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

Official definitions taken from numerous text books and compiled into a clear table to make revision more easier and less frustrating in always having to turn pages when definitions are forgotten!

- Created by: James Rushworth
- Created on: 09-12-10 20:18

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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

conserved

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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