P1 Conservation and Dissipation of Energy

• What is the definition of a closed system?

  A system where no energy can escape
• What is kinetic energy?

  Energy an object has because it is moving
• What is gravitational potential energy?

  Energy due to an object's height above ground
• What is elastic potential energy?

  Energy an elastic object has when stretched
• What is thermal energy?

  Energy due to an object's temperature
• What is chemical energy?

  Energy transferred by chemical reactions
• What is nuclear energy?

  Energy stored in the nucleus of an atom
• What is magnetic energy?

  Energy a magnetic object has near a magnet
• What is electrostatic energy?

  Energy a charged object has near another charged object
• What are the four ways energy can be transferred?

  • Heating
  • Waves
  • Electric current
  • Mechanically (by forces)
• What happens in a closed system?

  The total energy never changes
• How is work done defined?

  Energy transferred when a force moves an object
• What is the unit for energy?

  Joules (J)
• What is one joule of work?

  Work done when 1 N moves 1 m
• Describe the energy transfer when a moving car slows down.

  Energy transfers from kinetic to thermal store
• Describe the energy transfer in an electric kettle.

  Electric current transfers energy to heating element
• Describe the energy transfer when a ball is fired using an elastic band.

  Energy transfers from elastic to kinetic store
• Describe the energy transfer in a battery-powered toy car.

  Energy transfers electrically from battery to kinetic store
• Describe the energy transfer when a falling apple hits the ground.

  Energy transfers from kinetic store to thermal store
• What unit represents one joule transferred per second?

  Watt (W)
• What does it mean if a motor is 30% efficient?

  30% of energy is usefully transferred
• What is the equation for calculating work done?

  • Work done (J) = Force (N) × Distance (m)
• What is the equation for gravitational potential energy?

  • Gravitational potential energy (J) = mass (kg) × gravitational field strength (N/kg) × height (m)
  • Ep = mgh
• What is the equation for kinetic energy?

  • Kinetic energy (J) = 0.5 × mass (kg) × (speed)² (m/s)
  • Ek = $\frac{1}{2}mv^2$
• What is the equation for elastic potential energy?

  • Elastic potential energy (J) = 0.5 × spring constant (N/m) × (extension)² (m)
  • Ee = $\frac{1}{2}ke^2$
• What is the equation for power?

  • Power (W) = Energy transferred (J) / Time (s)
  • P = $\frac{E}{t}$
• What is the equation for efficiency?

  • Efficiency = Useful output energy transfer (J) / Total input energy transfer (J)
  • Efficiency = Useful power output (W) / Total power input (W)
• What happens to energy in a system?

  • Energy can be transferred, stored, or dissipated
  • Energy cannot be created or destroyed
• What are methods to reduce energy dissipation?

  • Lubrication reduces friction
  • Streamlining reduces air resistance
  • Thermal insulation reduces heat loss
• What is the relationship between useful and dissipated energy?

  • Some energy is always dissipated
  • All energy eventually transfers to thermal store