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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 force
 Second law: the rate of change of momentum of an object is proportional to the resultant force on it
 Third 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 m_{1} and m_{2} at distance r apart is given by F=Gm_{1}m_{2}/r^{2}

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=v^{2}/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


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 drag
 1.Lightly damped system: amplitude of oscillations decreases gradually
 2.Heavily damped system: the system slowly returns to equilibrium without oscillating
 3.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 capacitor
 unit 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 currentcarrying conductor due to a magnetic field

Fleming's lefthand rule
rule that relates the directions of the force, magnetic field and current on a currentcarrying 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


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 righthand 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 value
 it consists of two insulated coils, the primary and secondary coil, wound round a soft iron laminated core

Stepup transformer
a transformer in which the rms pd across the secondary coil is less than the rms pd applied to the primary coil

Stepdown 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 changing
 acts against applied p.d.

