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


  Different types of energy
• Kinetic energy


  Calculated using E = 1/2 mv^2 (mass x velocity^2)
• Gravitational potential energy (GPE)

  Calculated using E = mgh (mass x gravitational field strength x height)
• Elastic potential energy


  Calculated using E = 1/2 kx^2 (spring constant x extension^2)
• Thermal energy


  Calculated using E = mc∆T (mass x specific heat capacity x temperature change)
• 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. Energy must be transferred from one object to another or one store to another
• Gravitational potential energy (GPE) at the top of a roller coaster


  Converted to kinetic energy (KE) at the bottom
• The equation for kinetic energy can be rearranged to find the speed of an object
• The equation for gravitational potential energy can be rearranged to find the speed of an object using the height it falls from
• If the total energy at the top of a roller coaster is greater than the kinetic energy at the bottom, the difference must have been lost to the surroundings, meaning it is not a closed system
• Work is another word for energy transferred by a force
• Specific heat capacity practical

  Use an electric heater, voltmeter, ammeter, balance, timer, and thermometer to measure the specific heat capacity of a material
• Power


  The rate of energy transferred, calculated using P = E/t (power = energy/time)
• Efficiency


  A measure of how much energy going into a system is used usefully, calculated as useful energy out / total energy in
• Insulation reduces heat loss from buildings
• Energy sources


  Where we harness energy from, including finite (non-renewable) and renewable sources
• Forces


  Pushes or pulls, can be contact or non-contact
• Vectors


  Representations of forces showing direction and magnitude
• Resultant force


  The single force that has the same effect as two or more forces acting on an object
• Balanced forces


  Forces that add up to zero, meaning the object will not accelerate
• 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
• Work done


  Energy transferred by a force, calculated as force x distance moved
• Hooke's Law


  Force = spring constant x extension, for elastic objects
• Elastic potential energy


  Calculated as 1/2 x spring constant x extension^2
• Moment


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


  Force per unit area, calculated as force / area
• Gas pressure


  Due to collisions of gas particles with surfaces, increased by adding more gas, reducing volume, or raising temperature
• Electricity is the flow of charge (e.g. 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)
• 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, which carry 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 which move through the wires

  3. Movement of charge is called current, flows from positive to negative terminal

  4. Electrons' energy converted to light and heat in the bulb

  5. Electrons pushed back to the battery to be refilled with energy
• Charge


  Measured in coulombs (C), dealt with in 'kums' (large numbers) rather than individual electrons
• Potential difference (PD) / Voltage

  Measure of how much energy is transferred per 'kum' of electrons, in volts (V)