Energy Changes in a system

• How is a system defined in physics?

  A system is defined as an object or group of objects.
• Why is defining a system important in physics?

  It narrows the parameters to focus only on what is relevant to the situation being observed.
• What happens when a system is in equilibrium?

  Nothing changes and so nothing happens.
• What occurs when there is a change in a system?

  Things happen, and energy is transferred.
• What happens to an apple when the table it is on is removed?

  The apple will fall, and energy is transferred as it falls.

  
• In what units is energy measured?

  Energy is measured in joules (J).
• What are the three types of thermodynamic systems?

  A thermodynamic system can be isolated, closed, or open.

  
• What is an open system?

  An open system allows the exchange of energy and matter to or from its surroundings.

  
• What is a closed system?

  A closed system can exchange energy but not matter to or from its surroundings.

  
• What is an isolated system?

  An isolated system does not allow the transfer of matter or energy to or from its surroundings.

  
• What are the different energy stores in physics?

  • Kinetic: Energy of moving objects
  • Gravitational: Energy gained when lifted in a gravitational field
  • Elastic: Energy stored when stretched, squashed, or bent
  • Magnetic: Energy in magnetic materials interacting
  • Electrostatic: Energy in charged objects interacting
  • Chemical: Energy transferred in chemical reactions
  • Nuclear: Energy released during nuclear reactions
  • Thermal: Energy related to temperature of an object
• What does the principle of conservation of energy state?

  Energy cannot be created or destroyed; it can only be transferred from one store to another.
• What is the total amount of energy in a closed system?

  The total amount of energy is constant.
• What are the pathways for energy transfer?

  • Mechanically
  • Electrically
  • By heating
  • By radiation
• What is mechanical working in energy transfer?

  Mechanical working occurs when a force acts on an object, such as pulling or pushing.
• What is electrical working in energy transfer?

  Electrical working occurs when a charge moves through a potential difference, such as current.
• How is energy transferred by heating?

  Energy is transferred from a hotter object to a colder one.
• What is energy transfer by radiation?

  Energy is transferred by electromagnetic waves, such as visible light.
• What is an example of energy transfer in everyday life?

  A hot coffee heating up cold hands is an example of energy transfer.

  
• Describe the energy transfers when a battery powers a torch.

  1. Energy is transferred from the chemical store of the battery.
  2. Energy is transferred to the thermal store of the bulb.
  3. Energy is transferred electrically through the circuit.

  
• Describe the energy transfers when a ball falls.

  1. Energy is transferred from the gravitational potential store as the ball falls.
  2. Energy is transferred to the kinetic store as the ball moves.
  3. The transfer pathway is mechanical due to the force of gravity.
• What is the formula for kinetic energy?

  E = \frac{1}{2} m v^2
• What does kinetic energy depend on?

  Kinetic energy depends on the mass and speed of an object.
• How do you calculate the kinetic energy of an object with mass 1200 kg moving at 27 m/s?

  E = \frac{1}{2} \times 1200 \times (27)^2 = 440000 \text{ J}
• What is gravitational potential energy defined as?

  Gravitational potential energy is the energy an object has due to its height in a gravitational field.
• What happens to gravitational potential energy when an object is lifted?

  Energy is transferred to its gravitational potential store.
• What happens to gravitational potential energy when an object falls?

  Energy is transferred away from its gravitational potential store.
• What is the formula for gravitational potential energy?

  E = m \times g \times h

  
• What is the approximate gravitational field strength on Earth?

  Approximately 9.8 N/kg.
• How does gravitational field strength vary on different celestial bodies?

  It is easier to lift a mass on the Moon than on Earth and harder on gas giants like Jupiter.
• How do you calculate the gravitational potential energy of a man of mass 70 kg climbing 3 m with a gravitational field strength of 9.8 N/kg?

  \Delta E = 70 \times 9.8 \times 3
• What is the process of energy transfer when boiling water in an electric kettle?

  1. Energy is transferred electrically from the mains to the kettle.
  2. Energy is transferred to the thermal store of the heating element.
  3. Energy is transferred by heating to the thermal store of the water.

  
• What are some common situations where energy transfers occur?

  • An object projected upwards
  • A moving object hitting an obstacle
  • A vehicle speeding up or slowing down
  • Water being brought to a boil in an electric kettle
• Why is it easier to lift a mass on the Moon than on Earth?

  Because the gravitational field strength on the Moon is less than on Earth.
• How does the gravitational field strength on gas giants compare to that on Earth?

  The gravitational field strength on gas giants like Jupiter and Saturn is greater than on Earth.

  
• What is the approximate value of gravitational field strength on Earth?

  1. 8 N/kg
• How do you calculate the gravitational potential energy transferred to a man climbing stairs?

  Use the equation ΔE = mgΔh.
• If a man of mass 70 kg climbs a height of 3 m, what is the energy transferred to his gravitational potential energy store?

  ΔE = 2058 J.
• What is the formula for elastic potential energy?

  E = \frac{1}{2} k e^2.
• What does elastic potential energy represent in an object?

  It is the energy stored in an elastic object when work is done on it.