energy (physics)

• What is a system in physics?

  An object or group of objects
• How does energy storage change in a system?

  It changes when the system changes
• What happens to kinetic energy when a ball hits a wall?

  • Kinetic energy is transferred as sound
  • Some energy is dissipated
• What occurs to a vehicle's kinetic energy when it slows down?

  • Kinetic energy transfers to thermal energy
  • Caused by friction between wheels and brakes
• What is the formula for kinetic energy?

  Ek = ½mv²
• What do the variables in the kinetic energy formula represent?

  m is mass, v is speed
• What type of energy is stored in a stretched spring?

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

  EPE = ½k x e²
• What do the variables in the elastic potential energy formula represent?

  k is spring constant, x is extension
• What is the formula for gravitational potential

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

  m is mass, g is gravitational field strength, h is height
• What is specific heat capacity?

  Energy to raise 1kg by 1°C
• What is the formula for calculating thermal energy change?

  E = mcΔT
• What do the variables in the thermal energy change formula represent?

  E is energy, m is mass, c is specific heat capacity, ΔT is temperature change
• How is power defined in physics?

  Rate at which energy is transferred
• What is the formula for power?

  P = E/t = W/t
• What does an energy transfer of 1 joule per second equal?

  1 watt of power
• How can you determine which motor is more powerful?

  The one that does work faster
• What are the ways energy can be transferred?

  • Usefully
  • Stored
  • Dissipated
  • Cannot be created or destroyed
• What happens to energy in system changes?

  It is dissipated and stored less usefully
• How can energy waste be reduced?

  • Lubrication reduces friction
  • Thermal insulation minimizes heat loss
• What is thermal conductivity?

  Rate of heat transfer through a material
• How does wall thickness affect cooling rate?

  Thicker walls reduce cooling rate
• What is efficiency in a system?

  Ratio of useful work to energy supplied
• How is efficiency expressed?

  Often as a percentage
• How can efficiency be increased?

  By reducing waste output and recycling
• What are the main energy sources?

  • Non-renewable: fossil fuels, nuclear fuel
  • Renewable: biofuel, wind, hydro-electricity, geothermal, tidal, solar, water waves
• What is renewable energy?

  Energy that can be replenished as used