PHYSICS REVISION GUIDECh1: Physical MeasurementSI units: metre, kg, second, ampere, Kelvin, mole, candela.Derived: volume, density.1.2 MeasurementUncertainty = 0.5x the smallest value.Random error: lots of slightly different readings.Experimental error: problem with measuring device/method.Percentage uncertainty = uncertainty/valueAdding values = add uncertainties.Ch2: Mechanics2.1 KinematicsVelocity = displacement per unit time.Speed = distance travelled per unit time.Relative velocity = subtract the vectors.Acceleration = velocity/timeAverage velocity = displacement/timeSUVATS:a = (v - u)/ts = (u + v)t/2s = ut + 0.5at2v2 = u2 + 2asPositive displacement/velocity = body moving right.2.2 Free-Fall MotionOn Earth, bodies fall with an acceleration of 9.81ms-2.When falling, air resistance will push you up more and more until you cannot go faster.Area beneath a velocity-time graph = displacement.

2.4 Projectile Motion

SUVAT for horizontal motion: R = v cos tSUVAT for vertical motion: h = v2sin2/2g and t = 2vsin/g2.5 Forces and DynamicsGravitational force: W = mg. (W = weight).Free body diagrams show the forces acting on objects.2.6 Newtons First Law of MotionFirst law: A body will remain at rest or move with constant velocity unless acted upon by an external unbalanced force.Examples: mass on a string (T = mg), parachutists (force up = force down), car (force left = force right).Translational equilibrium: all forces are balanced.2.7 Force and AccelerationMomentum, = mv.Impulse: movement due to the effect of something.Impulse is the change in momentum.Newtons second law of motion: the rate of change of momentum of a body is directly proportional to the unbalanced force acting on that body, and takes place in the same direction.So, F = ma.2.8 Newtons Third LawNewtons third law of motion: if body A exerts a force on body B then body B will exert an equal and opposite force.Example: a box on the floor, water hitting a wall.Law of conservation of momentum: in a system of isolated bodies, the total momentum is always the same.Area under a force-time graph = impulse.2.9 Work, Energy, PowerWork done = force x distance moved in direction of force.In general: Work = Fcos x s ( is the angle between s and F).Work done by a varying force: use average force, or find the area under a force-distance graph.F/s = K (spring constant).Gravitational potential energy (PE): the energy a body has due to its position above the Earth. PE = mgh.Law of conservation of energy: energy can be neither created or destroyed - only changed from one form to the other.Elastic collision: when both momentum and KE are conversed.Inelastic collision - momentum/KE not conserved. For example when two bodies stick together (energy is taken to squash them together so KE is lost).Sharing of energy: when a body explodes, the smaller part gets the most energy.Power: work done per unit time (J/s or W).Efficiency: (power in/power out) x 100 (for a percentage).2.10 Uniform Circular MotionTime period (T) - time for one cycle. Angular displacement () - the angle swept by a line.Angular velocity () - 2/TFrequency (f) - 1/T.All bodies moving in a circle accelerate towards the centre.Centripetal force, F = mv2/r = m2r (e.g. ball on a string, car on a bend, wall of death).Ch3: Thermal Physics3.1The mole: 6.022 x 1023 atoms/molecules of an element.Internal energy: the material of the object takes energy, molecules vibrate more. The total internal energy of a substance is the total PE and random KE of the molecules.Heat flows from hot to cold between two touching bodies until a thermal equilibrium is reached.C to K: add 273.3.2 Thermal Properties of MatterThermal capacity (c): the amount of heat needed to raise the temperature of a substance by 1C. Unit: JC-1. Given by: C = Q/TSpecific heat capacity (C): the amount of heat required to raise the temperature of 1kg of a substance by 1C. Unit: JC-1.When matters change state, the energy used enables the molecules to move more freely (KE is the same), so temperature does not change.Boiling takes place throughout the liquid, at the same temperature.Evaporation takes place at the surface only, at all temperatures. Faster molecules escape, average KE decreases, temperature decreases.Specific latent heat (L): the amount of heat needed to change the state of 1kg of the material without a change in temperature. Unit: JKg-1. L = Q/m.Solid to liquid: latent heat of fusion.Liquid to gas: latent heat of vaporisation.3.3 Kinetic Model of an Ideal Gas- Molecules are perfectly elastic-Molecules are perfect, tiny spheres-Molecules are identical-There are no forces between the molecules, except when they collide, so they move with constant velocity-The molecules are very small; their total value is much smaller than the volume of the gasThe temperature is a measure of the average KE of the molecules of an ideal gas.Increase in temperature and decrease in volume always increases pressure. Pressure = force/area.Doing work on a gas = increase in KE = increase in temperature and pressure.3.4 ThermodynamicsAbsolute zero: the temperature of the gas when the pressure is zero. The point at which the molecules stop moving. -273C, 0K.A fixed point used to define the temperature scale is something observable. The one used to define the absolute temperature scale is the triple point water - the temperature at which it exists as a solid, liquid and gas at equilibrium (0.01C).Equation of state for an ideal gas: PV = nRT. (R = 8.31).Isobaric: constant pressure.Isochoric: constant volume.Isothermal: constant temperature.Adiabatic: no heat exchanged (Q = 0).A real gas: forces between molecules as the pressure/volume decreases. This makes them change to a liquid, unless the temperature is very high.3.5 Thermodynamic ProcessesA thermodynamic system is a collection of bodies that can do work on each other and transfer heat. In IB we only use the gas piston example.Work done = P x V.Gas does work = pushes piston out = positive.Work done on gas = piston drops down = negative.Area under a pressure-volume graph = the work done.First law of thermodynamics: if a gas expands and gets hot, heat must have been added. This is a statement of the principle of energy conservation.Q = U + W. (U is internal energy, Q is amount of heat added).Isobaric: temperature, internal energy and work done decrease. Q is negative.Isochoric: volume stays the same, temperature and internal energy increase. Q is positive.Adiabatic contraction: volume is reduced, work done is negative, temperature/internal energy increase.

A-B: isochoric temperature rise (gas gets hot, heat added).B-C: isobaric expansion (heat added = increase in internal energy and volume).C-D: isochoric temperature drop (gas gets cold and loses work to surroundings).D-A: isobaric compression (heat lost = work done on the gas, volume decrease).

Net work done = difference between work done on gas and work done by gas. Equal to enclosed area on the diagram.A-B: isothermal (work done by gas = heat gained).B-C: adiabatic (gas does work and cools down).C-D: isothermal (work done so it cools down).D-A: adiabatic (work done on gas, gas gets hotter).

3.6 Second Law of ThermodynamicsSecond law: it is not possible to convert heat completely into work.This implies that thermal energy cannot spontaneously transfer from a region of low temperature to a region of high temperature. Heat flows from hot to cold. Particles fly in random directions. Molecules start ordered, but start to collide and become disordered.Rewritten: in any thermodynamic process, the total entropy always increases (e.g. a fridge: food gets colder, more ordered. Room is given heat, less ordered).Entropy of a system = the amount of disorder in the system/the spreading out of energy.Change in entropy, S = Q/T(JK-1)Ch4: Simple Harmonic Motion and WavesCycle: 1 complete oscillation (2 for a circle).Equilibrium position: the place it would rest if undisturbed/displacement = 0.Amplitude (x0): maximum displacement.Time period (T): time taken for 1 cycle.Frequency (f): number of complete cycles in one second.Angular frequency (): = 2f. (2rads s-1 is one revolution per second).SHM: acceleration is proportional to the distance from a fixed point. Acceleration is always directed towards a fixed point. a = -2x.Displacement-time graph: x = x0 cos tVelocity-time graph: v = -v0 sin tAcceleration-time graph: a = -a0 cos tSpeed = circumference/time period = 2r/T, but 2r/T = , so speed = .Centripetal acceleration= v2/r = 2r2/r = 2rAcceleration = -2xMaximum velocity = x0V =

4.2 Energy Changes During SHMKE is max when displacement is zero (it is stationary at x0). KEmax = 0.5m2x02 or 0.5m2(x02 - x). PE = 0.PE is max when the bob is at the highest displacement. PE = 0.5mv02cos2t = 0.5m2x2.If KE and PE graphs are added together, it gives a constant value known as the total energy. ET = m2x02.4.3 Forced Oscillations and ResonanceIn oscillating systems there is always friction and sometimes air resistance. The system has to do work against these, resulting in a loss of energy. This is called damping (for example, dampers in a cars suspension to absorb the shock of a bump).Light damping: small opposing forces, gradual energy loss, amplitude decreases over time.Critical damping: resistive force is so large it returns to its equilibrium position.Natural frequency: the frequency the oscillation is naturally at.Forced oscillation: when the system is forced to oscillate at a different frequency.Resonance: an increase in amplitude that causes the system to oscillate at its natural frequency.Out of phase: two identical waves moving at different times.Phase difference: the amount they are out of phase by. If completely, it is .4.4 Wave CharacteristicsWave pulse: when a disturbance can be seen travelling from one end to the other.Continuous progressive waves move with SHM in the shape of a sine curve.Transverse waves: disturbance is perpendicular to the direction of the waves.Longitudinal waves: disturbance is parallel.v = f (velocity = distance/time, therefore v = /1/f = f).All electromagnetic waves travel with the same speed in free space.4.5 Wave PropertiesWavefront: line joining points that are in a phase.Rays: shows the direction of the waves. Always at a right angle to waves.Circular wavefront: caused by a point disturbance.Plane wavefront: extended disturbance.Reflection: wave hits barrier and bounces back. The normal is drawn at 90 degrees. The angle of incidence = angle of reflection. The incident and reflected rays are in the same plane as the normal. In a change of medium, some waves pass through (transmitted) and others are reflected.Refraction: there is a change in velocity when there is a change in medium. Wave hits boundary at an angle and there is a direction change.Snells Law: sin i / sin r = v1/v2 (angles of incidence and refraction)The ratio is called the refractive index. Larger = larger angle.Diffraction: takes place when a wave passes through a small opening/aperture. If the path difference = d, then the phase angle, = d/Coherent waves = identical waves.A polarized wave travels in one direction.4.6 Standing (Stationary) WavesPeaks move up and down but do not progress = a standing wave. Occurs when identical waves travelling in opposite directions superpose.Node: place on the wave that doesnt move at all.Anti-node: max amplitude.