Section | Item | Definition |
1.1 (a) | 巴黎用英语怎么说Quantity | In S.I. a quantity is reprented by a number ⨯ a unit, (e.g. m = 3.0 kg). |
1.1 (c) | Scalar | A scalar is a quantity that has magnitude only. |
Vector | A vector is a quantity that has magnitude and direction.低碳产品认证 | |
1.1 (d) | Force | A force on a body is a push or a pull acting on the body from some external body. Unit: N |
Newton’s Third Law | If a body A exerts a force on a body B, then B exerts an equal and opposite force on A. | |
1.1 (f) | ∑ F = m a | The mass of a body ⨯ its acceleration is equal to the vector sum of the forces acting on the body. This vector sum is called the resultant force. |
1.1 (h) | Resolving a vector into components in particular directions | This means finding vectors (the so-called components) in the directions, which add together vectorially to make the original vector, and so, together, are equivalent to this vector. |
1.1 (i) | Density of a material | Unit: kg m 3 in which mass and volume apply to any sample of the material. |
1.1 (j) | Moment (or torque) of a force. | The moment (or torque) of a force about a point is defined as the force ⨯ the perpendicular distance from the point to the line of action of the force, i.e. moment = F d. Unit: Nm武汉狼友. [N.B. the unit is not J] |
1.1 (k) | The principle of moments. | For a system to be in equilibrium, sum of anticlockwi moments about a point = sum of clockwi moments about the same point. |
1.1 (l) | Centre of gravity. | The centre of gravity is the single point within a body at which the entire weight of the body may be considered to act |
1.2 (a) | Displacement | The change in position. The displacement of a point B from a point A is the shortest distance from A to B, together with the direction. Unit: m. |
Mean Speed | Mean speed = Unit: ms-1. | |
Instantaneous Speed | instantaneous speed = rate of change of distance Unit: ms-1. | |
Mean Velocity | Mean velocity = Unit: ms-1. | |
Instantaneous Velocity | The velocity of a body is the rate of change of displacement. Unit: ms-1 | |
Mean Acceleration | Mean Acceleration = Unit: ms-2. | |
Instantaneous Acceleration | The instantaneous acceleration of a body is its rate of change of velocity. Unit: ms-2 | |
Section | Item | Definition | |
1.2 (e) | Terminal Velocity | The terminal velocity is the constant, maximum velocity of an object when the resistive forces on it are equal and opposite to the ‘accelerating’ force (e.g. pull of gravity). | |
1.3 (a) | Work | Work done by a force is the product of the magnitude of the force and the distance moved in the direction of the force.( W.D. = Fxcos θ ) Unit: J [= Nm] | |
1.3 (b) | Hooke’s Law | Provided the elastic limit is not exeeded, the extension is directly proportional to the load applied on the object. | |
Spring constant, k | The spring constant is the force per unit extension. Unit: Nm-1. | ||
1.3 (d) | Energy | The ability to do work. Unit: J | |
1.3 (e) | Principle of conrvation of energy | Energy cannot be created or destroyed, only transferred from one form to another. Energy is a scalar. | |
Potential energy | This is energy possd by virtue of position. (e.g. Gravitational PE = mgh). Unit: J | ||
Kinetic energy | Energy due to motion. Unit: J | ||
1.3( h) | Power | The work done per unit time taken. This is the work done per cond, or energy transferred per cond. Unit: watt (W) [= Js-1]. | |
Efficiency of a system | 鲜花寄语Unit: none | ||
1.4 (h) | Electric current, I. | This is the rate of flow of electric charge. I = ∆Q/∆t. Unit: A | |
1.5 (a) | Potential difference (p.d.), V. | The p.d. between two points is the energy converted from electrical potential energy to some other form per coulomb of charge flowing from one point to the other. Unit: volt (V) [= JC-1]. | |
1.5 (c) | Ohm’s Law. | The current flowing through a metal wire at constant temperature is proportional to the p.d. across it. | |
1.5 (d) | Electrical Resistance, R. | The resistance of a conductor is the ratio of p.d. (V) across it to the current (I) in it. R = V / I Unit: ohm (Ω秦王嬴驷) [= VA-1]. | |
1.5 (g) | Resistivity, ρ | The resistance, R, of a metal wire of length L and cross-ctional area A is given by R = ρ L / A, in which ρ,the resistivity, is a constant (at constant temperature) for the material of the wire. Unit: Ωm | |
1.5 (k) | Superconducting transition temperature | The temperature at which a material, when cooled, los all its electrical resistance, and becomes super-conducting. Some materials (e.g. copper) never become superconducting however low the temperature. | |
1.6 (a) | The Law of Conrvation of Charge. | Electric charge cannot be created or destroyed, (though positive and negative charges can neutrali each other). Charge cannot pile up anywhere. | |
1.6 (f) | e.m.f. | f. of a source is the energy converted from some other form (e.g. chemical) to electrical potential energy per coulomb of charge flowing through the source. Unit: V. | |
Section | Item | Definition | |
2.1 (a) | Progressive wave | A pattern of disturbances travelling through a medium and carrying energy with it, involving the particles of the medium oscillating about their equilibrium positions. | |
2.1 (b) | Transver wave | A transver wave is one where the particle oscillations are at right angles to the direction of travel (or propagation) of the wave. | |
Longitudinal wave | A longitudinal wave is one where the particle oscillations are in line with (parallel to) the direction of travel (of propagation) of the wave. | ||
2.1 (d) | Polarid wave | A polarid wave is a transver wave in which particle oscillations occur in only one of the directions at right angles to the direction of wave propagation. | |
Wavelength of a progressive wave(λ) | The wavelength of a progressive wave is the distance between two successive peaks or troughs. 入团申请书Unit: m | ||
Frequency of a wave (ƒ) | The number of circuits or cycles per cond. Unit: hertz | ||
Period T | Time taken for one complete cycle. | ||
speed of a wave | The velocity of a wave is the distance that the wave moves per unit time. | ||
2.1 (g) | Diffraction | Diffraction is the spreading out of waves when they meet obstacles, such as the edges of a slit. | |
2.1 (h) | The principle of superposition. | The principle of superposition states that if waves meet at the same point in the space, the total displacement at any one point is the vector sum of their individual displacements at that point. | |
2.1 (k) | In pha | Waves arriving at a point are said to be in pha if they have the same frequency and are at the same point in their cycles at the same time. [Wave sources are in pha if the waves have the same frequency and are at the same point in their cycles at the same time, as they leave the sources.] | |
Pha difference | Pha difference is the difference in position of 2 points within a cycle of oscillation. It is measured as a fraction of the cycle or as an angle, where one whole cycle is 2π or 360] | ||
Coherence | Waves or wave sources, which have a constant pha difference between them (and therefore must have the same frequency) are said to be coherent. | ||
2.1 (r) | Stationary (or standing) wave | A stationary wave is a pattern of disturbances in a medium, in which energy is not propagated. The amplitude of particle oscillations is zero at equally-spaced nodes, rising to maxima at antinodes, midway between the nodes. | |
2.2 (a) | Snell’s law | At the boundary between any two given materials, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant. | |
Section | Item | Definition |
2.2 (b) | Refractive Index | For light, Snell's Law may be written: in which 1 and 2 are angles to the normal for light passing between medium 1 and medium 2; n1 and n2 are called the refractive indices of medium 1 and medium 2 respectively. The refractive index of a vacuum is fixed by convention as exactly 1. For air, n = 1.000 |
2.2 (d) | Critical angle | When light approaches the boundary between two media from the 'slower' medium, the critical angle is the largest angle of incidence for which refraction can occur. The refracted wave is then travelling at 90° to the normal. |
2.3 (a) | Photoelectric effect | When light or ultraviolet radiation of short enough wavelength falls on a surface, electrons are emitted from the surface. |
2.3 (d) | Work function | The work function of a surface is the minimum energy needed to remove an electron from the surface. Unit: J |
2.4 (a) | Atomic mass number, A [nucleon number] | The atomic mass number of an atom is the number of nucleons (number of protons + number of neutrons) in its nucleus. led手电 |
Atomic number, Z [proton number] | The atomic number of an atom is the number of protons in its nucleus. [This determines the chemical element which the atom reprents.] | |
Nuclide | 粗腿A nuclide is a particular variety of nucleus, that is a nucleus with a particular A and Z. | |
Isotope | Isotopes are atoms with the same number of protons, but different numbers of neutrons in their nuclei. | |
2.4 (b) | Lepton | The leptons are electrons and electron-neutrinos [and analogous pairs of particles of the so-called cond and third generations]. |
2.4 (e) | Hadron | Hadrons are particles consisting of quarks or antiquarks bound together. Only hadrons (and quarks or antiquarks themlves) can ‘feel’ the strong force. |
Baryon | A baryon is a hadron consisting of 3 quarks or 3 antiquarks. The best known baryons are the nucleons, that is the proton and the neutron. | |
Meson | A meson is a hadron consisting of a quark-antiquark pair. | |
2.5 (b) | Black body | A black body is a body (or surface) which absorbs all the electromagnetic radiation that falls upon it. No body is a better emitter of radiation at any wavelength than a black body at the same temperature. |
Section | Item | Definition | |
Absolute or kelvin temperature | The temperature, T in kelvin (K) is related to the temperature, θ, in celsius (°C) by: T /K= θ /°C + 273.15 . At 0 K (-273.15°C) the energy of particles in a body is the lowest it can possibly be. | ||
Section | Item | Definition |
4.2(a) | Momentum | The momentum of an object is its mass multiplied by its velocity. (p = mv). It is a vector. UNIT: kg m s-1 |
4.2(b) | Newton’s laws of motion: 1st law | An object continues moving at constant speed in a straight line, or remains at rest, unless acted upon by a resultant force. |
Newton’s laws of motion: 2nd law | The rate of change of momentum of an object is proportional to the resultant force acting on it, and takes place in the direction of that force. | |
Newton’s laws of motion: 3rd law | If a body A exerts a force on a body B, then B exerts an equal and opposite force on A. | |
4.2(c) | The principle of conrvation of momentum | The vector sum of the momenta of bodies in a system stays constant even if forces act between the bodies, provided there are no external forces applied on the system. |
Elastic collision. | A collision in which there is no change in total kinetic energy. | |
Inelastic collision. | A collision in which kinetic energy is lost. | |
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