Energy

• What is a system in the context of energy stores?


  A system is an object or group of objects.
• How does the way energy is stored change when a system changes?


  The way energy is stored also changes when a system changes.
• What happens to the kinetic energy of a ball when it rolls and hits a wall?


  • The system is the moving ball.
  • When it hits the wall, some of the kinetic energy is transferred as sound.
• What occurs to the kinetic energy of a vehicle when it slows down?


  • The system is the moving vehicle.
  • Kinetic energy transfers to thermal energy due to friction between wheels and brakes.
• What is the formula for calculating kinetic energy?


  $E_k =$$\frac{1}{2} mv^2$
• What do the variables in the kinetic energy formula represent?

  m is mass in kilograms, v is speed in meters per second, and Ek is kinetic energy in joules.
• What type of energy is stored in a spring when it is stretched?

  Elastic potential energy.
• What is the formula for elastic potential energy?


  $E_e =$$\frac{1}{2} ke^2$
• What do the variables in the elastic potential energy formula represent?

  Ee is elastic potential energy in joules, k is the spring constant in N/m, and e is extension in meters.
• What is the formula for gravitational potential energy?


  $E_p =$$mgh$
• What do the variables in the gravitational potential energy formula represent?

  Ep is gravitational potential energy in joules, m is mass in kg, g is gravitational field strength in N/kg, and h is height in meters.
• What is specific heat capacity?

  It is the energy required to raise the temperature of 1 kg of a substance by 1°C or 1K.
• What is the formula for calculating thermal energy change?

  $E =$$mc\Delta T$
• What do the variables in the thermal energy change formula represent?


  ∆E is change in thermal energy in joules, m is mass in kg, c is specific heat capacity in J/kg°C, and ∆T is temperature change in °C.
• How is power defined?


  Power is the rate at which energy is transferred or the rate at which work is done.
• What is the formula for calculating power?

  $P =$$\frac{E}{t} =$$\frac{W}{t}$
• What do the variables in the power formula represent?

  P is power in watts, E is energy transferred in joules, t is time in seconds, and W is work done in joules.
• What does an energy transfer of 1 joule per second equal in terms of power?

  It equals a power of 1 watt.
• How can the power of two motors A and B be compared?

  • The motor that can do the same work faster is more powerful.
  • This is because energy is transferred at a faster rate.
• What are the ways energy can be transferred?

  • Energy can be transferred usefully, stored, or dissipated.
  • Energy cannot be created or destroyed.
• What happens to energy during system changes?

  • Energy is dissipated, stored in less useful ways.
  • This energy is often described as being 'wasted.'
• How can energy waste be reduced?

  • Lubrication (e.g., oil in a motor reduces friction).
  • Thermal insulation (e.g., double glazing reduces thermal energy loss).
• What is thermal conductivity?


  It is the ability of a material to allow heat to travel through it.
• How does thermal conductivity affect energy transfer in buildings?

  The higher the thermal conductivity, the higher the rate of energy transfer by conduction across the material.
• What happens to the rate of cooling in buildings with thick walls and low thermal conductivity?

  • The rate of cooling is low.
  • If walls are thin metal sheets, heat would be lost very quickly.
• What is efficiency in the context of energy systems?

  Efficiency is the ratio of useful work done to the energy supplied, often expressed as a percentage.
• What is the formula for calculating efficiency?

  $\text{efficiency} =$$\frac{\text{useful energy output}}{\text{total energy input}} =$$\frac{\text{useful power output}}{\text{total power input}}$
• How can the efficiency of a system be increased?

  • By reducing waste output (e.g., lubrication, thermal insulation).
  • By recycling waste output (e.g., absorbing thermal waste and recycling as input energy).
• What are the main non-renewable energy sources?

  • Fossil Fuels (coal, oil, gas)
  • Nuclear Fuel
• What are the main renewable energy sources?

  • Biofuel
  • Wind
  • Hydro-electricity
  • Geothermal
  • Tidal
  • Solar
  • Water waves
• What is the difference between renewable and non-renewable energy?

  Renewable energy can be replenished as it is used, while non-renewable energy cannot.
• Why is renewable energy becoming more important?


  Due to the finite lifetime of fossil fuels, the development of renewable energy has become more important.
• What are some reliability issues with renewable energy sources?

  • Solar energy doesn’t work in bad weather or at night.
  • Wind energy is only intermittent.
• What are the main uses of energy?

  • Transport
  • Electricity generation
  • Heating
• What are some environmental impacts of energy extraction and use?

  • Fossil fuels involve destroying landscapes.
  • Wind turbines can be considered an eyesore.
  • Fossil fuels release harmful emissions.
  • Solar and wind create electricity with no emissions.
• How did the industrial revolution affect energy use?

  • Fossil fuels became an important source of energy due to ease of mining and high energy output.
  • Renewable energy has become more suitable only recently due to technological advancements.
• What challenges are associated with increasing energy resource use?

  • Increasing pressure to meet public power demands.
  • Difficulty in solving environmental issues due to political, social, ethical, and economic considerations.