# Physics A2 Level

 Force rate of change of momentum Momentum mass times velocity Newton's laws of motion First law: an object continues at rest or in uniform motion unless it is acted on by a resultant forceSecond law: the rate of change of momentum of an object is proportional to the resultant force on itThird law: when two objects interact, they exert equal and opposite forces on one another Newton's law of gravitation the gravitational force F between two point masses m1 and m2 at distance r apart is given by F=Gm1m2/r2 Impulse force times time for which the force acts on an object Principle of conservation of momentum when two or more bodies interact, the total momentum is unchanged, provided no external forces act on the bodies Conservation of momentum for a system of interacting objects is the total momentum of the objects remains constant provided no external resultant force acts on the system Kinetic energy the energy of a moving object due to its motion Explosion when two objects fly apart, the two objects carry away equal and opposite momentum Elastic collision a collision in which the total kinetic energy after the collision is equal to the kinetic energy before the collision Uniform circular motion motion of an object moving at a constant speed along a circular path Angular displacement the angle an object in circular motion turns through Angular speed the rate of change of angular displacement of an object in circular motion Centripetal acceleration for an object moving at speed v in uniform circular motion its centripetal acceleration a=v2/r towards the centre of the circle Centripetal force the resultant force of an object that moves along a circular path Equilibrium state of an object when at rest or in uniform motion Amplitude the maximum displacement from equilibrium of an oscillating object Displacement distance in a given direction Free oscillations oscillations where there is no damping and no periodic force acting on the system so the amplitude of the oscillation is constant Time period time taken for one complete cycle of oscillations Frequency the number of cycles of oscillation per second Angular frequency for an object oscillating at frequency f in simple harmonic motion its angular frequency = 2pif Phase difference Simple harmonic motion motion of an object if its acceleration is proportional to the displacement of the object from equilibrium and is always directed towards the equilibrium position Dissipative forces forces that transfer energy which is wasted Damped oscillations oscillations that reduce in amplitude due to the presence of resistive forces such as friction and drag1.Lightly damped system: amplitude of oscillations decreases gradually2.Heavily damped system: the system slowly returns to equilibrium without oscillating3.Critically damped system: system returns to equillibrium in the least possible time without oscillating Periodic force a force that varies regulary in magnitude with a definite time period Natural frequency the frequency of free oscillations of an oscillating system Forced oscillations oscillations of a system that is subjected to an external periodic force Resonance the amplitude of vibration of an oscillating system subjected to a periodic force is largest when the periodic force has the same frequency as the resonance frequency of the system Resonant frequency the frequency of an oscillating system in resonance Gravitational field the region surrounding an object in which it exerts a gravitational force on any other object Line of force/ Field line a line followed by a, small mass in a gravitational field/ a small positively charged object in an electric field/ a free north pole in a magnetic field, acted on by no other forces than the force due to the field Radial field a field in which th field lines are straight and converge or diverge as if from a single point Uniform field a region where the field strength is the same in magnitude and direction at every point in the field Gravitational potential the work done per unit mass to move a small object from infinity to that point in a gravitational field Gravitional potential energy the work done to move a small object from infinity to that point in the field Potential gradient at a point in a field is the change of potential per unit charge of distance along the field line at that point-the field strength at any point Gravitational field strength the force per unit mass on a small mass placed in the field Gravitational force an attractive force that acts equally on any two objects due to their mass Kepler's third law for any planet, the cube of its mean radius of orbit is directly proportional to the square of its time period Universal constant of gravitation/ Gravitational constant the constant of proportionality in Newton's law of gravitation Electrical conductors an object that can conduct electricity Free electrons electrons in a conductor that move about freely inside the metal because they are not attached to a particullar atom Gold leaf electroscope a device used to detect electric charge Insulating materials a material that cannot conduct electricity Electric field strength the force per unit charge on a small positively charged object at a point in an electric field Electric potential the work done per unit charge on a small positively charge object in an electric field to ove it from infinity to that point in the field Equipotentials a line or surface in a field along which the electric or gravitational potential is constant Coulomb's law for two point charges Q1 and Q2 at distance apart r, the force between the two charges Capacitance the charge stored per unit pd of a capacitorunit- farad (F)= 1 coulomb per volt Time constant the time taken for a quantity that decreases exponentially to decrease to 0.37 (=1/e) of its initial value Capacitor energy energy stored by the capacitor Capacitor discharge through a fxed resistor of resistance R, time constant= FC Motor effect the force on a current-carrying conductor due to a magnetic field Fleming's left-hand rule rule that relates the directions of the force, magnetic field and current on a current-carrying conductor in a magnetic field Magnetic flux density the magnetic force per unit length per unit current on a current carrying conductor at right angles to the field lines Simple electric motor an electric motor with an armature consisting of a single coil of insulated wire Hall probes a device used to measure magnetic flux density Magnetic force Electromagnetic induction/ Induced emf the generation of an emf when magnetic flux linkage through a coil changes or a conductor cuts across magnetic field lines Fleming's right-hand rule/ Dynamo rule rule that relates the directions of the induced current, magnetic field and velocity of the conductor when the conductor cuts across magnetic field lines and an emf is induced in it Lenz's law when a current is induced by electromagnetic induction, the direction of the induced current is always such as to oppose the change that causes the current Magnetic flux equals BA for a uniform magnetic field of flux density B that is perpendicular to an area A Magnetic flux linkage through a coil of N turns, = NBA Faraday's law of electromagnetic induction the induced emf in a circuit is equal to the rate of change of magnetic flux linkage through the circuit Transformer converts the amplitude of an alternating pd to a different valueit consists of two insulated coils, the primary and secondary coil, wound round a soft iron laminated core Step-up transformer a transformer in which the rms pd across the secondary coil is less than the rms pd applied to the primary coil Step-down transformer a transformer in which the rms pd across the secondary coil is greater than the rms pd applied to the primary coil Transformer rule the ratio of the secondary voltage to the primary voltage is equal to the ratio of the number of secondary turns to the number of primary turns Transformer Efficiency for an ideal transformer the output power equals the input power Eddy currents unwanted induced currents in the metal parts of ac machines National Grid System the network of transformers and cables that is used to distribute electrical power from power stations to users Back emf emf induced in the spinning coil of an electric motor or in any coil which the current is changingacts against applied p.d. Authorkoolcookie11 ID122655 Card SetPhysics A2 Level DescriptionKey Words Unit 4 Updated2011-12-15T09:48:21Z Show Answers