Physics

• What are the seven stores of energy?

  Gravitational, nuclear, kinetic, thermal, elastic, magnetic, and chemical
• What does it mean when we say that energy is "dissipated"?

  It means that energy has spread out, usually to the thermal store of the surroundings
• Describe what is meant by an open system.

  An open system is one where external forces act and energy can be dissipated
• Describe what is meant by a closed system.

  A closed system is one where no external forces act and no energy is dissipated
• What are the units of energy?

  Joules, J
• What does the law of conservation of energy state?

  Energy cannot be created or destroyed, only shifted between stores; the total amount of energy is always the same
• What is a system in physics?

  A system is an object or a group of objects
• What force do you do work against when you lift an object onto a shelf?

  You do work against gravity
• What force do you do work against when you push an object across a rough surface?

  You do work against friction
• What force do you do work against when you push the opposite poles of two magnets together?

  You do work against the magnetic force between the magnets
• What is meant by the term power?

  Power is the rate of energy transfer or the rate of work done
• What are the units of power?

  Watts, W
• What is the equation for calculating power?

  Power = energy transferred ÷
• One watt is the same as what?

  One Joule per second
• What is meant by the term efficiency?

  Efficiency is the fraction of the total energy that is useful
• What is the equation for efficiency, in terms of power?

  Efficiency = \frac{\text{Useful power}}{\text{Total power}}
• What are the units of efficiency?

  Efficiency has no units, because it is a ratio
• What happens to energy stores when a ball is thrown upwards?

  • Gravitational store increases
  • Kinetic store decreases
• What happens to energy stores when a piece of coal is burnt?

  • Chemical store of coal decreases
  • Thermal store increases
• What happens to energy stores when a car uses its brakes to slow down?

  • Kinetic store decreases
  • Thermal store of brakes increases
• What happens to energy stores when you drop an object that doesn't bounce?

  • Kinetic store decreases during impact with the floor
  • Thermal store of the floor increases
• What happens to energy stores when a car accelerates with a constant force?

  • Kinetic store of car increases
  • Chemical store of fuel or battery decreases
• What happens to energy stores when two magnets with opposite poles are held near to each other and released?

  • Magnetic store of the magnets decreases
  • Kinetic store of the magnets increases