P2

P2

1. 1 - Motion

   • 1.1 Distance-time Graphs
     • Describe the motion of an object
     • Speed is the distance travelled each second
     • Gradient represents speed
     • Horizontal = stationary
     • Straight line = constant speed
     • Speed(m/s) = distance travelled(m) / time taken(s)
   • 1.2 Velocity and Accelatation
     • Velocity is speed in a given direction
     • Acceleration(m/s2) = (final velocity(m/s) - initial velocity(m/s)) / time(s)
       • Negative answer = deceleration
   • 1.3 More About Velocity-time Graphs
     • Gradient = acceleration
       • Negative gradient = decelaration
     • Horizontal = no acceleration
     • Area under the line = distance travelled in given time
   • 1.4 Using Graphs
     • Gradients
       • Velocity graph = acceleration
       • Distance graph = speed
     • Area under velocity graph = distance travelled

2. 2 - Forces

   • 2.1 Forces Between Objects
     • Objects always exert equal and opposite forces
     • Weight always acts down
   • 2.2 Resultant Force
     • The single force that would have the same effect on the object as all the original forces acting together
     • Resultant force is 0
       • If at rest will stay at rest
       • If moving will stay at same velocity
     • Resultant force not 0
       • Acceleration in direction of force
       • If object moving in opposite direction to force it will decelerate
   • 2.3 Force and Acceleration
     • Resultant force(N) = mass(kg) x acceleration(m/s2)
     • Bigger the force, bigger the acceleration
   • 2.4 On the Road
     • If at steady speed, resultant force 0
       • Equal and opposite forces
     • Stopping distance = thinking distance + braking distance
       • Thinking distance increased if tired / use of drugs
       • Braking distance increased if roads / car in bad condition
   • 2.5 Falling Objects
     • Resultant force(N) = mass(kg) x acceleration(m/s2)
     • Weight(N) = mass(kg) x accel. due to gravity(m/s2)
       • If not falling, g = gravitational field strength(N/kg)
     • Earth = 10m/s2
     • Falling through fluids
       • Fluid exerts drag force on object
       • Drag force increases until equal to weight, making terminal velocity so no acceleration
   • 2.6 Stretching and Squashing
     • An elastic object regains original shape when forces deforming it are removed
     • Extension is directly proportional to the force applied
       • When limit of proportionality is reached this doesn't apply
     • Force(N) = spring constant(N/m) x extension(m)
       • The stiffer the spring, the greater the constant
   • 2.7 Force and Speed
     • Reducing speed reduces fuel used (fuel economy)

3. 3 - Work, Energy and Momentum

   • 3.1 Energy and Work
     • When energy is transferred, work is done
     • Work done(J) = force(N) x distance(m)
       • If distance moved = 0 then no work is done
     • Work done to overcome friction is transferred by heating
   • 3.2 Gravitational Potential Energy
     • Energy stored because of the object's position in the earth's gravitational field
     • Change in gravitational potential energy(J) = mass(kg) x gravitational field strength(N/kg) x change in height(m)
     • Power(W) = energy(J) / time(secs)
   • 3.3 Kinetic Energy
     • Greater mass and higher speeds both increase kinetic energy
     • Kinetic energy(J) = 0.5 x mass(kg) x speed(m/s)
   • 3.4 Momentum
     • All moving objects have momentum
     • Momentum(kgm/s) = mass(kg) x velocity(m/s)
     • Conservation of momentum: total momentum before = total momentum after
   • 3.5 Explosions
     • One part moves one way, the other moves the opposite with the same force, thus conserving the momentum
     • E.g. a gun
     • One represented as plus, the other as minus
       • Minus means opposite direction
   • 3.6 Impact Forces
     • If impact time is short, force is larger
     • Impact time: the time taken for a collision to take place
     • Crumple zones
       • Increase impact time, reducing force
   • 3.7 Car Safety
     • Crumple zones
     • Seat belts
       • Spreads force
     • Air bags
       • Spreads force

4. 4 - Current electricity

   • 4.1 Electrical Charges
     • When two insulating materials rub together, electrons transfer from one material onto the other
       • One that loses electrons becomes positive
       • One that gains electrons becomes negative
       • Charging by friction
     • Opposite electric charges attract, same electric charges repel
       • The further the materials the weaker the force
   • 4.2 Electric Circuits
     • Current(A) = charge(C) / time(secs)
   • 4.3 Resistance
     • Current is measured with an ammeter placed in series with the component
     • Potential difference is measured with a voltmeter and is placed in parallel with the component
     • Potential difference(V) = work done(J) / charge(C)
       • Work done can also be energy
     • Resistance(ohms) = pd(V) / current(A)
     • Ohms law
       • Current is directly proportional to pd
       • Anything that obeys this is an ohmic conductor
   • 4.4 More Current-Potential Difference Graphs
     • Filament bulb
       • Curved line
       • Resistance increases as current increases as resistance increases as temperature increases
       • Reversing pd makes no difference to curve
     • Diode
       • Current flows in one direction only
       • In reverse directoin diode has high resistance so current = 0
     • LDR
       • As light increases resistance decreases
     • Thermistor
       • As temperature increases resistance decreases
   • 4.5 Series Circuits
     • If there's a break anywhere current stops flowing
     • Current through each component is the same
     • V=IxR
     • Pd is shared between components, so sum of all components = supplied pd
     • Sum of components' resistance = total resistance of circuit
   • 4.6 Parallel Circuits
     • If there's a break in one branch, current can still flow through all other parts
     • Pd across each component is equal
     • Total current = sum of each component

5. 5 - Mains Electricity

   • 5.1 Alternating Current
     • Current that reverses direction, found in mains electricity
     • Frequency = the number of times it changes / second
       • UK mains = 50hz
     • UK mains 230V
     • Live wire
       • Alternates between + and - potential
       • Peak voltages of +325 and -325
         • = 230v pd
     • Neutral wire
       • Stays at 0
     • Frequency of AC(Hz) = 1 / time for one cycle(secs)
   • 5.2 Cables and Plugs
     • Pins made of brass as conductors and wont rust / oxidise
     • Brown wire = live pin
     • Blue wire = neutral pin
     • Yellow and green wire = earth pin
       • A two core cable has no earth wire
       • Appliances with metal casing must be connected to earth wire
         • If fault appears, the object could become live
       • Appliances with a plastic casing don't need to be earthed
     • The more current that needs to be carried, the thicker the casing needs to be
   • 5.3 Fuses
     • Cut off appliance from live wire if fuse blows
     • When fault develops in earthed appliance, current flows to earth and blow fuse
     • Rating should be just higher than appliance's current
       • Too low = blows straight away
       • Too high = doesn't blow quickly enough
     • Circuit breakers
       • electromagnetic switch that opens if current > x value
       • RCCB
         • Cuts current in live wire if different to neutral wire
         • Works faster
   • 5.4 Electrical Power and Potential Difference
     • Power is rate of energy transfer
     • Power(W) = energy(J) time(secs)
     • Power(W) = current(A) x potential difference(V)
       • Fuses should be slightly higher than power
     • Pd of mains = 230V
   • 5.5 Electrical Energy and Charge
     • Current = rate of flow of charge
     • Charge(C) = current(A) x time(secs)
     • Energy transferred(J) = potential difference(V) x charge(C)
   • 5.6 Electrical Issues
     • Faults occur as a result of damage
     • Filament and halogen bulbs are less efficient than low energy bulbs as don't last as long
     • Don't touch if current >30V

6. 6 - Radioactivity

   • 6.1 Observing Nuclear Radiation
     • Nuclei of radioactive substances are unstable and become stable through radioactive decay
     • Radioactive decay
       • Substances emit radiation and turn into different elements
       • Unpredictable, random process
       • Not affected by external conditions
     • Types of radiation
       • Alpha
         • Relative charge +2
       • Gamma
         • No charge or mass
       • Beta
         • Relative charge -1
     • Background radiation
       • Environment
       • X-Ray machines
       • Space
   • 6.2 The Discovery of the Nucleus
     • Plum pudding model
       • Spheres of positive charge with electrons stuck in
       • Early idea about atoms
     • Alpha particle scattering
       • Most of the atom is empty space
         • Most particles went through foil
       • Large positive charge
         • Some particles deflected through small angles
         • Repelled by another positive charge
       • Large mass
         • A few rebounded through large angles
   • 6.3 Nuclear Reactions
     • Alpha decay
       • Loses 2 protons and 2 neutrons
         • Emitted as alpha particles
       • Once emitted, atomic number -2 and mass number -4
     • Beta decay
       • Neutron changes to proton and electron
         • Electron emitted
       • Once emitted, atomic number+1 and mass number no change
     • Charged particle = ion
     • Different number of neutrons = isotope
     • Gamma radiation
       • Electromagnetic wave
   • 6.4 More About Alpha, Beta and Gamma Radiation
     • When travelling through a material, atoms collide with atoms of material, knocking electrons off, creating ions
       • Ionisation
         • Can kill / damage a living cell if happens inside it
     • Alpha
       • Relatively large
       • Strongly ionising
       • Lots of collisions
       • Don't penetrate far into a material
         • Can be stopped by air, skin, paper
       • Deflected by electric and magnetic fields
         • Positive charge
     • Beta
       • Smaller and faster than alpha
       • Less ionising
       • Penetrate further
         • Stopped by aluminium or a few meters of air
       • Deflected by electric and magnetic fields in opposite direction
         • Negative charge
     • Gamma
       • Travel a long way before colliding
         • electromagnetic
       • Weakly ionising and deeply penetrating
         • Stopped by lead or concrete
       • Not delfected
         • No charge
   • 6.5 Half Life
     • Radioactivity decreases over time
       • Different isotopes decrease at different rates
     • Time for count rate to decrease to half its origonal rate
       • Same for any sample of the same isotope
   • 6.6 Radioactivity at Work
     • Alpha
       • Smoke alarms
         • Needs half life of several years
       • Poorly penetrating so not dangerous
     • Beta
       • Thickness monitoring
       • Long half-life for accurate measurements
       • Tracers in medicine
     • Gamma
       • Tracers in medicine
         • Half life of a few hours to cause no damage

7. 7 - Energy From the Nucleus

   • 7.1 Nuclear Fission
     • The splitting of an atomic nucleus
     • Common include uranium and plutonium
     • Nucleus absorbs a neutron, nucleus splits, energy released
     • Chain reaction occurs when fission causes further fission
   • 7.2 Nuclear Fusion
     • When two nuclei are forced together to form a single larger nucleus
     • Caused by two light nuclei colliding at a very light speed
     • Must be heated to high temperatures so they don't repel eachother
     • Contained by a magnetic field
   • 7.3 Nuclear Issues
     • Causes of background radiation
       • Radon gas from radioactive substances
       • Cosmic background radiation from space
       • Food and drink
       • Air travel
   • 7.4 The Early Universe
   • 7.5 The Life History of a Star
   • 7.6 How the Chemical Elements Formed

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