Unit 2 Definitions
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Unit 2 Definitions
Definitions
A VectorA vector is any physical quantity that has direction as well as magnitude
A Scalar A scalar is any physical quantity that has magnitude but is not directional
The moment of a Force  The moment of a force about a point is defined as the force x the perpendicular distance from the line of action of the force to the point
The Principle of moments  The sum of the clockwise moments equals the sum of the anticlockwise moments for a system in equilibrium.
Centre of mass  The centre of mass of a body is the point through which a single force on the body has no turning effect.
A Couple  is a pair of equal and opposite forces acting on a body, but not along the same line.
Torque  The moment of a couple is the torque. It is given by force x perpendicular distance between the lines of action of the force.
Mass  is a measure of an ojects inertia (resistance to change of motion)
Weight  is the force due to gravity acting on an object. It is given by W=mg, where g is the acceleration due to gravity
Displacement  is distance in a given direction
Speed  is defined as change of distance per unit time
Velocity  is defined as change of displacement per unit time
Acceleration  is defined as change of velocity per unit time.
Projectile motion  A projectile is any object acted upon only by the force of gravity. The object moves on a parabolic path.
Projectile like motion  Any form of motion where the object experiences a constant accleration in a different direction to its velocity will be like projectile motion. The object moves on a parabolic path.
Newton's first law of motion  Objects stay at rest or in uniform motion unless acted upon by a resultant force.
Newton's second law  The resultant force is proportional to the acceleration F=ma
Newton's third law  Action and reaction are equal and opposite.
Definitions  Waves
Transverse Waves  Waves in which the direction of the vibrations is perpendicular to the direction in which the wave travels.
Longitudinal Waves  Waves in which the direction of the vibrations is parallel to the direction in which the wave travels.
Plane polarised waves  are waves in which the vibrations stay in one plane. Only transverse waves can be plane polarised.
Unpolarised waves  are waves in which the vibrations change from one plane to another.
Displacement  of a vibrating particle is its distance and direction from its equilibrium position.
Amplitude  of a wave is the maximum displacement of a vibrating particle.
Wavelength  of a wave is the least distance between two particles vibrating in phase (same displacement and velocity at same time)
Time Period  is the time for 1 complete wave to pass a point.
Frequency  is the number of cycles (complete waves) passing a point per second.
Phase difference  between two vibrating particles is the fraction of a cycle between the vibrations of the two particles, measured in degrees or radians.
Progressive wave  Progressive waves travel through a substance (or space if electromagnetic) and transfer energy.
Stationary wave  A stationary wave is a wave pattern with nodes and antinodes, which are formed when 2 progressive waves of the same frequency and amplitude pass through each other. They do not transfer energy through space.
The principle of superposition  states that when two waves meet, the total displacement at a point is equal to the sum of the individual displacements at that point.
Node  is a fixed point in a stationary wave where the amplitude is zero.
Antinode  is the fixed point in a stationary wave where the amplitude is a maximum.
Interference  formation of pints of cancellation and reinforcement where two coherent waves pass through each other.
Coherent Waves  are waves with the same frequency and constant phase difference.
Refraction  change of direction of a wave when it crosses a boundary where its speed changes.
Refractive index  speed of light in free space/ speed of light in a substance.
Total internal reflection  A light ray travelling in a substance is totally internally reflected at a boundary with a substance of lower refractive index, if the angle of incidence is greater than the critical angle.
Critical Angle  the angle of incidence must exceed the critical angle for total internal reflection to occur.
Optical Fibre  a thin flexible transparent fibre used to carry light pulses from one end to the other
Multipath dispersion  the lengthening of a light pulse as it travels along an optical fibre, due to rays that repeatedly undergo total internal reflection having to travel a longer distance than the rays that undergo less total internal reflection.
Spectral dispersionthis can occur if white light is used in an optical fibre. The speed of light in the glass depends on the wavelength. Violet light travels more slowly than red light. The violet light falls behind the faster red light causing the white light pulse in the optical fibre to become longer.
Monchromatic Light  this is light of a single wavelength. (a laser is a good example of this  it is highly monchromatic)
Coherent bundle of fibres (as with medical endoscope) The fibres at each end are in the same relative positions.
Diffraction  is the spreading out of waves as they pass through a gap or close to an edge
Diffraction Grating  is a plate with many closely spaced parallel slits.
Maximum Order (diffraction grating)  the maximum order is given by d/wavelength rounded DOWN to the nearest whole number.
Materials Definitions
Density – of a substance is the mass per unit volume
Hooke’s Law – states that the force needed to stretch a spring is directly proportional to the extension of the spring, within the limit of proportionality
Limit of Proportionality – the limit beyond which the extension of a wire or spring is no longer proportional to the force that stretches it.
Spring Constant or stiffness constant – the force per unit extension needed to extend a wire or spring
Tensile Stress –tensile force per unit area
Tensile Strain – ratio of extension to original length
Young’s Modulus – the ratio of tensile stress to tensile strain.
Elastic Limit – the point beyond which a wire is permanently extended (this is plastic deformation)
Ultimate Tensile Stress – this is where a wire loses strength, it is the maximum stress it can withstand before it breaks (sometimes called the breaking stress)
Brittle – A brittle material breaks without noticeable yield – it breaks without deforming
Ductile – A ductile material undergoes plastic deformation before breaking, it can be easily drawn into wires
A VectorA vector is any physical quantity that has direction as well as magnitude
A Scalar A scalar is any physical quantity that has magnitude but is not directional
The moment of a Force  The moment of a force about a point is defined as the force x the perpendicular distance from the line of action of the force to the point
The Principle of moments  The sum of the clockwise moments equals the sum of the anticlockwise moments for a system in equilibrium.
Centre of mass  The centre of mass of a body is the point through which a single force on the body has no turning effect.
A Couple  is a pair of equal and opposite forces acting on a body, but not along the same line.
Torque  The moment of a couple is the torque. It is given by force x perpendicular distance between the lines of action of the force.
Mass  is a measure of an ojects inertia (resistance to change of motion)
Weight  is the force due to gravity acting on an object. It is given by W=mg, where g is the acceleration due to gravity
Displacement  is distance in a given direction
Speed  is defined as change of distance per unit time
Velocity  is defined as change of displacement per unit time
Acceleration  is defined as change of velocity per unit time.
Projectile motion  A projectile is any object acted upon only by the force of gravity. The object moves on a parabolic path.
Projectile like motion  Any form of motion where the object experiences a constant accleration in a different direction to its velocity will be like projectile motion. The object moves on a parabolic path.
Newton's first law of motion  Objects stay at rest or in uniform motion unless acted upon by a resultant force.
Newton's second law  The resultant force is proportional to the acceleration F=ma
Newton's third law  Action and reaction are equal and opposite.
Definitions  Waves
Transverse Waves  Waves in which the direction of the vibrations is perpendicular to the direction in which the wave travels.
Longitudinal Waves  Waves in which the direction of the vibrations is parallel to the direction in which the wave travels.
Plane polarised waves  are waves in which the vibrations stay in one plane. Only transverse waves can be plane polarised.
Unpolarised waves  are waves in which the vibrations change from one plane to another.
Displacement  of a vibrating particle is its distance and direction from its equilibrium position.
Amplitude  of a wave is the maximum displacement of a vibrating particle.
Wavelength  of a wave is the least distance between two particles vibrating in phase (same displacement and velocity at same time)
Time Period  is the time for 1 complete wave to pass a point.
Frequency  is the number of cycles (complete waves) passing a point per second.
Phase difference  between two vibrating particles is the fraction of a cycle between the vibrations of the two particles, measured in degrees or radians.
Progressive wave  Progressive waves travel through a substance (or space if electromagnetic) and transfer energy.
Stationary wave  A stationary wave is a wave pattern with nodes and antinodes, which are formed when 2 progressive waves of the same frequency and amplitude pass through each other. They do not transfer energy through space.
The principle of superposition  states that when two waves meet, the total displacement at a point is equal to the sum of the individual displacements at that point.
Node  is a fixed point in a stationary wave where the amplitude is zero.
Antinode  is the fixed point in a stationary wave where the amplitude is a maximum.
Interference  formation of pints of cancellation and reinforcement where two coherent waves pass through each other.
Coherent Waves  are waves with the same frequency and constant phase difference.
Refraction  change of direction of a wave when it crosses a boundary where its speed changes.
Refractive index  speed of light in free space/ speed of light in a substance.
Total internal reflection  A light ray travelling in a substance is totally internally reflected at a boundary with a substance of lower refractive index, if the angle of incidence is greater than the critical angle.
Critical Angle  the angle of incidence must exceed the critical angle for total internal reflection to occur.
Optical Fibre  a thin flexible transparent fibre used to carry light pulses from one end to the other
Multipath dispersion  the lengthening of a light pulse as it travels along an optical fibre, due to rays that repeatedly undergo total internal reflection having to travel a longer distance than the rays that undergo less total internal reflection.
Spectral dispersionthis can occur if white light is used in an optical fibre. The speed of light in the glass depends on the wavelength. Violet light travels more slowly than red light. The violet light falls behind the faster red light causing the white light pulse in the optical fibre to become longer.
Monchromatic Light  this is light of a single wavelength. (a laser is a good example of this  it is highly monchromatic)
Coherent bundle of fibres (as with medical endoscope) The fibres at each end are in the same relative positions.
Diffraction  is the spreading out of waves as they pass through a gap or close to an edge
Diffraction Grating  is a plate with many closely spaced parallel slits.
Maximum Order (diffraction grating)  the maximum order is given by d/wavelength rounded DOWN to the nearest whole number.
Materials Definitions
Density – of a substance is the mass per unit volume
Hooke’s Law – states that the force needed to stretch a spring is directly proportional to the extension of the spring, within the limit of proportionality
Limit of Proportionality – the limit beyond which the extension of a wire or spring is no longer proportional to the force that stretches it.
Spring Constant or stiffness constant – the force per unit extension needed to extend a wire or spring
Tensile Stress –tensile force per unit area
Tensile Strain – ratio of extension to original length
Young’s Modulus – the ratio of tensile stress to tensile strain.
Elastic Limit – the point beyond which a wire is permanently extended (this is plastic deformation)
Ultimate Tensile Stress – this is where a wire loses strength, it is the maximum stress it can withstand before it breaks (sometimes called the breaking stress)
Brittle – A brittle material breaks without noticeable yield – it breaks without deforming
Ductile – A ductile material undergoes plastic deformation before breaking, it can be easily drawn into wires
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