forces, space and radioactivity

• newton's 1st law:

  an object will remain at rest or in uniform motion in a straight line unless acted upon by an external resultant force.
• newton's 2nd law:

  resultant force = mass x acceleration (f=ma)
• newton's 3rd law:

  if a body A exerts a force on body B then body B exerts an equal and opposite force on body A.
• energy efficiency of vehicles:

  • aerodynamic losses reduced by more streamlined designs.
  • rolling resistance is reduced by having correctly inflated tyres and using materials which don't heat up as much as they are squashed.
  • stop-start systems reduce idling losses.
  • inertial losses are reduced by having lighter cars.
• safety features:

  • in terms of work done: i.e. an air bag and a crumple zone increase the distance over which the energy is transferred, so reducing the force.
  • in terms of momentum: i.e. the same change in momentum happens over a longer time so there is decreased deceleration so the force decreases.
• features of the solar system:

  • order of the planets: mercury/venus/earth/mars/jupiter/saturn/uranus/neptune.
  • asteriod belt located between mars and jupiter.
  • mercury/venus/earth/mars are the rocky planets (the inner planets).
  • the remaining planets (the outer planets) are made from gas.
• au and light years:

  • 1 a.u. is the mean distance from the sun to earth.
  • 1 light year is the distance that light will travel in 1 year.
• life cycle of a star:

  stars of a similar mass to the sun:

  protostar -> main sequence star -> red giant -> white dwarf

  high star mass:

  protostar -> main sequence star -> supergiant -> supernova -> neutron star or balck hole
• stability of stars:

  • in the main sequence the forces acting on a star are balanced.
  • gravitational inward forces match the outwards combination of gas and radiation pressure forces.
  • when the hydrogen reduces the star will begin to fuse helium and then other increasingly heavier elements to maintain fusion.
  • the star will begin to swell as the combination of gas and radiation pressure exceeds the gravitational force and the forces become unbalanced.
  • eventually the gravitational force exceeds the combination of gas and radiation pressure and star shrinks.
• return of heavy material:

  heavy elements which are created in fusion in large stars are ejected during supernovae.
• origin of the solar system:

  • gravitational forces cause the matter to get closer together creating the sun and the planets.
  • during formation rocks tended to gather close to the sun and formed rocky planets whilst gaseous substances gathered together at the distances further away and formed the gas planets.
• isotope:

  isotopes of the same elements have equal numbers of protons but differing numbers of neutrons in their nuclei.
• unstable nuclei:

  radioactive emissions occur from unstable atomic nuclei due to an imbalance between the numbers of protons and neutrons in the nucleus.
• radioactive decay:

  a spontaneous process where unstable atomic nuclei transform, releasing radiation and becoming more stable.
• alpha radiation:

  helium nucleus

  
• beta radiation:

  high energy electron

  
• gamma radiation:

  electromagnetic wave