Definitions for CIE AS Level Physics
All the definitions you require are on here and are arranged by chapter. They were taken
from mark schemes and so are exactly what you need to know. Remember that if you
understand the topic, the definition will be easy to memorise! :D
Anything underlined means that that word is essential. If it is in (brackets) that means that it
isn’t as important. Definitions in red means that I have never seen it asked before on a
paper, but it is good to know and understand them.
Scalar - a scalar has magnitude (only)
Vector - a vector has magnitude and direction
Accuracy - accuracy is determined by the closeness of the measurement to the true value
Precision - precision is determined by the range of the values/measurements
Uncertainty - the total range of values within which the measurement is expected to lie
Physical quantity - quantity with a magnitude and a unit
Speed - distance moved/time taken
Velocity - the rate of change of displacement
Displacement - Displacement is the distance in a specified direction from a point
Acceleration - change in velocity/time taken OR the rate of change of veloctiy
Newton’s First Law: a body continues at (rest or) constant velocity unless acted upon by a
resultant force
Newton's Second Law - For a body of constant mass, its acceleration is directly
proportional to the resultant force applied to it. OR The resultant force on a body is
proportional to the rate of change of its momentum.
Newton’s Third Law - When 1 body exerts a force on another, the second body exerts an
equal and opposite reaction force on the first.
Force - the rate of change of momentum
1 newton - the amount of force that will give a 1kg mass an acceleration of 1ms-2 in the
direction of the force.
, Momentum - product of its mass and velocity
Principle of conservation of momentum - The total momentum remains constant provided
there is no external resultant force acting on a system of interacting bodies OR the sum of
total momentum before = sum of total momentum after in an isolated system of interacting
bodies.
Impulse - If a constant force acts on a body for Δt the impulse of the force is given by FΔt.
AND the impulse of a force is equal to the change in momentum
Elastic collision - KE before a collision = KE after a collision
Inelastic collision - The total KE before and after are not equal. Even if KE is not
conserved, momentum and total energy is always conserved.
Viscous force - the frictional force in a fluid
Mass - mass is the property (of a body/object) resisting changes in motion OR mass is the
quantity of matter (in a body)
Weight - the force due to the gravitational field/force/gravity which acts on an object
Moment of a force - the product of the force and the perpendicular distance of the line of
action of the force from the pivot Fxd units are Nm AND the turning effect of a force
Couple - 2 forces which are equal in magnitude but opposite in direction whose lines of
action do not coincide
Torque - product of 1 of the forces and the perpendicular distance between the forces
Principle of moments - for a body to be in rotational equilibrium, the sum of the clockwise
moments about any point must equal to the sum of the anticlockwise moments about any
point.
Centre of gravity - CG of an object is the point at which the whole weight of the object may
be considered to act
Centre of mass - the point through which a single force on the body has no turning effect
Equilibrium - sum of the forces in any direction must be 0 and sum of the moments of the
forces about any point must be 0.
Density - mass per unit volume
Pressure - the force per unit area where F acts perpendicularly to A. Also p=ρgh in fluids
All the definitions you require are on here and are arranged by chapter. They were taken
from mark schemes and so are exactly what you need to know. Remember that if you
understand the topic, the definition will be easy to memorise! :D
Anything underlined means that that word is essential. If it is in (brackets) that means that it
isn’t as important. Definitions in red means that I have never seen it asked before on a
paper, but it is good to know and understand them.
Scalar - a scalar has magnitude (only)
Vector - a vector has magnitude and direction
Accuracy - accuracy is determined by the closeness of the measurement to the true value
Precision - precision is determined by the range of the values/measurements
Uncertainty - the total range of values within which the measurement is expected to lie
Physical quantity - quantity with a magnitude and a unit
Speed - distance moved/time taken
Velocity - the rate of change of displacement
Displacement - Displacement is the distance in a specified direction from a point
Acceleration - change in velocity/time taken OR the rate of change of veloctiy
Newton’s First Law: a body continues at (rest or) constant velocity unless acted upon by a
resultant force
Newton's Second Law - For a body of constant mass, its acceleration is directly
proportional to the resultant force applied to it. OR The resultant force on a body is
proportional to the rate of change of its momentum.
Newton’s Third Law - When 1 body exerts a force on another, the second body exerts an
equal and opposite reaction force on the first.
Force - the rate of change of momentum
1 newton - the amount of force that will give a 1kg mass an acceleration of 1ms-2 in the
direction of the force.
, Momentum - product of its mass and velocity
Principle of conservation of momentum - The total momentum remains constant provided
there is no external resultant force acting on a system of interacting bodies OR the sum of
total momentum before = sum of total momentum after in an isolated system of interacting
bodies.
Impulse - If a constant force acts on a body for Δt the impulse of the force is given by FΔt.
AND the impulse of a force is equal to the change in momentum
Elastic collision - KE before a collision = KE after a collision
Inelastic collision - The total KE before and after are not equal. Even if KE is not
conserved, momentum and total energy is always conserved.
Viscous force - the frictional force in a fluid
Mass - mass is the property (of a body/object) resisting changes in motion OR mass is the
quantity of matter (in a body)
Weight - the force due to the gravitational field/force/gravity which acts on an object
Moment of a force - the product of the force and the perpendicular distance of the line of
action of the force from the pivot Fxd units are Nm AND the turning effect of a force
Couple - 2 forces which are equal in magnitude but opposite in direction whose lines of
action do not coincide
Torque - product of 1 of the forces and the perpendicular distance between the forces
Principle of moments - for a body to be in rotational equilibrium, the sum of the clockwise
moments about any point must equal to the sum of the anticlockwise moments about any
point.
Centre of gravity - CG of an object is the point at which the whole weight of the object may
be considered to act
Centre of mass - the point through which a single force on the body has no turning effect
Equilibrium - sum of the forces in any direction must be 0 and sum of the moments of the
forces about any point must be 0.
Density - mass per unit volume
Pressure - the force per unit area where F acts perpendicularly to A. Also p=ρgh in fluids
