Junior Cert Physics Definitions
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Volume - space an object occupies
Mass - amount of matter in a
substance
Density = mass / volume
Energy - ability to do work
Force - anything that causes a change
in velocity
Pressure = force / area
• Lever
- rigid body free to turn about a fixed
point called a fulcrum
• Moment - turning effect of a force, = force
x distance
• Momentum
- mass x velocity
• Law of Lever - when a lever is balanced the
sum of the moments on the L.H.S. = sum of the
moments on the R.H.S.
• Centre of Gravity - point at which all the bodies
weight appears to act
• Weight = mass x gravity
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Hooke’s Law – extension of an elastic material is
directly proportional to the applied force producing the
extension
Newton’s law – If no force acts on a body then a body
in motion will continue at a constant speed in a straight
line
Displacement - shortest distance between two
points, straight line
Speed = distance / time
Velocity - speed in a given direction i.e 50m/s
north
acceleration = change in velocity / time
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Law of conservation of energy - energy
cannot be created or destroyed but can
be changed from one form to another
Friction - is a force between any two
materials in contact with each other
which opposes their motion
Work = force x distance
Pressure in a liquid depends on depth
and density
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Temperature is a measure of the hotness of a body
Heat – is a form of energy that moves from hotter to
colder bodies
Heat travels by
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Conduction through a solid, no movement of the substance
Convection through liquids and gases, movement of particles
Radiation ( can travel through vacuum ), by means of waves
Latent heat - is the heat needed to change the state
of a substance without changing the temperature i.e
ice melting, boiling water
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Increased pressure - increases boiling
point
A body will float in a liquid if it is less
dense
Power is the amount of work done per
second
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Potential difference - difference in charge so that
current will flow
Current – is the flow of charge (electrons) Amp. No.
electrons per second
Ohm’s Law - at a constant temperature Voltage =
Current x resistance ( V = I x R )
ESB unit - kilowatt hour
kilowatts x hours
Fuse – a thin piece of wire with a low melting point that
breaks the circuit if the current is too high
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Resistor – controls the amount of current in a
circuit Ohms
The EMF of a battery – the pull of the electrons
in a circuit- electromotive force
A body becomes positively charged if it looses
electrons and negatively charged if it gains
electrons.
Insulator – is a substance that holds charge
A conductor – is a material that allows charge
to flow through it.
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Direct current (D.C) – the flow of charge
in one direction only (battery)
Alternating current (A.C) – current that
changes direction (mains)
A diode – device that allows current to
flow in one direction only
Light emitting diode (LED) – gives out
light when current flows through it
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Light dependent resistor (LDR) – a
variable resistor whose resistance
changes with the amount of light that
falls on it.
Switch – device to complete / break a
circuit
Insulator – does not allow heat /
electricity to flow through them
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Echo – Reflected sound from a solid
object
Ultra sound – sound of very high pitch,
not heard by humans
Refraction - bending of light as it
passes from one transparent medium to
another
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Luminous body – creates its own light,
Sun
Non-luminous body – Reflects light
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Energy forms
Kinetic - any moving object
Potential - due to position / condition stretched
elastic / spring
Sound - vibrating objects
drum
Radiant - light and heat
sun
Chemical - between the bonds of elements
Nuclear - in the nucleus of an atom
Internal - potential and kinetic energy of molecules
Electric - object that needs to be plugged in
radio
/ tv
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Dispersion - breaking up of white light
into seven colours ( spectrum )
Opisometer - measures short curved
lines
Power = I x V = I2 x R