# AS unit 2 revision notes for physics

whole of unit 2

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• Created on: 23-05-11 21:52

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Mechanics Materials
Moment of a force about a point is defined as force x Hookes lawthe force (needed to stretch a
perpendicular distance from the point to the line of spring is directly) proportional to the
action of the force extension (of the spring from its natural
length) up to the limit of proportionally
Torque. Couple of a pair of equal and opposite forces defined as
Elastic limitthe maximum amount that a
force x perpendicular distance between the lines of action of the
forces. material can be stretched (by a force) and still
Centre of mass of a body is the point through which a single
removed
force on the body has no turning effect Stress==T/A which is force per unit area of
Displacement distance in a given direction from a certain point crosssection in a solid perpendicular to the
Object moving at a constant speed on a circle radius r ..... cross section
Strain=L/L which is extension per unit
Terminal speed..................... length of a solid when deformed
Describe and explain how the acceleration of the ball changed Breaking stresstensile stress needed to break a
after it entered the liquid until it reached the bottom of the solid material
cylinder? Plastic behaviour
The ball decelerates/slows down in the fluid, because a force due to Elastic strain energy
fluid friction/resistance/viscosity acts (upwards) Fractureseparation into two under stress
on the ball, (and) the force due to the fluid is greater than the weight of
Brittlenessliable to break suddenly without
the ball, resistive force is upwards resistive force decreases, The
deceleration decreases (to zero), because the force due to fluid deforming plastically
friction/resistance/viscosity decreases, Stress strain graphgradient is young modulus,
as the balls speed decreases until it is equal (and opposite) to the Force (Y) ­extension (X) area underneath
weight of the ball,(or the resultant force is zero) gradient of graph energy stored in stretched spring.
gives the acceleration and the ball moves at constant/terminal Plastic deformation material is permantly
velocity/a=0 stretched
· Newtons 3 laws, each force has an opposite and equal reaction
force, F=ma, resultant force is needed to change velocity Elastic deformationmaterial returns to original
· Thrust=mg+ma, tension in tow bar=ma, engine force=Ma+ma, car shape when forces removed
acceleration=force/mass
· Thinking distance=speed X reaction time, Breaking
distance=v2/2a, Impact time=2s/u+v
· Power rate of transfer of energy
Horizontal component=X=Ut
Vertical = y=1/2gt2
Waves Measure mass of unknown substance
Longitudinalparticle vibration or oscillation is the same as the use a metre rule to measure the length of the spring, when
direction of propagation or energy transfer e.g. sound it supports a known mass and when it supports the
Transverse particle vibration or oscillation is perpendicular to unknown mass, repeat for different (standard) mass,
direction of propagation or energy transfer e.g. EM waves accuracy use a set square or other suitable method to
Polarisation is evidence for the nature of transverse waves, use in
measure the position of the lower end of the spring
sunglassesreduce glare, 3d glassesenhanced viewing experience,
stress analysisreveals areas of high and low stress against the (vertical) mm rule, plot graph of mass against
Light is transmitted through polarising filter when their transmission length (or extension), read off mass corresponding to
axes are parallel to each other when their transmission axes are at 90 to length (or extension) due to the sample, the extension of
each other , the second filter no longer transmits light, the spring = length unscratched length, mass of rock
Polarising filter always appears slightly grey because it absorbs all sample = extension of spring supporting known
incident light except the component that's aligned with its own
transmission axes, as rotated through 360 intensity will vary between
mass/extension of spring supporting rock sample(known
maxima and minima mass)
Optical fibresrefraction towards normal, they are made narrow to Measure Young modulus
reduce multipath or multimode dispersion, which would cause light describe/show means of applying a load/force to a wire
travelling at different angles to arrive at different times , or to prevent ,measure original length, measure extension, measure
light/data/signal loss (from core or fibre)(which would cause) signal
diameter, extension = extension length original length,
to get weaker, or crossover will make data less secure use of rule/ruler/tape measure, measure diameter with
Optical fibres communicationshigh speed internet, medical
endoscopesimprove medical diagnosis micrometer, use of travelling microscope to measure
The formation of stationary waves by two waves of the same frequency extension, or extension of, wire measured with vernier
travelling in opposite directions scale, varying load/mass, repeat readings (of length or
Total internal reflection takes place at the corecladding boundary so extension), diameter measured in several places, change in
the light rays stay in the core. If two fibres are in contact, light cannot
pass from one fibre to the other because it is confined to the core of
diameter monitored (with micrometer),explain how
each fibre. Without cladding, the cores would be in contact and light crosssectional area is found using A = r2
could pass from one fibre to another where they are in contact Light
signals in each fibre would therefore not be secure, stops core from
scratching, keeps signal safe, provides strength given core is thin

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Path differencethe difference in distances from two Equilibrium
coherent sources to an interference fringe
Coherencewave source has constant phase difference resultant force must be zero ! (or forces
Monochromatic lightsingle wavelength balance)
Laser source of coherent monochromatic light
two source and single source doubleslit systems for the resultant torque must be zero ! (or acm = cm