Paper 2

• Everyday Speeds

  walking - 1.5m/s

  running - 3m/s

  cycling - 6m/s

  car - 25 m/s

  train - 55 m/s

  plane - 250 m/s
• Speed of sound

  300 m/s
• Work done

  Energy transferred when a force moves an object through a distance

  1J = 1Nm
• Elastically deformed


  Affected by more than one force and returns to original shape
• Inelastically deformed


  Affected by more than one force and does not return to original shape
• Moment = force x perpendicular distance from line of action to the pivot

  • imagine drawing a straight line through the point and in the direction that a force hits an object
  • draw a new line from this line to the pivot at 90°
  • this is the distance needed for the equation
• Pressure

  Force is applied at normal to all surfaces

  Pressure in a fluid is caused by collisions of particles and container
• Up thrust is equal to the mass of liquid displaced by an object
• On a velocity time graph, distance traveled is the area under the curve
• Newton's first law


  A resultant force of 0 is a constant speed
• Newton's second law


  • The larger the resultant force, the faster the object accelerates
  • Acceleration is inversely proportional to mass
  • F=ma
• Inertia


  How easy it is to change the velocity of an object

  inertial mass = resultant force/acceleration
• Newton's third law


  When two objects interact, the forces they exert are equal and opposite#
• Stopping distances


  • Thinking distance - affected by speed and reaction time
  • Braking distance - affected by speed, quality of brakes, quality of tyres and grip)
  • Speed is proportional to thinking distance
  • Speed² is proportional to braking distance
• Transverse waves oscillate perpendicular to the direction of energy transfer
• Features of waves

  • Frequency - numbers of complete waves passing a point in a second
  • Period - amount of time it takes for a complete wave to pass a point
  • period = 1/frequency
• Waves can be:

  absorbed - transferring energy to energy stores

  reflected

  transmissed - reflection
• • When a wave enters a new medium speed may change, this means wavelength may also be changed
  • Slower wave bends toward the normal
• Specular reflection - like a mirror

  vs

  diffuse reflection
• • Energy can cause an electron to change levels
  • When it falls back to the original level, an electromagnetic wave is produced
• • AC causes oscillating electric and magnetic fields therefore, EM waves
  • The radio waves are absorbed by a receiver and become kinetic energy causing electrons to oscillate causing AC
• Long waves can diffract around the Earth's curvature

  Short waves can bounce off the ionosphere
• Microwaves are used for satellite communication as they are not affected by the atmosphere

  Infra-red radiation is used in a toaster or an electric heater
• • High frequency electromagnetic radiation is much more dangerous than low frequency
  • Sievert - radiation dose, therefore risk of harm. Takes into account: amount of radiation absorbed; how harmful the type is and the type of tissue absorbing the rays
• • Temperature is the difference between IR radiation absorbed and IR radiation emitted
  • Black is a better emitter/receiver than white. Same with matt over shiny
• Required Practical - infra red radiation

  • Leslie cube empty on a heatproof mat
  • fill with boiling water
  • use a thermometer to measure the temperature of each face - should be equal
  • place an IR detector 10cm away from a face and record amount of IR radiation
  • Repeat for each face
• Required Practical - IR radiation and colour

  • stick two ball bearings to two metal plates with solid candle wax
  • Face the opposite side of each plate towards a flame
  • One plate has a black face, the other is silver
  • The ball on the black face will fall first
• • During the day, more radiation is absorbed than emitted
  • Local temperatures vary but the overall temperature of the Earth's surface is mostly constant
• • A sound wave speeds up in a denser material
  • Frequency stays the same
  • due to speed = frequency x wavelength, wavelength increases with speed
• Range of human hearing

  20Hz to 20KHz
• Ultra sound

  partial reflection - some waves are returned upon hitting a change of medium
• Seismic waves

  • P-wave - longitudinal -> faster in solid than liquid
  • S-wave - transverse -> cannot travel through fluids
  • P faster than S
  • Seismic waves tend to have gradually curved paths, but a kink is produced at a barrier
  • Therefore Earth's structure can be predicted
• Magnetic Fields

  Field lines go from North to South
• Magnetic field around a current carrying wire

  Right hand grip/screw rule

  • thumb in direction of current
  • Curve fingers
  • direction finger is the direction of magnetic field
• Solenoid


  • coil of wire
  • uniform field within the coil
• Motor effect


  Left hand rule

  • thumb - force
  • first finger - magnetic field direction
  • second finger - current direction
• Using the motor effect

  • the direction of the motor can be changed by either swapping positive and negative or north and south
  • A speaker uses this. Alternating current reflecting the frequency of the sound
• Generator effect

  alternators

  • slip rings
  • brushes
  • alternating current direction swaps each half turn

  dynamo

  • split-ring commutator
  • generates direct current
• More coils in a transformer equals more potential difference
• Life cycle of a star

  Nebula

  v

  Protostar

  v

  Main sequence star -> Red giant -> white dwarf -> black dwarf

  v

  Red super giant

  v

  Supernova -> black hole

  v

  Neutron star