paper 2

• scalar

  only magnitude
• vector

  magnitude and direction
• contact forces

  objects that are physically touching

  • friction, air resistance and tension
• non-contact forces

  the objects are physically separated

  • gravitational force, electrostatic and magnetic forces
• what is weight

  the force acting on an object due to gravity, depends on the gravitational field strength at the point where the object is
• what is the resultant force?

  a number of forces acting on an object being replaced by a single force that has the same effect as all the original forces acting together
• work done

  when a force causes an object to move through a distance causing displacement
• limit of proportionality

  the extension of a elastic object (spring), is directly proportionate to the force applied, provided that the limit of proportionality is not exceeded
• distance

  how far an object moves, not involving direction making it a scalar quantity
• displacement

  includes both the distance an object moves and the direction making it a vector quantity
• speed

  does not include direction making it a scalar quantity
• speed of typical values

  walking = 1.5 m/s

  running = 3 m/s

  cycling = 6 m/s

  speed of sound in air = 330 m/s
• velocity

  its speed given a direction making it a vector quantity
• newtons first law

  velocity will only change if a resultant force is acting upon the object

  the tendency of objects to continue in their state of rest or uniform motion is called 'inertia'

  if a resultant force acting on an object is zero

  • the object is stationary and remains stationary
  • if it's moving, it continues to move at the same speed and in the same direction and velocity
• newtons second law

  the acceleration of an object is proportional to the resultant force acting on the object, inversely proportional to the mass of the object

  • 'inertial mass' is a measure of how difficult it is to change the velocity of an object
• newtons third law

  whenever two objects interact, the forces they exert on each other are opposite and equal
• stopping distance

  the sum of the distance the vehicle travels during the driver's reaction time (thinking distance) and the distance it travels under the braking force (braking distance)

  the greater the speed of the vehicle the greater the stopping distance
• reaction time

  varies between 0.2 and 0.9 seconds

  • can be affected by tiredness, drugs and alcohol
• factors affecting braking distance

  can be affected by adverse road and weather conditions or poor conditions of the vehicle

  • such as icy or wet conditions and poor condition of brakes or tyres
• factors affecting braking distance

  when a force is applied to the brakes of a vehicle, the brakes and the wheels reduce the kinetic energy of the vehicle and the temperature of the brakes increases

  • the greater the speed the greater the braking force needed to stop the vehicle
  • the greater the braking force the greater the deceleration of the vehicle, this may lead to brakes overheating and loss of control
• conservation of momentum

  in a closed system, the total momentum before an event is equal to the total momentum after the event
• longitudinal waves

  show areas of compression and rarefaction, sound waves travelling through air are longitudinal

  • they have parallel oscillations in the direction of energy transfer
• transverse waves

  oscillations are perpendicular (90 degrees) to the direction of the energy transfer

  • all electromagnetic waves are transverse
  • ripples in waves in water
  • a wave on a string
• the amplitude of a wave

  the maximum displacement of a point on a wave from its undisturbed position
• wavelength

  the distance from a point on one wave to the equivalent point on the adjacent wave
• frequency

  the number of waves passing a point each second
• wave speed

  speed at which the energy is transferred through the medium
• electromagnetic waves

  transverse waves that transfer energy from the source of the waves to an absorber

  • they form a continuous spectrum and all types of electromagnetic waves travel at the same velocity through a vacuum of space or air
• spectrum of waves

  long wavelength and low frequency

  • Radio waves = red = real
  • Microwaves = orange = monkeys
  • Infrared = yellow = insist
  • Visible light = green = very
  • Ultraviolet = blue = useful
  • X-rays = indigo = xmas
  • Gamma rays = violet = gifts

  short wavelength and high frequency
• refraction

  when a wave crosses a boundary between two materials it changes the speed

  • if it's travelling along the normal, it will change speed but it's NOT refracted
  • if the wave hits the boundary at an angle then it is refracted
  • if it bends towards the normal it slows down
  • if it bends away from the normal it speeds up|
  • the higher the density of the two materials the slower the wave travels
• optical density

  the measure of how quickly light can travel through it, the higher the optical density the slower the wave travels through it
• ray diagrams

  show the path of a wave, show the direction a wave is travelling in

  • the normal = an imaginary line that's at a right angle of where the incoming ray hits the boundary
  • the angle between the incident ray and the normal is the angle of incidence
  • the angle of refraction is the angle between the refracted ray and the normal
  • if the second material is denser then the first the ray will bend TOWARDS the normal, if the angel of refraction is smaller then the angle of incidence the 2 material is denser
• wavefront diagrams

  a wavefront is a line showing all the points in a wave that are in the same position as each other after a given number of wavelengths

  • when a wave crosses a boundary at an angle, only part of 5he wave crosses the boundary at first
  • if it's travelling into a denser material, the part travels slower than the rest of the wavefront
• radio waves

  are made by oscillating charges and magnetic fields, alternating currents are made of oscillating charges

  • the frequency of the waves produced will be equal to the frequency of the AC
  • can produce radio waves using AC in an electrical current, the object in which charges oscillate is called a 'transmitter'
  • the energy carried by the waves is transferred to the electrons in the material of the receiver
  • this causes the electrons to oscillate and if the receive is part of a complete electrical circuit it generates a AC which has the same freq as the radio waves that generated it
• radio waves used for communication

  they are EM radiation with long wavelengths of 10 cm's

  • because long wavelengths (1-10km) diffract (bend) around the curved surface of the earth, this makes it possible for radio signals to be received even if the receiver isn't in the line of sight of the transmitter
  • short wavelengths (10-100m) these are reflected from the ionosphere (an electrically charged layer of the earths upper atmosphere)
• uses of electromagnetic waves

  radio waves – television and radio

  microwaves – satellite communications, cooking food

  infrared – electrical heaters, cooking food, infrared cameras

  visible light – fibre optic communications

  ultraviolet – energy efficient lamps, sun tanning

  X-rays and gamma rays – medical imaging and treatments.
• EM radiation

  high frequencies like UV can cause loads of damage, as they can cause the skin to permanently age and even cause blindness and risk of skin cancer

  the
• permanent and induced magnetism

  permanent magnets produce their own magnetic fields

  an induced magnet is a material that becomes a magnet when it is placed in a magnetic field and therefore always causes a force of attraction, when its removed it loses most of its magnetism quickly
• magnetic fields

  the region around a magnet where a force acts on another magnet or magnetic material (iron, nickel, steel or cobalt)

  • always from north to south
  • a magnetic compass contains a small bar magnet, the compass needle points in the direction of the earth's magnetic field
• electromagnetism

  When a current flows through a conducting wire a magnetic field is

  produced around the wire., the strength of the field depends on the current and the distance from the wire

  • shaping a wire to form a solenoid increases the strength of the magnetic field by creating a current through the wire, the magnetic field inside the solenoid is strong and uniform
  • adding an iron core to the solenoid increases the strength of the magnetic field
  • an electromagnet is a solenoid with an iron core