超音速流在扩张段继续加速，从而把热能高效转化为动能，用于火箭和涡轮机。
Upstream of the throat the subsonic flow speeds up to Mach 1 at the throat; downstream the diverging section accelerates the supersonic flow further, converting heat to kinetic energy in rockets and turbines.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
White，《流体力学》（第8版）
White, 'Fluid Mechanics' (8th ed.)
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL1911850W：Fluid mechanics（首版 1979
#喷管 #超音速 #马赫数
什么是“屈服强度”和“极限抗拉强度”？如何从应力—应变曲线得到它们？
What are yield strength and ultimate tensile strength, and how are they obtained from a stress-strain curve?
屈服强度是材料开始发生塑性变形时的应力，对无明显屈服平台的金属常取0.2%残余应变偏移法确定。极限抗拉强度是拉伸曲线上最大工程应力，出现在颈缩之前；二者均由单轴拉伸试验得到。
Yield strength is the stress at which a material begins plastic deformation; for metals without a clear yield point it is found by the 0.2% offset method. Ultimate tensile strength is the maximum engineering stress on the tensile curve before necking; both come from a uniaxial tensile test.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-10-03 · 3 条独立证据
来源 · Source
美国材料与试验协会（ASTM）ASTM E8/E8M《金属材料拉伸试验方法》；Callister《材料科学与工程导论》
ASTM International ASTM E8/E8M 'Standard Test Methods for Tension Testing of Metallic Materials'; Callister, 'Materials Science and Engineering: An Introduction'
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-1-119-45520-2 (Global Ed.) / 978-1-119-45391-8 · 核验依据 2 ISBN 9781292247137 · 核验依据 3 ISBN 9781641950565 (2019)
#屈服强度 #极限抗拉强度 #应力应变曲线 #0.2%偏移
直列四缸发动机为什么天生存在二阶往复惯性力，需要平衡轴来抵消？
Why does an inline four-cylinder engine inherently produce second-order reciprocating forces that need balance shafts?
活塞运动不是纯简谐：由于连杆长度有限，其加速度可展开为频率等于曲轴转速的一阶项，加上频率为两倍转速的二阶项，二阶项幅值大致按曲柄半径与连杆长度之比缩放。直列四缸相邻曲拐相位相差一百八十度，一阶惯性力互相抵消，但四个活塞的二阶分量同相叠加，形成沿气缸轴线、频率为转速两倍的合力，曲轴配重无法消除。因此排量较大的四缸机常加两根以两倍转速反向旋转的 Lanchester 平衡轴，用偏心质量抵消这一激励，代价是增加零件、摩擦与成本；直列六缸和水平对置布局则从相位上天然抵消该项。
Piston motion is not purely sinusoidal: because the connecting rod has finite length, acceleration expands into a first-order term at crank speed plus a second-order term at twice crank speed whose amplitude scales roughly with the ratio of crank radius to rod length. In an inline four the crank throws are 180 degrees apart so first-order forces cancel, but all four second-order components act in phase and sum into a net force along the cylinder axis at twice engine speed, which crankshaft counterweights cannot remove. Larger four-cylinder engines therefore add two Lanchester balance shafts counter-rotating at twice crank speed whose eccentric masses oppose that excitation, at the cost of extra parts, friction and money, while inline sixes and flat layouts cancel the term by phasing alone.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-02
来源 · Source
Taylor，《The Internal-Combustion Engine in Theory and Practice, Vol. 2》（MIT Press）
Taylor, 'The Internal-Combustion Engine in Theory and Practice, Vol. 2' (MIT Press)
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL9251103W：The internal-combustion
#往复惯性力 #二阶不平衡 #Lanchester平衡轴
什么是有限元分析（FEA），它在机械设计中如何应用？
What is finite element analysis (FEA) and how is it applied in mechanical design?
有限元分析是一种把复杂结构离散成许多小单元、再用数值方法求解应力应变分布的工程计算方法。设计者用它来预测零件在载荷下的变形、强度和疲劳寿命，从而在没有实物样机前就优化结构。
Finite element analysis is a computational method that discretizes a complex structure into many small elements and solves for stress and strain distributions numerically. Designers use it to predict deformation, strength, and fatigue life under loads, optimizing structures before building physical prototypes.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
濮良贵 陈国定 吴立言 主编,《机械设计》第10版,高等教育出版社,2019
Piao Lianggui, Chen Guoding and Wu Liyan eds., Machine Design, 10th ed., Higher Education Press, 2019
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040514216（豆瓣书目条目: 机械设计）
#有限元 #数值分析 #结构设计
几何公差（GD&T）与普通尺寸公差有何区别？位置度和最大实体原则有什么用？
How does geometric dimensioning and tolerancing (GD&T) differ from ordinary size tolerances, and what are position tolerance and the maximum material principle used for?
尺寸公差只约束孔轴等要素的大小，几何公差则用公差框格控制形状、方向、位置和跳动，比如平面度、垂直度、位置度，能更明确地表达装配功能要求。位置度以理论正确尺寸定位基准，允许公差带为一个圆柱区，轴或孔在该圆柱内即合格。最大实体原则（MMC）在要素处于最大实体状态时给最小公差，尺寸偏离时公差随之放大，既保证装配不干涉，又放宽加工成本。
Size tolerances only bound features such as hole or shaft diameter, whereas GD&T uses feature control frames to limit form, orientation, location and runout, for example flatness, perpendicularity and position, expressing assembly requirements precisely. Position tolerance locates a feature with basic dimensions and allows a cylindrical tolerance zone the axis must lie in. The maximum material condition (MMC) gives the tightest tolerance when the feature is at its largest material size and enlarges the zone as size departs, guaranteeing assembly without interference while relaxing machining cost.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-02
来源 · Source
Shigley，《机械工程设计》（第10版）
Shigley, 'Mechanical Engineering Design' (10th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9787111104735（豆瓣书目条目: 机械工程设计）
#GD&T #几何公差 #位置度
什么是“应力集中”？为什么在孔、缺口和台阶处特别容易发生？
What is stress concentration, and why does it especially occur at holes, notches, and steps?
应力集中是指构件几何不连续处（如孔、缺口、台阶、圆角）局部应力显著高于名义应力，因为力线在此拥挤。其程度用理论应力集中系数 K_t 量化，疲劳裂纹往往从这些高应力点萌生。
Stress concentration is the local elevation of stress around geometric discontinuities such as holes, notches, fillets, and steps, where stress flow lines crowd together. It is quantified by the theoretical stress concentration factor K_t, and fatigue cracks often initiate at these high-stress points.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-02
来源 · Source
《Peterson 应力集中系数手册》；Shigley《机械工程设计》
Pilkey, 'Peterson's Stress Concentration Factors'; Shigley, 'Mechanical Engineering Design'
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL3283174W：Peterson's stress conce
#应力集中 #应力集中系数 #疲劳 #缺口敏感
什么是基孔制与基轴制？配合分为哪几类？为什么轴比孔易加工时优先采用基孔制？
What are hole-basis and shaft-basis systems, what classes of fit exist, and why is hole-basis preferred when the shaft is easier to machine?
基孔制以基准孔H为基准，改变轴的公差带位置得到不同配合；基轴制以基准轴h为基准，改变孔的公差带。配合按间隙分为三类：间隙配合（恒有间隙，可相对运动）、过盈配合（恒有过盈，靠变形传递力）、过渡配合（可能间隙可能过盈，用于定位）。孔一般用铰刀、镗刀等定尺寸刀具加工，改变孔径要换刀，而轴由车刀调整即可，所以优先固定孔、调整轴，这就是基孔制更常用的原因。
In the hole-basis system the basic hole H is fixed and shaft tolerance zones are varied to create different fits; the shaft-basis system fixes the basic shaft h and varies the hole. Fits divide into three classes by clearance: clearance fits (always a gap, allowing relative motion), interference fits (always tight, transmitting load by deformation) and transition fits (either, used for location). Holes are usually made with fixed-size tools such as reamers or boring bars, changing hole size means changing tooling, while the shaft is sized simply by adjusting the lathe tool, so it is cheaper to hold the hole and vary the shaft, which is why the hole-basis system dominates.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-02
来源 · Source
国际标准化组织（ISO 286）
ISO 286 (ISO system of limits and fits)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9787502623746（豆瓣书目条目: 国际标准化组织ISO）
#公差与配合 #基孔制 #过盈配合
焊缝中的气孔和夹渣是如何形成的？焊接热裂纹又是什么机制？
How do porosity and slag inclusions form in welds, and what mechanism causes hot cracking?
气孔源于熔池中溶解的气体（氢、氮或一氧化碳）在快速凝固时来不及逸出而被困在焊缝中，氢的主要来源是水分和油污，因此焊前清理和干燥极为重要。夹渣是熔渣未充分浮出或前道焊渣未清净被夹在焊道之间，多因焊接速度过快、电流过小或坡口清理不彻底。热裂纹发生在凝固末期，因晶界存在低熔点共晶（如硫磷偏析物），在收缩应力下沿晶界开裂，与硫磷含量和接头拘束度密切相关。
Porosity forms when dissolved gases in the pool (hydrogen, nitrogen or carbon monoxide) are trapped as the weld metal solidifies quickly; hydrogen comes mainly from moisture and oil, so pre-cleaning and drying matter greatly. Slag inclusions result when slag fails to float out or previous weld slag is not fully removed and gets trapped between passes, typically from excessive speed, low current or poor groove cleaning. Hot cracking occurs at the end of solidification when low-melting-point eutectics (e.g. sulphur and phosphorus segregates) along grain boundaries tear under shrinkage stress; it is closely tied to S and P content and joint restraint.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-10-03
来源 · Source
Kalpakjian & Schmid《制造工程与技术》；Groover《现代制造基础》；AWS 美国焊接学会标准
Kalpakjian & Schmid, Manufacturing Engineering and Technology; Groover, Fundamentals of Modern Manufacturing; AWS standards
独立核验依据 · Independent verification: 核验依据 1 ISBN 9789810694067 (7th SI Edition, (c)2014)
#焊接缺陷 #气孔 #热裂纹
滚动轴承为什么比滑动轴承摩擦小，其接触应力又为何极高？
Why do rolling bearings have lower friction, yet very high contact stress?
滚动轴承用滚珠或滚子把轴与座圈之间的滑动变为滚动，摩擦系数因此远低于滑动轴承。但载荷集中在极小的赫兹接触椭圆上，接触应力可达 GPa 量级，所以材料和几何精度要求极高。
Rolling bearings replace sliding between shaft and race with rolling via balls or rollers, giving a much lower friction coefficient than plain bearings. Yet the load concentrates on a tiny Hertzian contact patch, producing gigapascal-level stress, so material and geometry must be precise.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
濮良贵 陈国定 吴立言 主编,《机械设计》第10版,高等教育出版社,2019
Piao Lianggui, Chen Guoding and Wu Liyan eds., Machine Design, 10th ed., Higher Education Press, 2019
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040514216（豆瓣书目条目: 机械设计）
#滚动轴承 #赫兹接触 #摩擦系数 #接触应力
为什么金属零件会在远低于屈服强度的应力下突然断裂，这就是疲劳？
Why do metal parts fail suddenly below their yield strength—is that fatigue?
疲劳指材料在循环载荷下，表面微裂纹萌生并逐步扩展，最终在远低于静强度时断裂。工程中用 S-N 曲线描述应力幅与寿命的关系，因此关键承力件都要按疲劳极限而非静强度来设计。
Fatigue is failure under cyclic loading where surface microcracks initiate and grow until the part breaks well below its static strength. Engineers use S-N curves relating stress amplitude to life, so critical parts are designed to a fatigue limit rather than static strength.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
Suresh《材料疲劳》(Fatigue of Materials)，第 2 版；Schijve《疲劳损伤机理》(Fatigue of Structures and Materials)
Suresh, 'Fatigue of Materials' (2nd ed.); Schijve, 'Fatigue of Structures and Materials'
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL8362230W：Fatigue of Structures a
#疲劳 #S-N曲线 #裂纹扩展 #循环载荷
秸秆全覆盖条件下,免耕播种机依靠哪些工作部件保证种子与土壤紧密接触?
Which working components let a no-till seeder place seed in firm contact with soil beneath a full cover of crop residue?
波纹切茬盘先切断表层残茬并开出窄缝,双圆盘开沟器随后在未翻动的湿土中开出V形种沟,排种器将种子定量投到沟底。带设定下压力的V形镇压轮把沟壁湿土挤向种子实现种土密接并减少水分散失,液压或弹簧仿形机构则维持播深随地表起伏基本不变。
A fluted coulter first slices through surface residue and slits the stubble, double-disc openers then cut a narrow V-furrow in undisturbed moist soil, and the metering unit delivers seed precisely to its base. Downforce-loaded V-shaped press wheels squeeze the wet furrow walls against the seed for firm contact with limited moisture loss, while hydraulic or spring parallelogram linkages keep depth essentially constant over uneven ground.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 来源待核验 · Source pending review
来源 · Source
出处备注：著录含书名，但缺版次 / 出版社 / 年份中的一部分，需编辑补全后才能做独立比对。
C. J. Baker 与 K. E. Saxton《No-Tillage Seeding in Conservation Farming》(Nottingham大学出版社)
C. J. Baker, K. E. Saxton & W. R. Ritchie, No-Tillage Seeding in Conservation Farming, Nottingham University Press
#免耕播种 #镇压轮
设计一台口径300mm的反射式天文望远镜主镜支撑结构时，为什么常采用18点或27点的Whifflettree（浮动支承）而不是简单的三点支承？请从镜面面形误差的角度说明。
When designing the primary-mirror support for a 300 mm reflecting astronomical telescope, why is an 18- or 27-point Whifflettree (floating support) preferred over a simple three-point mount? Explain in terms of mirror figure errors.
重力作用下，三点支承会在镜面内产生较大的弯曲应力，使镜面偏离理想抛物面，引入以三重对称(trefoil)形变和像散为主的低阶像差，且该误差随镜筒指向变化、无法靠重新调焦消除。多点浮动支承把镜子自重分配到更多接触点上，单点载荷下降，面形RMS误差随支承点数近似按幂律降低。对300mm口径、厚径比约1:6的常用镜坯，18点支承通常能把重力面形误差压到衍射极限对应的λ/20 RMS以内。
Under gravity loading, a three-point support induces significant bending stress within the mirror blank, deforming it away from the ideal paraboloid and introducing low-order aberrations dominated by trefoil (threefold-symmetric) deformation and astigmatism — errors that vary with tube pointing and cannot be removed by refocusing. A multi-point floating support distributes the mirror's weight over many contact points, reducing the load per point; figure RMS error falls roughly as a power law with support count. For a 300 mm blank with a typical 1:6 thickness-to-diameter ratio, 18-point support usually holds gravity-induced figure error below λ/20 RMS, matching the diffraction limit.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-04
来源 · Source
Wilson,《Reflecting Telescope Optics II》(Springer, 1999) 第3章 镜面支承；PLOP 镜面支承有限元文档（David Lewis 等）
R.N. Wilson, Reflecting Telescope Optics II (Springer, 1999), Ch.3 Mirror Supports; PLOP mirror-cell FEA documentation (D. Lewis et al.)
独立核验依据 · Independent verification: 核验依据 1 Crossref DOI 10.1007/978-3-662-08488-5
#光学仪器设计 #主镜支承与面形误差
卡诺定理对热机效率给出了什么上限？
What upper limit does Carnot's theorem set on heat engine efficiency?
卡诺定理指出，工作在高温热源与低温热源之间的任何热机，其理想最高效率为1减去低温热源温度除以高温热源温度（温度用热力学温标）。实际热机因摩擦和不可逆损失永远达不到这一上限。
Carnot's theorem says the maximum possible efficiency of any engine between hot reservoir T_h and cold T_c is 1 − T_c/T_h in kelvin. Real engines fall short due to friction and irreversibilities.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-10-04 · 3 条独立证据
来源 · Source
Carnot《论火的动力》(1824)；Cengel 与 Boles《工程热力学》
Carnot, 'Reflections on the Motive Power of Fire' (1824); Cengel & Boles, 'Thermodynamics: An Engineering Approach'
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-1-259-27989-8 (9th ed., McGraw-Hill) · 核验依据 2 ISBN 9781260116106 (2018) · 核验依据 3 ISBN 9780665590955 (2002)
#卡诺 #热机 #效率
四冲程汽油机的一个工作循环包含哪几个冲程？
What strokes make up the four-stroke gasoline engine cycle?
它按进气、压缩、做功（点火膨胀）、排气四个冲程循环，曲轴转两圈完成一次做功。其热效率理论上受奥托循环上限约束，实际还受燃烧、摩擦和泵气损失限制。
It cycles through intake, compression, power (combustion and expansion), and exhaust, with the crankshaft turning twice per power stroke. Its efficiency is bounded in theory by the Otto cycle and in practice by combustion, friction, and pumping losses.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04 · 3 条独立证据
来源 · Source
Heywood《内燃机基础》(Internal Combustion Engine Fundamentals)；Cengel 与 Boles《工程热力学》
Heywood, 'Internal Combustion Engine Fundamentals'; Cengel & Boles, 'Thermodynamics: An Engineering Approach'
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-1-259-27989-8 (9th ed., McGraw-Hill) · 核验依据 2 ISBN 9781260116106 (2018) · 核验依据 3 ISBN 9780665590955 (2002)
#四冲程 #奥托循环 #点火 #热效率
涡轮机是怎样把流体能量变成旋转的？
How does a turbine convert fluid energy into rotation?
涡轮机让高速气体或水流冲击叶片，推动转轮旋转，再把旋转传给发电机或泵。蒸汽、燃气和水轮机都靠这一原理把热或水能转化为机械能。
A turbine lets high-speed steam, gas, or water strike blades that spin a rotor, which drives a generator or pump. Steam, gas, and hydro turbines all turn thermal or hydraulic energy into mechanical work.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04 · 3 条独立证据
来源 · Source
Cengel，《工程热力学：一种工程方法》（第9版）
Cengel, 'Thermodynamics: An Engineering Approach' (9th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-1-259-27989-8 (9th ed., McGraw-Hill) · 核验依据 2 ISBN 9781260116106 (2018) · 核验依据 3 ISBN 9780665590955 (2002)
#涡轮 #叶片 #发电
什么是雷诺数？它如何用来区分层流和湍流？
What is the Reynolds number, and how does it distinguish laminar from turbulent flow?
雷诺数 Re = ρVD/μ，是惯性力与黏性力的比值，是无量纲数。圆管流动中 Re < 约2300 为层流，Re > 约4000 为湍流，中间为过渡区。它可预测流态并用于相似放大。
The Reynolds number Re = ρVD/μ is the ratio of inertial to viscous forces and is dimensionless. For pipe flow, Re < about 2300 is laminar, Re > about 4000 is turbulent, and between them is transitional. It predicts flow regime and enables scaling.
难度 进阶 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
F.M. White《流体力学》；O. 雷诺 1883 年经典实验
F.M. White, 'Fluid Mechanics'; O. Reynolds, classic 1883 pipe-flow experiment
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL1911850W：Fluid mechanics（首版 1979
#雷诺数 #层流 #湍流 #无量纲数
机械图纸上的『公差』是什么，为什么重要？
What is 'tolerance' on a mechanical drawing, and why does it matter?
公差是零件实际尺寸允许偏离设计值的上限范围。合理公差保证零件可互换装配、运转顺畅且成本可控；过严会贵，过松会松旷或卡死。
Tolerance is the allowed deviation from a designed dimension. Good tolerances ensure interchangeable, smoothly running parts at reasonable cost; too tight is expensive, too loose causes play or jamming.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
濮良贵 陈国定 吴立言 主编,《机械设计》第10版,高等教育出版社,2019
Piao Lianggui, Chen Guoding and Wu Liyan eds., Machine Design, 10th ed., Higher Education Press, 2019
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040514216（豆瓣书目条目: 机械设计）
#公差 #配合 #互换性
什么是轴承？它为什么重要？
What is a bearing and why is it important?
轴承是支撑旋转轴并减少其运动摩擦的机械部件，常见类型有滚动轴承和滑动轴承。它能使机器运转更顺畅、更省能，并延长轴和轮子的寿命。
A bearing is a machine element that supports a rotating shaft and reduces friction in its motion, with rolling and sliding bearings being common types. Bearings let machines run smoother, save energy, and extend the life of shafts and wheels.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
濮良贵 陈国定 吴立言 主编,《机械设计》第10版,高等教育出版社,2019
Piao Lianggui, Chen Guoding and Wu Liyan eds., Machine Design, 10th ed., Higher Education Press, 2019
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040514216（豆瓣书目条目: 机械设计）
#轴承 #旋转 #减摩
什么是卡诺循环？它对发动机效率有什么意义？
What is the Carnot cycle and what does it mean for engine efficiency?
卡诺循环是一种理想化的热机循环，由两个等温过程和两个绝热过程组成。它给出了在给定高温和低温热源之间热机可能达到的最高效率上限，真实发动机的效率都低于这个极限。
The Carnot cycle is an idealized heat-engine cycle made of two isothermal and two adiabatic processes. It sets the maximum possible efficiency for any heat engine operating between two given temperature reservoirs, and real engines always fall short of this limit.
难度 进阶 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-10-04 · 3 条独立证据
来源 · Source
Carnot《论火的动力》(1824)；Cengel 与 Boles《工程热力学》
Carnot, 'Reflections on the Motive Power of Fire' (1824); Cengel & Boles, 'Thermodynamics: An Engineering Approach'
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-1-259-27989-8 (9th ed., McGraw-Hill) · 核验依据 2 ISBN 9781260116106 (2018) · 核验依据 3 ISBN 9780665590955 (2002)
#卡诺循环 #热机 #效率
离心泵和容积泵的工作原理有何不同？
How do centrifugal and positive-displacement pumps differ in principle?
离心泵靠高速旋转的叶轮把动能转化为压力，流量随压力变化大，适合大流量低扬程；容积泵靠腔体容积周期性变化挤送液体，压力高、流量稳定，适合高粘度和精密计量。
A centrifugal pump spins an impeller to convert kinetic energy to pressure and varies flow with pressure, suiting high flow. A positive-displacement pump traps and squeezes fluid, giving steady high-pressure flow for viscous or metered duty.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
White，《流体力学》（第8版）
White, 'Fluid Mechanics' (8th ed.)
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL1911850W：Fluid mechanics（首版 1979
#泵 #离心泵 #容积泵
注塑成型的基本过程是什么？为什么制品会出现翘曲变形？
What is the basic injection moulding process, and why do parts warp?
注塑机把塑料颗粒加热熔融，在螺杆推动下高速注入闭合的模具型腔，保压补缩后冷却定型，最后开模顶出制品。翘曲主要源于冷却不均和收缩不均：制品各部位壁厚不同导致冷却速度不同，分子取向和各向异性收缩使内应力不对称释放，从而发生弯曲变形。解决措施包括均匀壁厚设计、优化浇口位置和模具温度场、合理调整保压工艺。
An injection moulding machine melts plastic pellets, injects the melt at high speed into a closed cavity, holds pressure to pack the part, cools until it solidifies, then opens the mould and ejects the product. Warpage comes mainly from uneven cooling and shrinkage: varying wall thickness gives different cooling rates, and molecular orientation plus anisotropic shrinkage releases internal stress asymmetrically, bending the part. Countermeasures include uniform wall design, optimised gate positions and mould temperature fields, and adjusted hold-pressure profiles.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
濮良贵 陈国定 吴立言 主编,《机械设计》第10版,高等教育出版社,2019
Piao Lianggui, Chen Guoding and Wu Liyan eds., Machine Design, 10th ed., Higher Education Press, 2019
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040514216（豆瓣书目条目: 机械设计）
#注塑成型 #翘曲 #模具
为什么锻造能提高金属零件的力学性能？锻造温度范围如何选择？
Why does forging improve the mechanical properties of metal parts, and how is the forging temperature range chosen?
锻造通过压力使金属在固态下塑性变形，打碎铸态的粗大晶粒和枝晶偏析，形成沿变形方向延伸的纤维组织，并消除内部疏松，因此强度和韧性通常高于铸造件。锻造温度范围要选在再结晶温度以上以保证变形能力，又低于过烧温度以防晶界氧化甚至熔化，常用材料都规定了合适的始锻温度和终锻温度。
Forging deforms metal plastically in the solid state, breaking up coarse as-cast grains and dendritic segregation, creating fibre flow aligned with the deformation, and closing internal porosity, so strength and toughness generally exceed those of castings. The forging window sits above the recrystallisation temperature for workability but below the burning temperature where grain boundaries oxidise or melt; standard tables give start and finish forging temperatures for each alloy.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
濮良贵 陈国定 吴立言 主编,《机械设计》第10版,高等教育出版社,2019
Piao Lianggui, Chen Guoding and Wu Liyan eds., Machine Design, 10th ed., Higher Education Press, 2019
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040514216（豆瓣书目条目: 机械设计）
#锻造 #塑性成形 #纤维组织
工程仿真中的有限元分析（FEA）是做什么的？
What does finite element analysis (FEA) do in engineering simulation?
FEA把复杂结构离散成大量小单元，用计算机求解每个单元的受力与变形，再拼成整体响应，从而预测应力、应变和位移，替代或补充昂贵的实体试验。
FEA splits a structure into many small elements and computes each one's force and deformation, assembling them into the whole response to predict stress, strain, and displacement—replacing or supplementing costly tests.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
濮良贵 陈国定 吴立言 主编,《机械设计》第10版,高等教育出版社,2019
Piao Lianggui, Chen Guoding and Wu Liyan eds., Machine Design, 10th ed., Higher Education Press, 2019
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040514216（豆瓣书目条目: 机械设计）
#有限元 #仿真 #应力
什么是齿轮的“模数”？它决定了什么？
What is the module of a gear, and what does it determine?
模数 m = 分度圆直径 / 齿数，单位为 mm，是齿轮齿大小的基准参数。相互啮合的齿轮必须具有相同模数；模数越大，齿越大越厚、承载能力越强。
The module m equals the pitch diameter divided by the number of teeth, in mm, and is the basic measure of tooth size. Meshing gears must share the same module; a larger module gives bigger, stronger teeth and higher load capacity.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 来源待核验 · Source pending review
来源 · Source
出处备注：著录仅给书名，无版次与年份；同一书名常对应多个版次，不臆测具体版本。
美国齿轮制造商协会（AGMA）标准；ISO 6336《齿轮强度计算》
American Gear Manufacturers Association (AGMA) standards; ISO 6336 'Calculation of Load Capacity of Spur Gears'
#齿轮模数 #分度圆 #啮合 #齿数
热力学第一、第二定律分别讲了什么？
What do the first and second laws of thermodynamics state?
第一定律是能量守恒：能量不会凭空产生或消失，只能转化形式。第二定律指出热量自发从高温流向低温，过程伴随熵增，说明有用功有上限、永动机不可能。
The first law is conservation of energy—energy only changes form. The second says heat flows spontaneously from hot to cold with rising entropy, setting a ceiling on useful work and forbidding perpetual motion.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04 · 3 条独立证据
来源 · Source
Y. A. Çengel、M. A. Boles,《Thermodynamics: An Engineering Approach》第8版,McGraw-Hill
Y. A. Cengel & M. A. Boles, Thermodynamics: An Engineering Approach, 8th ed., McGraw-Hill
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-1-259-27989-8 (9th ed., McGraw-Hill) · 核验依据 2 ISBN 9781260116106 (2018) · 核验依据 3 ISBN 9780665590955 (2002)
#热力学 #能量守恒 #熵
精密主轴的滚动轴承为什么要施加预紧，把游隙『消掉』？
Why are the rolling bearings of a precision spindle preloaded to remove internal clearance?
存在游隙时只有承载区的少数滚动体接触，轴在载荷方向会先发生一段几乎无阻力的自由位移，刚度低且载荷方向反转时产生冲击与噪声。轴向预紧（成对角接触球轴承对顶安装、加预紧弹簧或磨配隔套）让所有滚动体始终受载，接触刚度提高、轴心位置确定，从而抑制振动、提高回转精度和系统固有频率。预紧过大则接触应力与摩擦发热上升，温升又因内外圈热膨胀差进一步加大预紧，形成恶性循环并缩短寿命，所以高速主轴多用定压弹簧预紧，并按转速、润滑方式与允许温升折中取值。
With clearance present only a few rolling elements carry load, the shaft can move almost freely for a short distance in the load direction, stiffness is low, and reversals cause impact and noise. Axial preload — back-to-back angular contact ball bearings, springs or ground spacers — keeps every rolling element loaded, raising contact stiffness, fixing the shaft centre and lifting both running accuracy and system natural frequency. Excessive preload raises contact stress and frictional heat, and the temperature difference between inner and outer rings then increases preload further in a runaway loop that shortens life, so high-speed spindles favour constant-pressure spring preload set as a compromise among speed, lubrication and allowable temperature rise.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Harris 与 Kotzalas，《Rolling Bearing Analysis》（第5版）
Harris & Kotzalas, 'Rolling Bearing Analysis' (5th ed.)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780471354574 (2007)
#轴承预紧 #游隙 #主轴刚度
什么是四冲程循环？
What is the four-stroke cycle?
四冲程循环是汽油和柴油内燃机常用的工作循环，包括进气、压缩、做功和排气四个过程。活塞每完成这四个冲程，曲轴转两圈，产生一次动力输出。
The four-stroke cycle is the common operating cycle of gasoline and diesel internal combustion engines, consisting of intake, compression, power, and exhaust strokes. The piston completes these four strokes while the crankshaft turns twice, producing one power output per cycle.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Heywood，《内燃机基础》
Heywood, 'Internal Combustion Engine Fundamentals'
独立核验依据 · Independent verification: 核验依据 1 ISBN 9781260116106 (2018)
#四冲程 #内燃机 #循环
什么是四冲程内燃机？它的四个冲程分别是什么？
What is a four-stroke internal combustion engine, and what are its four strokes?
四冲程内燃机每完成一个工作循环需要活塞往复四个冲程：进气（吸入空气或可燃混合气）、压缩、做功（火花点火或压燃膨胀作功）、排气。曲轴每完成一个循环转两圈，是目前汽车最常用的发动机形式。
A four-stroke engine completes one cycle in four piston strokes: intake (draw in air or mixture), compression, power (combustion expands and does work), and exhaust. The crankshaft turns twice per cycle, and this is the most common automotive engine type.
难度 进阶 · 适合 小学高段(9-12)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
国际汽车工程师学会（SAE International）；J.B. Heywood《内燃机基础》
SAE International; J.B. Heywood, 'Internal Combustion Engine Fundamentals'
独立核验依据 · Independent verification: 核验依据 1 ISBN 9781260116106 (2018)
#四冲程 #内燃机 #奥托循环 #做功冲程
什么是液压系统？
What is a hydraulic system?
液压系统利用密闭液体（通常是油）来传递力和动力，基于帕斯卡原理实现力的放大。叉车、挖掘机和汽车刹车都广泛使用了液压技术。
A hydraulic system uses confined liquid, usually oil, to transmit force and power, amplifying force based on Pascal's principle. Forklifts, excavators, and car brakes all rely heavily on hydraulic technology.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
濮良贵 陈国定 吴立言 主编,《机械设计》第10版,高等教育出版社,2019
Piao Lianggui, Chen Guoding and Wu Liyan eds., Machine Design, 10th ed., Higher Education Press, 2019
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040514216（豆瓣书目条目: 机械设计）
#液压 #帕斯卡原理 #传动
砂型铸造的基本流程是什么？为什么铸件容易出现缩孔缺陷？
What is the basic sand casting process, and why are shrinkage cavities a common casting defect?
砂型铸造先把模型放入型砂制成型腔，合箱后浇入熔融金属，待冷却凝固后落砂取出铸件。金属在凝固时体积收缩，若型腔相应部位缺少液态金属补给，最后凝固的厚大区域就会形成缩孔。为此需要设置冒口储存补缩用金属，并利用浇注温度、冷铁等控制凝固顺序，让缩松尽量转移到冒口中。
In sand casting a pattern forms a cavity in moulding sand, the flask is closed, molten metal is poured in, and after solidification the casting is shaken out. Metals shrink as they solidify; where the cavity cannot be refilled with liquid metal, the last-to-solidify thick sections form shrinkage cavities. Risers store extra liquid to feed the casting, and pouring temperature, chillers and solidification sequencing are used so any porosity ends up in the riser instead of the part.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
濮良贵 陈国定 吴立言 主编,《机械设计》第10版,高等教育出版社,2019
Piao Lianggui, Chen Guoding and Wu Liyan eds., Machine Design, 10th ed., Higher Education Press, 2019
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040514216（豆瓣书目条目: 机械设计）
#铸造 #砂型铸造 #缩孔
杨氏模量(Young's modulus)描述的是材料的什么性质？
What property does Young's modulus describe?
它衡量材料在弹性范围内抵抗拉伸或压缩变形能力的大小，等于正应力与正应变的比值。模量越大，材料越『硬』、越不容易被拉长，是结构选材和设计刚度的基本参数。
It measures a material's resistance to axial deformation within the elastic range, equal to normal stress divided by normal strain. A larger modulus means a 'stiffer' material that is harder to stretch, and it is a basic parameter for material selection and stiffness design.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 来源待核验 · Source pending review
来源 · Source
出处备注：著录仅给书名，无版次与年份；同一书名常对应多个版次，不臆测具体版本。
Beer 与 Johnston《材料力学》(Mechanics of Materials)；Timoshenko《材料强度》(Strength of Materials)
Beer & Johnston, 'Mechanics of Materials'; Timoshenko, 'Strength of Materials'
#杨氏模量 #弹性模量 #应力 #应变
数控机床（CNC）是如何控制刀具按程序运动的？什么是闭环控制？
How does a CNC machine tool move the cutting tool along programmed paths, and what is closed-loop control?
数控系统把零件程序翻译成各轴的位置指令，伺服系统带动工作台或主轴按指令运动，插补器在相邻坐标点之间实时计算中间点，使刀具走出直线、圆弧等轮廓。开环系统只发指令不检测实际位置，精度受步进电机丢步影响；闭环系统用编码器或光栅反馈实际位置并不断修正偏差，定位精度高，是精密加工的主流配置。
A CNC system decodes the part program into axis position commands, servos drive the table or spindle accordingly, and the interpolator computes intermediate points between coordinates in real time so the tool traces lines, arcs and other contours. An open-loop system only sends commands and never checks actual position, so accuracy suffers from stepper motor lost steps; a closed-loop system uses encoders or linear scales to feed actual position back and continuously correct errors, giving high positioning accuracy and is standard in precision machining.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-11-02
来源 · Source
国际标准化组织（ISO 6983，G代码）
ISO 6983 (CNC G-code standard)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9787502623746（豆瓣书目条目: 国际标准化组织ISO）
#数控加工 #CNC #伺服控制
热交换器是如何实现两种流体换热的？
How does a heat exchanger transfer heat between two fluids?
热交换器让两种流体隔着导热壁面流动而不混合，热量从高温侧传到低温侧。常见形式有管壳式、板式等，广泛用于空调、发电和化工。
A heat exchanger lets two fluids flow past a conducting wall without mixing, so heat moves from the hot side to the cold. Shell-and-tube and plate types are common in HVAC, power, and chemical plants.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
Cengel，《传热与传质》（第5版）
Cengel, 'Heat and Mass Transfer' (5th ed.)
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL20333053W：Heat and Mass Transfer
#热交换器 #传热 #管壳式
卡诺定理说明了什么？为什么实际热机效率必然低于卡诺效率？
What does Carnot's theorem state, and why must a real heat engine's efficiency be below the Carnot efficiency?
卡诺定理指出：工作于两个恒温热源之间的任何热机，其效率都不可能超过可逆卡诺热机，即 η_Carnot = 1 − T_c/T_h。实际热机存在摩擦、有限温差传热、非平衡过程等不可逆损失，因此效率必然更低。
Carnot's theorem states that no heat engine operating between two reservoirs can exceed the efficiency of a reversible Carnot engine: η_Carnot = 1 − T_c/T_h. Real engines suffer friction, finite-rate heat transfer, and non-equilibrium losses, so their efficiency is necessarily lower.
难度 进阶 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-02
来源 · Source
Moran & Shapiro《工程热力学基础》；S. Carnot《论火的动力》（1824）
Moran & Shapiro, 'Fundamentals of Engineering Thermodynamics'; S. Carnot, 'Reflections on the Motive Power of Fire' (1824)
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL10501410W：Reflections on the mot
#卡诺定理 #热机效率 #可逆 #热力学第二定律
什么是应力集中，工程上如何避免？
What is stress concentration, and how is it avoided in practice?
在孔、缺口、尖角等几何突变处，局部应力会远高于平均应力，称为应力集中，易成为裂纹起点。工程上用圆角过渡、避免尖角、开卸荷槽等来缓和。
At holes, notches, or sharp corners, local stress far exceeds the average—this is stress concentration, a common crack origin. Designers ease it with fillets, avoiding sharp angles, and relief grooves.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
濮良贵 陈国定 吴立言 主编,《机械设计》第10版,高等教育出版社,2019
Piao Lianggui, Chen Guoding and Wu Liyan eds., Machine Design, 10th ed., Higher Education Press, 2019
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040514216（豆瓣书目条目: 机械设计）
#应力集中 #圆角 #裂纹
六西格玛质量管理中的DMAIC各代表什么？它与传统质量管理有何不同？
What does DMAIC stand for in Six Sigma quality management, and how does it differ from traditional quality control?
DMAIC是定义（Define）、测量（Measure）、分析（Analyze）、改进（Improve）、控制（Control）的首字母，是六西格玛改进项目的数据驱动流程框架。它与传统质量管理的关键区别在于强调用统计方法量化缺陷率、以西格玛水平衡量过程能力，并由跨职能团队围绕顾客关键质量特性系统改进，最终把缺陷率降到百万分之3.4以下的水平。
DMAIC stands for Define, Measure, Analyze, Improve and Control, the data-driven framework of Six Sigma improvement projects. Its key difference from traditional quality control is that defects are quantified statistically, process capability is expressed in sigma levels, and cross-functional teams improve around critical-to-quality customer requirements, ultimately driving defect rates below 3.4 parts per million.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
Six Sigma（Pyzdek & Keller）；ISO 9001；机器视觉检测（Davies《Machine Vision》）
Six Sigma (Pyzdek & Keller); ISO 9001; machine vision inspection (Davies, Machine Vision)
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL3390351W：Machine Vision（首版 1991）
#六西格玛 #DMAIC #质量工程
齿轮的齿廓为什么常做成渐开线形状？
Why are gear tooth profiles usually made involute?
渐开线齿廓能保证两齿轮啮合时传动比恒定，且制造和安装误差的容忍度较好。它在整个啮合过程中压力角基本不变，因此成为最普遍的标准齿形。
An involute profile keeps the gear ratio constant during meshing and tolerates manufacturing and assembly errors well. Its pressure angle stays nearly constant through engagement, making it the dominant standard tooth form.
难度 进阶 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Shigley《机械工程设计》(Mechanical Engineering Design)，第 10 版；Budynas 与 Nisbett《Shigley 机械设计》
Shigley, 'Mechanical Engineering Design' (10th ed.); Budynas & Nisbett, 'Shigley's Mechanical Engineering Design'
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780071077835 (2019)
#渐开线 #齿轮 #传动比 #压力角
雷诺数(Reynolds number)在工程流体里起什么作用？
What role does the Reynolds number play in fluid engineering?
雷诺数是惯性力与黏性力的比值，用来判断流动是层流还是湍流，并作为相似准则把小模型实验推广到真实尺寸。工程师据此选择管径、流速和泵的设计参数。
The Reynolds number is the ratio of inertial to viscous forces and predicts whether flow is laminar or turbulent; as a similarity criterion it lets small-model tests scale to full size. Engineers use it to pick pipe diameter, velocity, and pump parameters.
难度 进阶 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-02
来源 · Source
Munson 等《流体力学基础》(Fundamentals of Fluid Mechanics)；White《黏性流体力学》
Munson et al., 'Fundamentals of Fluid Mechanics'; White, 'Viscous Fluid Flow'
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL2677306W：Fundamentals of fluid m
#雷诺数 #层流 #湍流 #相似准则
为什么轴承能让旋转的机器又省力又耐用？
Why do bearings make rotating machinery smoother and longer-lasting?
轴承把轴与机座之间笨重的滑动摩擦变成滚动摩擦（滚动轴承）或薄油膜内的剪切摩擦（滑动轴承），摩擦系数可下降一个数量级。滚动轴承用滚珠或滚柱在内外圈之间滚动，以点或线接触承载；滑动轴承靠油泵或自吸作用把润滑油楔进间隙，形成动压油膜把轴"托"起来，完全避免金属直接接触。没有轴承，高铁轮对、电机转子很快就会烧毁。
Bearings replace the heavy sliding friction between shaft and housing with rolling friction (rolling bearings) or shear within a thin oil film (sliding bearings), cutting the friction coefficient by an order of magnitude. Rolling bearings use balls or rollers between the inner and outer races and carry load at point or line contacts; sliding bearings wedge lubricant into the clearance to build a hydrodynamic film that floats the shaft, avoiding metal-to-metal contact entirely. Without bearings, a train wheelset or motor rotor would soon burn up.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
濮良贵 陈国定 吴立言 主编,《机械设计》第10版,高等教育出版社,2019
Piao Lianggui, Chen Guoding and Wu Liyan eds., Machine Design, 10th ed., Higher Education Press, 2019
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040514216（豆瓣书目条目: 机械设计）
#轴承 #摩擦 #润滑
汽车减振器（避震器）是怎样把颠簸"吃"掉的？
How does a car shock absorber "eat" the bumps?
减振器本身不支撑车身重量，那是弹簧的工作；它的任务是把振动能量耗散掉。减振器内部是液压缸，活塞上下运动时迫使油液流过小孔和阀片，液体流动的黏性阻力把机械能变成热能散发。弹簧负责储存能量、把冲击变得平缓，减振器负责把弹簧储存的能量逐步"泄"掉，两者配合车身才能很快平稳。伸张与压缩行程的阻尼大小可以不同，以兼顾舒适与操控。
A shock absorber does not carry the car's weight — springs do. Its job is to dissipate vibrational energy. Inside is a hydraulic cylinder: as the piston strokes up and down it forces oil through small orifices and valve discs, and viscous drag converts mechanical energy into heat. The spring stores energy and softens the impact; the damper bleeds that stored energy away, and together they settle the body quickly. Damping can differ between extension and compression strokes to balance comfort and handling.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
濮良贵 陈国定 吴立言 主编,《机械设计》第10版,高等教育出版社,2019
Piao Lianggui, Chen Guoding and Wu Liyan eds., Machine Design, 10th ed., Higher Education Press, 2019
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040514216（豆瓣书目条目: 机械设计）
#减振器 #阻尼 #液压
穿孔板加背后空腔构成的吸声结构为何只在低频窄带内吸声效果突出?
Why does a perforated-panel absorber backed by an air cavity work strongly only over a narrow low-frequency band?
各孔颈内的空气柱与背后空腔组成亥姆霍兹共振系统,当入射声频率接近共振频率时,孔颈处声阻抗与空气特性阻抗匹配,垂直入射吸声系数达到峰值;偏离该频率后法向声抗迅速增大,吸声能力急剧衰减。在空腔内填充多孔材料可引入阻尼展宽有效带宽,但峰值高度相应有所降低。
The air plug in each perforation together with the backing cavity forms a Helmholtz resonator, and near resonance the neck impedance matches the characteristic impedance of air, producing a sharp peak in normal-incidence absorption. Away from that band the normal acoustic reactance grows rapidly and absorption collapses; filling the cavity with porous material adds damping that broadens the useful band at some cost in peak value.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 来源待核验 · Source pending review
来源 · Source
出处备注：著录含书名，但缺版次 / 出版社 / 年份中的一部分，需编辑补全后才能做独立比对。
马大猷主编《噪声与振动控制工程手册》(机械工业出版社)共振吸声结构章节
Ma Dayou (ed.), Handbook of Noise and Vibration Control Engineering, China Machine Press, resonant-absorber section
#亥姆霍兹共振 #吸声系数
联合收割机的脱粒滚筒转速为什么要随作物含水率进行调整，调整不当各会出现什么后果？
Why must a combine harvester operator adjust threshing cylinder speed with crop moisture content, and what goes wrong in either direction?
籽粒潮湿时与穗轴结合牢固，需要更高的滚筒线速度才能脱净，否则未脱净损失迅速上升；籽粒干燥时同样转速会把谷粒打裂甚至脱壳，破碎率超标。实际作业通常在每分钟七百到一千一百转范围内按含水率设定，并联动放宽凹板间隙，用损失率和破碎率两个指标反复校准。
Damp grain clings tightly to the ear and demands a higher peripheral drum speed, otherwise unthreshed losses climb fast, while the same speed cracks dry kernels and pushes breakage beyond grade limits. Crews typically set the cylinder between roughly seven hundred and eleven hundred rpm according to moisture and widen the concave clearance accordingly, tuning the setting against both grain loss and kernel breakage counts.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-11-02
来源 · Source
GB/T 8094《收获机械 联合收割机 技术条件》脱粒性能要求
Srivastava, Goering, Rohrbach & Buckmaster, Engineering Principles of Agricultural Machines, 2nd ed., ASABE, threshing and separation chapters
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL4327342W：Engineering principles
#脱粒滚筒 #作业参数
双层中空玻璃的两片玻璃为什么常常故意做成不同厚度？
Why are the two panes of an insulating glass unit deliberately specified with unequal thicknesses?
若两片玻璃等厚，二者的吻合临界频率重合，隔声曲线在同一频段叠加出一个共同的深谷，计权隔声量被明显拖累。改成不等厚度让两个低谷彼此错开，再辅以较宽的空气腔抑制质量-空气-质量共振，构件便能在更宽的频带内维持平稳的隔声衰减。
Equal-thickness panes share one coincidence frequency, their transmission-loss dips stack into a single deep valley in the same band and drag down the weighted sound reduction index. Unequal thickness staggers those dips, and a wider cavity damps the mass-air-mass resonance, so the assembly holds steady attenuation across a much broader frequency range.
难度 进阶 · 适合 大众
CC BY 4.0 · 来源待核验 · Source pending review
来源 · Source
出处备注：著录仅给书名，无版次与年份；同一书名常对应多个版次，不臆测具体版本。
GB/T 8485《建筑门窗空气声隔声性能分级及检测方法》
ISO 10140-2, Acoustics — Laboratory measurement of sound insulation of building elements, airborne sound insulation
#隔声构造 #吻合效应
设计折射式望远物镜时为何首先消色差,阿贝正弦条件又在其中约束什么?
In designing refracting telescope objectives, why is chromatic aberration corrected first, and what does the Abbe sine condition constrain there?
光学玻璃的色散使不同波长焦点沿轴分离,即便球差已校正,星像仍带彩色晕边,故先用双胶合或三片复消色差结构消除初级位置色差。阿贝正弦条件n·y·sin u=n′·y′·sin u′要求孔径边缘与小视场同时满足等光程成像,从而消除彗差,是望远与显微物镜齐明设计的判据。两者完成后,剩余二级光谱便成为大口径复消色差系统的性能瓶颈。
Optical glass dispersion separates focal points along the axis by wavelength, so star images show colored fringes even after spherical correction; designers therefore cancel primary axial color with doublet or triplet apochromatic layouts first. The Abbe sine condition n·y·sin u=n′·y′·sin u′ demands equal optical path from aperture edge across the small field, eliminating coma and serving as the aplanatism criterion for telescope and microscope objectives. With both satisfied, residual secondary spectrum remains the performance bottleneck of large-aperture apochromatic systems.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Kingslake & Johnson《Lens Design Fundamentals》第2版
Kingslake & Johnson, Lens Design Fundamentals, 2nd ed., SPIE Press
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780124086500 (2024)
#消色差 #正弦条件
轿车过弯时车身为什么会向外侧倾斜？那根横向的防倾杆又是如何抑制侧倾的？
Why does a car body lean outward in a corner, and how does the transverse anti-roll bar suppress that roll?
侧倾源于离心力作用在高于侧倾中心的车身上所形成的翻转力矩。防倾杆是一根横贯左右的U形扭杆弹簧：两轮同向上下跳动时它随之空转、不起作用；一旦左右轮行程出现差异，杆身被扭转并产生反抗侧倾的回复力矩，相当于给车轴附加了侧倾刚度，使车身滚转角减小。前后轴防倾杆刚度的配比还会影响不足转向或过多转向的平衡，是底盘调校的关键参数。
Body roll comes from centrifugal force acting on a centre of gravity located above the roll centres, creating an overturning moment about the suspension. An anti-roll bar is a U-shaped torsion spring spanning the axle: when both wheels bounce together it merely pivots and does nothing, but when their travel differs the bar twists and develops a restoring torque against roll, adding roll stiffness to that axle and shrinking the roll angle. The front-to-rear split of roll stiffness also shifts the car toward understeer or oversteer, making it a key chassis tuning parameter.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Gillespie, T. D.《Fundamentals of Vehicle Dynamics》，SAE International，1992
Gillespie, T. D., Fundamentals of Vehicle Dynamics, SAE International, 1992
独立核验依据 · Independent verification: 核验依据 1 ISBN 9781560911999 (1992)
#侧倾 #防倾杆 #侧倾刚度 #不足转向
职业安全防护中工程控制、管理控制、个人防护的优先顺序是什么？为什么要这样排列？
What is the hierarchy of occupational safety controls, engineering, administrative and personal protective equipment, and why is it ordered this way?
职业危害控制遵循消除或替代、工程控制、管理控制、个人防护装备（PPE）的优先层级：最好从源头消除或替换危害源，其次用通风、隔离、防护罩等工程手段降低危害，再以轮岗、培训等管理措施减少暴露时间，PPE是最后一道防线。顺序的依据是可靠程度：工程控制不依赖人的行为，管理措施依赖制度执行，PPE依赖使用者正确佩戴且随时可能失效，所以越靠前的措施越有效、越应优先落实。
Hazard control follows the hierarchy of elimination or substitution, engineering controls, administrative controls and personal protective equipment: remove or replace the hazard at source first, then reduce it with ventilation, isolation or guards, then limit exposure with rotation and training, with PPE as the last resort. The ordering reflects reliability: engineering controls do not depend on human behaviour, administrative controls depend on discipline, and PPE depends on workers wearing it correctly and can fail at any moment, so the higher a measure sits in the hierarchy, the more effective it is and the higher its priority.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 来源待核验 · Source pending review
来源 · Source
出处备注：本题原挂出处与答案内容不符，已撤回；具体书目待补，暂不展示来源。
本题原挂出处与答案内容不符，已撤回；具体书目待补。
Previous citation withdrawn as unsupported for this answer; a specific source is pending.
#职业安全 #危害控制层级 #个人防护
汽车发动机的一个四冲程循环包含哪四个步骤？
What are the four strokes of a typical four-stroke engine cycle?
依次是进气（吸入空气燃油混合气）、压缩（活塞上行使混合气受压）、做功（火花点燃膨胀推动活塞）、排气（排出废气）。曲轴每两圈完成一个循环，四个步骤各占半圈。
They are intake (draw in air–fuel), compression (squeeze it), power (spark ignites and expansion drives the piston), and exhaust (push out gases). The crankshaft turns twice per cycle.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
Heywood，《内燃机基础》
Heywood, 'Internal Combustion Engine Fundamentals'
独立核验依据 · Independent verification: 核验依据 1 ISBN 9781260116106 (2018)
#内燃机 #四冲程 #循环
什么是摩擦力？
What is friction?
摩擦力是两个接触表面相对运动或试图相对运动时产生的阻力。摩擦既会浪费能量并造成磨损，也能帮助汽车刹车和人们行走。
Friction is the resistance that arises when two surfaces are in contact and move or try to move relative to each other. Friction both wastes energy and causes wear, yet it also enables car braking and human walking.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
濮良贵 陈国定 吴立言 主编,《机械设计》第10版,高等教育出版社,2019
Piao Lianggui, Chen Guoding and Wu Liyan eds., Machine Design, 10th ed., Higher Education Press, 2019
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040514216（豆瓣书目条目: 机械设计）
#摩擦 #力 #接触
发动机和电动机有什么区别？
What is the difference between an engine and a motor?
发动机通常指将燃料燃烧产生的热能转化为机械能的内燃机。电动机则是把电能转化为旋转运动的装置，没有燃烧过程，结构更简单也更安静。
An engine usually refers to an internal combustion engine that converts the heat from burning fuel into mechanical work. A motor, by contrast, converts electrical energy into rotary motion and has no combustion, making it simpler and quieter.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
David Macaulay,《The Way Things Work》,Houghton Mifflin,1988;中译《万物运转的秘密》
D. Macaulay, The Way Things Work, Houghton Mifflin, 1988; Chinese ed.
独立核验依据 · Independent verification: 核验依据 2 OPENLIBRARY 标识 /works/OL15130328W：The Way Things Work（按标
#发动机 #电动机 #能量转换
轴承在机器里起什么作用？
What role do bearings play in machines?
轴承支撑旋转或直线运动部件，把滑动摩擦变为滚动摩擦，显著降低摩擦与磨损，让轴能平稳、低阻力地转动。常见有滚动轴承和滑动轴承两类。
Bearings support rotating or moving parts and turn sliding friction into rolling friction, cutting resistance and wear so shafts spin smoothly. Common types are rolling and sliding bearings.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
濮良贵 陈国定 吴立言 主编,《机械设计》第10版,高等教育出版社,2019
Piao Lianggui, Chen Guoding and Wu Liyan eds., Machine Design, 10th ed., Higher Education Press, 2019
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040514216（豆瓣书目条目: 机械设计）
#轴承 #摩擦 #支撑
齿轮有什么作用？
What is the purpose of gears?
齿轮通过相互啮合的轮齿传递旋转运动和动力。它们可以改变转速、改变转动方向，或者放大或缩小所传递的力矩。
Gears transmit rotational motion and power through interlocking teeth. They can change rotational speed, reverse direction, or increase and decrease the torque delivered.
难度 入门 · 适合 小学低段(6-8)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
濮良贵 陈国定 吴立言 主编,《机械设计》第10版,高等教育出版社,2019
Piao Lianggui, Chen Guoding and Wu Liyan eds., Machine Design, 10th ed., Higher Education Press, 2019
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040514216（豆瓣书目条目: 机械设计）
#齿轮 #传动 #力矩
机油桶上的『5W-30』是什么意思，冬天为什么要选前面数字小的？
What does 5W-30 on a bottle of engine oil mean, and why pick a lower first number for winter?
这是多级粘度标号：W 前的数字对应低温性能，用规定低温下的启动与泵送粘度上限分级，数字越小表示低温流动性越好；后面的数字对应 100 ℃ 时的运动粘度区间以及高温高剪切粘度要求。冷启动时机油若太稠，油泵来不及把油送到轴瓦和凸轮，发动机磨损主要就发生在这几十秒里，所以严寒地区选 0W 或 5W。高温档也不能随意降低，否则油膜太薄承载不了轴承比压；随着行驶里程增加，添加剂耗尽和剪切变稀会让油品跌出等级，这正是需要按里程换油的原因。
It is a multigrade designation: the number before W is a low-temperature class defined by limits on cranking and pumping viscosity at specified cold temperatures, so a smaller number means better cold flow, while the second number sets the kinematic viscosity band at 100 °C plus high-temperature high-shear requirements. On a cold start, oil that is too thick keeps the pump from reaching bearings and cams, and most engine wear happens in those first tens of seconds, which is why 0W or 5W grades suit severe winters. The high-temperature grade cannot simply be lowered either, since a thinner film may not carry bearing pressure, and additive depletion plus shear thinning eventually push used oil out of grade, which is what oil-change intervals address.
难度 入门 · 适合 小学高段(9-12)
CC BY 4.0 · 来源待核验 · Source pending review
来源 · Source
出处备注：著录仅给书名，无版次与年份；同一书名常对应多个版次，不臆测具体版本。
SAE J300《Engine Oil Viscosity Classification》
SAE J300, 'Engine Oil Viscosity Classification'
#机油粘度等级 #SAE J300 #冷启动磨损
什么是简单机械？
What is a simple machine?
简单机械是最基础的力学装置，用来改变力的大小、方向或作用点。常见的六种简单机械包括杠杆、滑轮、斜面、楔子、螺旋和轮轴。
A simple machine is the most basic mechanical device used to change the magnitude, direction, or point of application of a force. The six classical simple machines are the lever, pulley, inclined plane, wedge, screw, and wheel and axle.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
濮良贵 陈国定 吴立言 主编,《机械设计》第10版,高等教育出版社,2019
Piao Lianggui, Chen Guoding and Wu Liyan eds., Machine Design, 10th ed., Higher Education Press, 2019
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040514216（豆瓣书目条目: 机械设计）
#简单机械 #杠杆 #力学
滚动轴承和滑动轴承的主要区别是什么？
What is the main difference between rolling-element bearings and plain (sliding) bearings?
滚动轴承用滚珠或滚子把两接触面隔开，摩擦小、所需润滑剂少、启动力矩低。滑动轴承两表面以流体油膜直接接触滑动（如轴颈轴承），适合高载、高速且要求安静运转的场合。
Rolling-element bearings use balls or rollers to separate the two surfaces, giving low friction and needing little lubricant with low starting torque. Plain bearings have surfaces in sliding contact supported by a fluid film (e.g., journal bearings) and suit high-load, high-speed, quiet-running applications.
难度 入门 · 适合 小学低段(6-8)
CC BY 4.0 · 已核验 · Verified 2026-11-02
来源 · Source
SKF 轴承产品技术手册；Shigley《机械工程设计》
SKF bearing catalogue; Shigley, 'Mechanical Engineering Design'
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL16977151W：Shigley's mechanical e
#滚动轴承 #滑动轴承 #摩擦 #油膜
说机器人有『6个自由度』是什么意思？
What does it mean when a robot is said to have 'six degrees of freedom'?
自由度指物体能独立运动的方向数：三维空间中的刚体可有3个平移和3个转动，共6个。工业机械臂达到6自由度就能让末端到达空间任意位姿。
A degree of freedom is an independent direction of motion; a rigid body in 3D has three translations and three rotations—six total. A 6-DOF arm can place its end at any position and orientation.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
濮良贵 陈国定 吴立言 主编,《机械设计》第10版,高等教育出版社,2019
Piao Lianggui, Chen Guoding and Wu Liyan eds., Machine Design, 10th ed., Higher Education Press, 2019
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040514216（豆瓣书目条目: 机械设计）
#自由度 #机器人 #运动
齿轮的传动比是什么意思？
What does the gear ratio of a pair of gears mean?
传动比是两个啮合齿轮齿数之比，等于它们转速的反比。大齿轮带小齿轮会提速，小齿轮带大齿轮会增力减速，是机械变速与省力的主要手段。
Gear ratio is the ratio of tooth counts, equal to the inverse ratio of speeds. A big gear driving a small one speeds up; a small driving a big one trades speed for torque.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
濮良贵 陈国定 吴立言 主编,《机械设计》第10版,高等教育出版社,2019
Piao Lianggui, Chen Guoding and Wu Liyan eds., Machine Design, 10th ed., Higher Education Press, 2019
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040514216（豆瓣书目条目: 机械设计）
#齿轮 #传动比 #转速