Physics

• Energy

  Never created or destroyed, only transferred between different forms and objects
• Forms of energy

  • Thermal or internal energy
  • Kinetic energy
  • Gravitational potential energy
  • Elastic potential energy
  • Chemical energy
  • Magnetic energy
  • Electrostatic energy
  • Nuclear energy
• Types of energy transfer

  1. Mechanical

  2. Electrical

  3. Heating

  4. Radiation (light or sound waves)
• System

  Collection of matter
• Open system

  Can exchange energy with the outside world
• Closed system

  Separate from the outside world, no exchange of matter or energy
• Work done

  Energy transferred
• Types of work done

  • Mechanical
  • Electrical
• Life cycle of stars

  1. Big cloud of dust and gas (nebula)

  2. Gravity pulls dust and gas together to form a protostar

  3. Protostar gets bigger and denser

  4. Temperature and pressure increase

  5. Hydrogen nuclei fuse to form helium (nuclear fusion)

  6. Star becomes a main sequence star

  7. Main sequence star has balanced outward and inward pressure

  8. Star runs out of hydrogen

  9. Gravity contracts star

  10. Nuclear fusion forms heavier elements up to iron
• Main sequence star


  Star in the stable stage of its life cycle, where nuclear fusion of hydrogen to helium is occurring
• Star runs out of hydrogen

  Gravity contracts the star
• Life cycle of a red giant star

  1. Star expels outer layers

  2. Leaves behind a hot dense solid core (white dwarf)

  3. White dwarf cools to become a black dwarf
• White dwarf


  Hot dense solid core of a star that remains after the outer layers are expelled
• Black dwarf


  White dwarf that has cooled to the point where it no longer emits light
• Life cycle of a red supergiant star

  1. Star undergoes more nuclear fusion

  2. Star eventually explodes in a supernova

  3. Supernova ejects heavy elements across the universe

  4. If star was very big, it condenses into a neutron star

  5. If star was extremely massive, it collapses into a black hole
• Supernova


  Massive explosion of a red supergiant star
• Neutron star


  Dense core left behind after a supernova of a large star
• Black hole


  Extremely dense object formed from the collapse of a massive star, with gravity so strong that even light cannot escape
• How transformers work in the national grid

  1. Electricity generated at power stations

  2. Passed through step-up transformers to increase voltage to 400,000V

  3. Transmitted across country in wires and pylons

  4. Passed through step-down transformers to decrease voltage to 230V for use in houses
• Transformer


  Device that increases or decreases the voltage of electricity
• How a single transformer works

  1. Alternating potential difference applied to primary coil

  2. Causes current flow and alternating magnetic field

  3. Alternating magnetic field in primary coil induces alternating magnetic field in iron core

  4. Alternating magnetic field in iron core induces potential difference in secondary coil
• More turns in secondary coil than primary coil

  Voltage is stepped up
• Fewer turns in secondary coil than primary coil

  Voltage is stepped down
• Newton's first law

  A resultant force is required to change the motion of an object
• If there isn't a resultant force, the object's motion won't change
• This principle works for both stationary and moving objects
• If the resultant force on a stationary object is zero, it will remain stationary
• Newton's second law

  If a non-zero resultant force acts on an object, it will cause the object to accelerate
• Particle with unbalanced forces

  • Resultant force to the right
  • Particle will accelerate to the right
• Newton's first law

  A resultant force is required to change the motion of an object
• Acceleration can result in 5 different things depending on the initial motion of the object
• Acceleration is defined as the change in velocity divided by the change in time
• Newton's first law


  • Applies to both stationary and moving objects
  • If resultant force is zero, object's motion won't change
• Circular motion like the orbit of the moon involves acceleration even with constant speed, because the direction is changing
• Newton's second law equation

  Force = Mass x Acceleration
• Newton's second law

  If a non-zero resultant force acts on an object, it will cause the object to accelerate
• Example calculation of acceleration using Newton's second law
• Inertia

  The tendency for the motion of an object to remain unchanged
• Resultant force on an object

  Causes acceleration in the direction of the force
• Inertial mass measures how difficult it is to change an object's velocity