Definitions Flashcards
Vector
A physical quantity with magnitude and direction
Scalar
A physical quantity with magnitude only
Moment
Force times perpendicular distance from the line of action of the force to the point
Principle of moments
For an object in equilibrium, the sum of the clockwise moments is equal to the sum of the anticlockwise moments about any point
Couple
A pair of equal and opposite forces acting on a body, but not along the same line
Velocity
Change of displacement per unit time
Acceleration
Change of velocity per unit time
Newton’s 1st Law
An object will remain at rest or at a constant velocity unless acted on by an external resultant force
Newton’s 2nd Law
The force is proportional to the rate of change of momentum
Newton’s 3rd Law
For every action there is an equal and opposite reaction
Equilibrium
State of an object when at rest or moving at constant velocity
Density
Mass per unit volume of the substance
Stress
Force per unit area of cross section in a solid perpendicular to the cross section
Strain
Extension per unit length of a solid when deformed
Young’s Modulus
Tensile stress/strain
Limit of Proportionality
The limit beyond which, when a wire or a spring is stretched, its extension is no longer proportional to the force that stretches it
Plastic deformation
Deformation of a solid beyond its elastic limit
Elastic limit
Point beyond which a wire is permanently stretched
Hooke’s Law
The extension of a spring is directily proportional to the force applied to it, up to the limit of proportionality
Isotope
Atoms with the same number of protons but different numbers of neutrons
Conservation of energy
Energy cannot be created or destroyed, only converted from one form to another
Work done
Force times distance moved in the direction of the force
Ductile
Material that can be drwan into threads, it can be shaped or permanently deformed without fracture
Brittle
Material cannot be permanently stretched
Wave
Transfer energy from A to B via a medium of transfer, without transferring the medium
Standing wave
When two waves travel in opposing directions and they have the same wave speed, frequency and in general amplitude, they will superpose and form a standing wave
Monochromatic
Single wavelength
Coherent
No change in phase relationship
Collimated
Formed in a narrow beam
Diffraction
Spreading out or bending of waves as they pass through a gap or around an obstacle
Emf
Describes the amount of energy that is converted from one form to electrical and placed on a unit of charge at the source
Ohm’s Law
The current flowing through a metallic conductor is directly proportional to the potential difference across its ends, provided the temperature remains constant
Resistivity
The resistance of a piece of wire 1m in length and with a cross sectional area of 1m^2
Centre of mass
The point through which a single force on the body has no turning effect
Principle of conservation of linear momentum
The total linear momentum of a system of interacting bodies is constant, providing no external forces act
Work function
Minimum energy to liberate electron
Excitation
When an electrion takes in energy from a photon or collision and goes up an energy level
Ionisation
When an electron takes in enough energy to leave the atom
Motive power
Power outputted by a powered object (i.e. engine or muscle)
Progressive waves
Waves that move outwards from their source