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.
  • Kinetic energy is transferred as sound when it hits the wall.
• 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 kg, v is speed in m/s, and $E_k$ 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?

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

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

  $E_p$ is gravitational potential energy in joules, m is mass in kg, g is gravitational field strength in N/kg, and h is height in m.
• 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 $\Delta T$ 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 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 it mean when energy is described as being 'wasted'?

  It means energy is dissipated and stored in less useful ways during system changes.
• 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)
• How does thermal conductivity affect energy transfer?

  The higher the thermal conductivity, the easier heat travels through the material, increasing energy transfer rate.
• What is the impact of wall thickness and thermal conductivity on cooling rates in buildings?

  • Thick walls with low thermal conductivity result in low cooling rates.
  • Thin metal sheets lead to rapid heat loss.
• What is efficiency in the context of energy use?

  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?

  • Reducing waste output (e.g., lubrication, thermal insulation)
  • Recycling waste output (e.g., absorbing thermal waste)
• What are the main non-renewable energy sources?

  Fossil fuels (coal, oil, gas) and nuclear fuel.
• What are the main renewable energy sources?

  Biofuel, wind, hydro-electricity, geothermal, tidal, solar, and 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 has renewable energy become more important recently?

  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, and wind energy is intermittent.
• What are the main uses of energy?

  Transport, electricity generation, and heating.
• What are the environmental impacts of energy extraction and use?

  • Fossil fuel extraction destroys landscapes.
  • Wind turbines can be considered an eyesore.
  • Fossil fuels release harmful emissions.
  • Solar and wind create electricity with no emissions.
• What patterns and trends have influenced energy use over time?

  • Fossil fuels became important during the industrial revolution due to easy mining and high energy output.
  • Renewable energy has become more suitable due to technological advancements.
  • Increasing public power demands complicate solving environmental issues.