Physics paper 2

• Energy is not something you can hold in your hand, it's just an idea. It's a number that tells us what will happen when objects interact in what we call a system
• Total energy in any interaction is always conserved. Energy cannot be created or destroyed
• Energy can be turned into matter (Mass) but it's still technically true that energy is conserved
• Energy stores


  • Kinetic energy
  • Gravitational potential energy
  • Elastic potential energy
  • Thermal energy
  • Chemical potential energy
• Kinetic energy


  E = 1/2 mv^2, where m is mass and v is velocity
• Gravitational potential energy


  E = mgh, where m is mass, g is gravitational field strength, and h is height
• Elastic potential energy


  E = 1/2 kx^2, where k is the spring constant and x is the extension
• Thermal energy


  E = mcΔT, where m is mass, c is specific heat capacity, and ΔT is change in temperature
• Chemical potential energy is found in food and fuels, but there is no equation for it
• In a closed system, no energy is lost to the surroundings and no energy comes in from the surroundings
• Gravitational potential energy at the top of a roller coaster

  Kinetic energy at the bottom of the roller coaster
• Rearranging the kinetic energy equation to find velocity


  Double the kinetic energy, divide by mass, then square root
• If more gravitational potential energy is lost than kinetic energy gained, the difference is energy lost to the surroundings, so it is not a closed system
• Work


  Energy transferred by a force
• Specific heat capacity practical

  Use an electric heater, voltmeter, ammeter, balance, timer, and thermometer to measure the energy input and temperature change, then calculate specific heat capacity
• Power


  Rate of energy transfer, P = E/t
• Efficiency


  Ratio of useful energy output to total energy input, expressed as a decimal or percentage
• Force


  A push or pull, can be contact or non-contact
• Forces


  • Can be represented as vectors
  • Balanced forces result in no acceleration
  • Unbalanced forces result in acceleration
• Scalar


  A quantity with magnitude but no direction
• Vector


  A quantity with both magnitude and direction
• Weight


  The force due to gravity acting on an object, calculated as mass x gravitational field strength
• Hooke's Law


  Force = spring constant x extension, for elastic deformation
• Moment


  A turning force, calculated as force x perpendicular distance to pivot
• Pressure


  Force per unit area, p = F/A
• Gas pressure


  Due to collisions of gas particles with surfaces, affected by number of particles, volume, and temperature
• Electricity is the flow of charge (electrons) that carries energy from a source to a component where the energy is released
• Factors that increase the rate of collisions between gas particles

  • Reducing the volume
  • Raising the temperature
  • Increasing the temperature (also increases kinetic energy and momentum of collisions)
• Higher altitude


  Atmosphere becomes less dense due to fewer particles in a given volume, hence pressure decreases
• Electricity


  The flow of charge or charges like electrons, carrying energy from a source to a component where the energy is released as another type of energy
• Simple electric circuit


  1. Cell/battery has a store of chemical potential energy

  2. Energy transferred to electrons moving through wires

  3. Electrons pass through bulb, energy converted to light and heat

  4. Electrons pushed back to battery to be refilled with energy
• Potential difference (PD) or voltage

  Measure of how much energy is transferred per 'kum' (group) of electrons
• Current


  Rate of flow of electric charge
• Resistance


  Property of components that resists the flow of current, causing energy transfer (e.g. heat in resistor, light in bulb)
• Increasing PD


  Results in greater current flowing, PD and current are directly proportional
• Ohm's law


  PD (V) = Current (I) x Resistance (R)
• Resistance of metal


  • Increases with higher PD and current due to more collisions between electrons and metal ions
• Diode


  Component that only allows current to flow in one direction
• LED (light-emitting diode)


  Diode that emits light when current flows through it
• Measuring resistance of a wire

  1. Measure V and I, then use Ohm's law to calculate R

  2. Vary length of wire to see how resistance changes