OCR G484 Definitions
Module 1 – Newton’s Laws & Momentum
Newton’s 1st Law – An object will remain at rest or continue travelling at a
constant velocity, unless acted upon by an external force.
Newton’s 2nd Law – The change in momentum of an object is directly
proportional to the net force acting upon it; and takes place in the direction of
the net force.
Newton’s 3rd Law – When object A exerts a force on object B, object B exerts
a force that is equal, opposite in direction and of the same type on object A.
Impulse – The product of the force and the time for which it acts (FΔt). It
equals the change in momentum of a body (as well as the area under a forcetime graph.)
Perfectly Elastic Collisions – Collisions where both kinetic energy and
momentum are conserved.
Inelastic Collisions – Collisions where momentum is conserved, but kinetic
energy is not; it is transferred into other forms of energy (such as heat.)
The Newton – One Newton is the force that gives a mass of 1 kg an
acceleration of 1ms-2.
The Principle of Conservation of Momentum – In a closed system, the total
moment before a collision = the total momentum after a collision.
Module 2 – Circular Motion & Oscillations
The Radian – One radian is the angle subtended at the centre of the circle by
an arc length equal to the circle’s radius.
The Period – The time taken for a complete oscillation.
Centripetal Force – The net force acting on an object describing a circular path
– it is always directed towards the centre of the circle.
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Centripetal Acceleration – The acceleration towards the centre of the circle
that holds the object in elliptical orbit (a=v2/r).
Gravitational Field Strength – Force per unit mass.
Newton’s Law of Gravitation – The gravitational force of attraction between
two bodies is directly proportional to the product of their masses and inversely
proportional to the square of the distance between them.
Kepler’s 3rd Law – The square of the period of a planet is directly proportional
to the cube of its radius.
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.)
Displacement – The distance an object has travelled from its mean (or rest)
position.
Amplitude – The maximum displacement of a particle from its mean / rest /
equilibrium position.
Frequency – The number of oscillations per unit time at any point.
Angular Frequency – The change of angle per unit time (give in rads-1.)
Phase Difference – The fraction of an oscillation between the vibrations of two
oscillating particles (unit = degrees or radians.)
Simple Harmonic Motion – An object undergoing SHM:
• has an acceleration proportional to its displacement from a fixed point.
• accelerates in the opposite direction to the displacement.
Damping – An oscillatory motion where the amplitude is deliberately reduced
(energy loss.)
Resonance – the build-up of a large amplitude oscillation when two vibrating
objects have the same frequency.
Module 3 – Thermal Physics
Pressure – Force per unit cross-sectional area.
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Internal Energy – The sum of the random distributions of kinetic and potential
energies of all the molecules in a body.
Specific Heat Capacity – The energy required per unit mass of a substance to
raise its temperature by 1K (or 1 unit.)
Latent Heat of Fusion – The quantity of energy per unit mass required to
change a substance from a solid into a liquid, at constant temperature.
Latent Heat of Vaporisation – The quantity of energy per unit mass required
to change a substance from a liquid into a vapour, at a constant temperature.
Boyle’s Law – The volume of a fixed mass of gas is inversely proportional to
the pressure exerted on it, provided the temperature is kept constant.
Charles’ Law – The volume occupied by a gas at constant temperature is
directly proportional to its absolute temperature.
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