OCR (A) Unit G484 [Physics A2] key definitions

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OCR (A) Unit G484 [Physics A2] key definitions
Term Definition
Newtonian laws of motion
Newton's 1st law An object will remain at rest or keep travelling at a constant velocity
unless an external force acts on it
Newton's 2nd law The net force of an object is equal to the rate of change of its
momentum (net force and change are in the same direction)
Newton's 3rd law When two bodies interact, the forces they exert on each other are
opposite and equal
Momentum The product of an objects mass and its velocity
Impulse The product of the force and the time for which it acts
Perfectly Elastic Collision Kinetic energy is conserved- momentum and total energy are always
Inelastic collision Kinetic energy is not conserved- it is transferred into other forms such
as heat. Momentum and total energy are always conserved
Circular motion
Centripetal acceleration The acceleration toward the centre of the circle that holds the object
in elliptical orbit.
Centripetal force The net force acting on an object moving in a circle- is always directed
towards the centre of the circle
Gravitational field strength The gravitational force experienced by an object per unit mass
Newton's law of Any two point masses attract each other with a force which is directly
gravitation proportional to the product of their masses and inversely proportional
to the square of their separation
Period (related to a circle) The time taken for an object to complete one orbit
Kepler's 3rd law The square of the period ,T, of a planet is directly proportional to the
cube of its distance, r, from the sun (T2 is proportional to r3)
Geostationary orbit The orbit of an artificial satellite which has a period equal to one day
so that it stays in the same point above the earth's equator (from
Earth the satellite appears to be stationary)
Simple harmonic motion
Displacement Distance travelled by a particle from its equilibrium
Amplitude The maximum displacement of a particle from its equilibrium position
Period The time taken for one complete oscillation of a vibrating particle
Frequency The number of oscillations of a particle per unit time
Angular frequency The rate of change of angle (rads-1) [= 2/T]
Phase difference The fraction of an oscillation between the vibrations of two oscillating
particles (expressed in degrees or radians)
Simple harmonic motion When the acceleration of an object in an oscillating system is directly
proportional to the displacement from its equilibrium position, and is
directed towards the equilibrium position
Damping An oscillatory motion where the amplitude decreases over time due
to energy loss
Resonance The forced motion of an oscillator characterised by maximum
amplitude when the forcing frequency matches the oscillator's natural
frequency. A system absorbs maximum energy from a source when
the source frequency is equal to the natural frequency of the system
Solids, liquids, gases and
thermal physics
JR 2010

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Solid (Spacing, ordering, Spacing: Closely packed
motion) Ordering: Regular order
Motion: Vibrations about a fixed point
Liquid (S,o,m) Spacing: Closely packed (less packed than solids)- more gaps between
particles than solids
Ordering: Less regular order
Motion: Particles can move past each other slowly compared to gases
Gas (S,o,m) Spacing: Molecules far apart, not packed in at all
Ordering: Randomly ordered
Motion: Fast moving in random directions
Brownian motion The random movement of microscopic particles suspended in a liquid
or gas, caused by collisions with molecules…read more


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