ALevel物理Moment、Material和Wave的重要概念！

　　ALevel考试科目众多，ALevel物理就是其中比较常见的科目，很多考生在选课的时候都会选择物理，不过物理考试考察知识面很广，题目难度往往很大，今天我们来总结一下Moment、Material和Wave这三部分的重要概念！

　　Moment

　　1•Moment – Force multiplied by perpendicular distance between force and the pivot

　　2• Principle of moments – States that for an object to be in equilibrium the sun of the anticlockwise moments equals the sum of the anticlockwise moments (no turning moment)

　　3• An Object is in equilibrium if:

　　Sum of anticlockwise moments = sum of clockwise moments

　　All vertical forces cancel and all horizontal forces cancel

　　4• A Couple – A pair of opposite and equal forces separated by distance d, acting about point p, the turning effect at point p is equal to one of Forces multiplies by the perpendicular distance between the forces

　　5• Centre of mass – Where all of an objects mass appears to act about and moments cancel

　　Materials

　　6• A Newton – Force required to accelerate 1kg by 1ms-2

　　7• A Joule – Work done 1N through a distance of 1m in direction of force

　　8• Law of conservation of energy – energy is never created or destroyed just converted between different types

　　9• Hooke’s Law – The extension of a spring is proportional to the force applied to it as long as the limit of proportionality is not exceeded

　　10• Stress – Force per unit area • Strain – Ratio of extension to original length

　　11• Young’s Modulus – Stiffness constant of a material

　　Waves

　　12• A longitudinal Wave – a propagating wave with oscillations in the same direction as propagation/energy transfer

　　13• A transverse wave – A propagating wave with oscillations perpendicular to the direction of propagation

　　14• Transverse waves can be polarized but longitudinal waves cannot

　　15• Stationary wave – Formed when 2 waves of similar frequency travelling in opposite directions interfere and the resultant wave is the vector sum of each waves displacements at that point by the principle of superposition

　　16• Diffraction – Spreading out of a wave when passed through a slit of around an obstacle

　　17• Coherent Sources – Same frequency and constant phase relationship

　　18• Constructive Interference occurs – 2 waves intersect and interfere through principle of superposition and the resultant displacement.

　　The vector sum of the 2 waves displacement at that point and the phase difference between the 2 waves at that point is a whole number of wavelengths (destructive when 180 degrees phase difference – half number of wavelengths)

　　19• Differences between single and double slit diffraction –

　　Single – Wide central maxima 2x width of others and reduction in intensity going away

　　Double – Same intensity same width going out

　　关于ALevel物理Moment、Material和Wave这三部分的重要概念就为大家介绍到这里了，希望大家能够好好复习，提高备考能力，并且小编建议大家要重视真题训练，这样才能顺利通过考试，如果还想了解更多自学alevel成绩、alevel基础数学词汇等信息，可以在线咨询我们或添加客服微信kewo11！