A Level Physics Important Definitions
Advanced Subsidiary
Term/ Concept Definition
Experiment
Accuracy The closeness of the measured values to the t rue value
Precision The closeness of agreement between measured values
Force and Motion
Velocity Rate of change in displacement per unit time
Speed Rate of change in distance per unit time
Acceleration Rate of change in velocity per unit time
Scalar Only has magnitude
Vector Has both magnitude and direction
Newton When a 1 kg object has acceleration of 1ms-2
Thinking distance The distance travelled from seeing a reason to stop to the
moment that brakes are applied
Braking distance The distance travelled from the time brake is applied to the
vehicle stops
Stopping distance Sum of thinking distance and braking distance
Moment Product of force and the perpendicular distance of the pivot
Principle of moment For a body at rotational equilibrium, the sum of
anticlockwise moments about a point is equal to the sum of
clockwise moments about the same point
Couple Product of the forces and the perpendicular distance between
the forces
Centre of mass A point where any externally applied forces produce straight
line motion but not rotation
Centre of gravity An imaginary point where the entire weight appears to act
Density Mass per unit volume of a substance
Pressure Force per unit cross sectional area
Archimedes’ principle The upthrust of an object is equal to the weight of fluid it
displaces
Energy, Work, Power
Energy the capacity to do work
Gravitational Potential Energy Energy of an object due to its position in a gravitational field.
Kinetic Energy Energy due to motion of an object with mass
Power The rate of work done
Watt 1 watt is equivalent to 1Js-1
Work The product of force and the distance moved in the direction
of the force (in Joules)
A joule A unit of energy used when a force of 1N moves through 1m
in the direction of force
The conservation of energy The total energy of a closed system remains constant —
Energy cannot be created nor can be destroyed
Potential Stored
Efficiency The ratio of useful energy output to the total energy input,
often expressed in percentage
Materials
, Hooke’s law The force applied is proportional to the extension of the spring
unless the limit of proportionality is exceeded
Limit of proportionality The value of stress or force beyond which stress is no longer
directly proportional to strain
Elastic limit The elastic deformation becomes plastic deformation
Elastic deformation Removal of stress or force will return the object to its original
shape and size
Plastic deformation Removal of the stress and or force produces permanent
deformation
Tensile stress The force applied per unit cross sectional area of the wire
Tensile strain The fractions change in the original length of the wire
Young modulus The ratio of tensile stress to tensile strain when these
quantities are directly proportional to each other, measured
in Pa
Yield Point A point which there is rapid extension
Breaking strength The stress value at the point of fracture, calculated by dividing
the breaking force by the cross-sectional area
Ultimate tensile strength The maximum stress that a material can withstand before it
breaks
Brittle Shows no plastic deformation in high stress
Ductile Has a large plastic region in stress strain graph
Laws of motion and Momentum
Newton’s First Law An object will remain at rest or continue to move with
constant velocity if there is no resultant force applied
Newton’s Second Law The rate of change of momentum of an object is directly
proportional to the resultant force and takes place in the
direction of the force
Newton’s Third Law When two objects interact, they exert equal and opposite
forces on the other during the interaction
Momentum Mass multiplied by the velocity
The principal of conservation of For a closed system in interacting objects, the total momentum
momentum of the system is constant, unless an external force acts
Elastic collision A collision in which kinetic energy is conserved
Inelastic collision A collision in which kinetic energy is transferred to other
forms
Impulse The product of force and the time for which the force acts
Electrical Circuits
Coulomb 1 coulomb of electrical charge passes a point in one second
when there is an electric current of one ampere, (1C=1As)
Elementary Charge Equivalent to the charge on a proton, 1.6x10-19 C
Conservation of electric charge The electric charge cannot be created or destroyed, the total
charge of in any interaction must be the same before and after
the interaction
Kirchhoff’s first law At any point in an electrical circuit, the sum of currents into
that point is equal to the sum of currents out of that point,
electrical charge is conserved
Kirchhoff’s second law In a closed circuit, the sum of all electromotive force is equal
to the sum of all the potential differences
Mean drift velocity The average velocity of the electrons as they travel down the
wire, colliding with positive metal ions
Voltage Potential difference across a component when 1J of energy is
transferred per unit charge passing through the component
Advanced Subsidiary
Term/ Concept Definition
Experiment
Accuracy The closeness of the measured values to the t rue value
Precision The closeness of agreement between measured values
Force and Motion
Velocity Rate of change in displacement per unit time
Speed Rate of change in distance per unit time
Acceleration Rate of change in velocity per unit time
Scalar Only has magnitude
Vector Has both magnitude and direction
Newton When a 1 kg object has acceleration of 1ms-2
Thinking distance The distance travelled from seeing a reason to stop to the
moment that brakes are applied
Braking distance The distance travelled from the time brake is applied to the
vehicle stops
Stopping distance Sum of thinking distance and braking distance
Moment Product of force and the perpendicular distance of the pivot
Principle of moment For a body at rotational equilibrium, the sum of
anticlockwise moments about a point is equal to the sum of
clockwise moments about the same point
Couple Product of the forces and the perpendicular distance between
the forces
Centre of mass A point where any externally applied forces produce straight
line motion but not rotation
Centre of gravity An imaginary point where the entire weight appears to act
Density Mass per unit volume of a substance
Pressure Force per unit cross sectional area
Archimedes’ principle The upthrust of an object is equal to the weight of fluid it
displaces
Energy, Work, Power
Energy the capacity to do work
Gravitational Potential Energy Energy of an object due to its position in a gravitational field.
Kinetic Energy Energy due to motion of an object with mass
Power The rate of work done
Watt 1 watt is equivalent to 1Js-1
Work The product of force and the distance moved in the direction
of the force (in Joules)
A joule A unit of energy used when a force of 1N moves through 1m
in the direction of force
The conservation of energy The total energy of a closed system remains constant —
Energy cannot be created nor can be destroyed
Potential Stored
Efficiency The ratio of useful energy output to the total energy input,
often expressed in percentage
Materials
, Hooke’s law The force applied is proportional to the extension of the spring
unless the limit of proportionality is exceeded
Limit of proportionality The value of stress or force beyond which stress is no longer
directly proportional to strain
Elastic limit The elastic deformation becomes plastic deformation
Elastic deformation Removal of stress or force will return the object to its original
shape and size
Plastic deformation Removal of the stress and or force produces permanent
deformation
Tensile stress The force applied per unit cross sectional area of the wire
Tensile strain The fractions change in the original length of the wire
Young modulus The ratio of tensile stress to tensile strain when these
quantities are directly proportional to each other, measured
in Pa
Yield Point A point which there is rapid extension
Breaking strength The stress value at the point of fracture, calculated by dividing
the breaking force by the cross-sectional area
Ultimate tensile strength The maximum stress that a material can withstand before it
breaks
Brittle Shows no plastic deformation in high stress
Ductile Has a large plastic region in stress strain graph
Laws of motion and Momentum
Newton’s First Law An object will remain at rest or continue to move with
constant velocity if there is no resultant force applied
Newton’s Second Law The rate of change of momentum of an object is directly
proportional to the resultant force and takes place in the
direction of the force
Newton’s Third Law When two objects interact, they exert equal and opposite
forces on the other during the interaction
Momentum Mass multiplied by the velocity
The principal of conservation of For a closed system in interacting objects, the total momentum
momentum of the system is constant, unless an external force acts
Elastic collision A collision in which kinetic energy is conserved
Inelastic collision A collision in which kinetic energy is transferred to other
forms
Impulse The product of force and the time for which the force acts
Electrical Circuits
Coulomb 1 coulomb of electrical charge passes a point in one second
when there is an electric current of one ampere, (1C=1As)
Elementary Charge Equivalent to the charge on a proton, 1.6x10-19 C
Conservation of electric charge The electric charge cannot be created or destroyed, the total
charge of in any interaction must be the same before and after
the interaction
Kirchhoff’s first law At any point in an electrical circuit, the sum of currents into
that point is equal to the sum of currents out of that point,
electrical charge is conserved
Kirchhoff’s second law In a closed circuit, the sum of all electromotive force is equal
to the sum of all the potential differences
Mean drift velocity The average velocity of the electrons as they travel down the
wire, colliding with positive metal ions
Voltage Potential difference across a component when 1J of energy is
transferred per unit charge passing through the component
