Conservation of Energy

Conservation of Energy

Energy Stores and Transfers

• Energy Definition: Energy is essential for all actions and interactions in a system.
• Energy Stores: Think of energy stores like buckets that hold energy.
  • Kinetic Energy: Energy of a moving object.
  • Thermal Energy: Energy within an object due to its temperature; hotter objects contain more thermal energy.
  • Chemical Energy: Energy released during chemical reactions (e.g., food, fuel).
  • Gravitational Potential Energy: Energy stored in objects due to their position in a gravitational field.
  • Elastic Potential Energy: Energy in stretched or compressed objects (e.g., springs).
  • Electrostatic Energy: Energy stored when electric charges interact.
  • Magnetic Energy: Energy related to magnetic fields and interactions (e.g., magnets).
  • Nuclear Energy: Energy stored in atomic nuclei, released during nuclear reactions.

Energy Transfers

o System Definition: A single object or a group of objects under examination.

• Closed System: No energy enters or leaves; total energy remains constant (net change is zero).
• Example of Closed System: A sealed thermos flask maintains the temperature of soup as no energy is lost to surroundings.

Key Learning Objectives:

• Explain energy transfers in a closed system.
• Analyze changes in energy storage across various scenarios (e.g., object projected upwards, a moving object hitting an obstacle).
• Define conservation of energy and provide examples of energy dissipation in systems.
• Recognize inefficiencies in mechanical processes that can lead to heating and energy loss.
• Interpret energy transfer diagrams.

Methods of Energy Transfer:

1. Mechanically: Energy transferred through force (e.g., pushing, pulling).
2. Electrically: Movement of charge (current) through a potential difference.
3. By Heating: Transfer from hot to cold objects (e.g., heating water).
4. By Radiation: Transfer through waves (e.g., sunlight reaching Earth).

Work Done:

• Work Definition: Energy transferred via force over a distance; can be mechanical or electrical.
  • Example Scenarios:
  • Work done to throw a ball: transfers chemical energy from the person to kinetic energy of arm and ball, then to gravitational potential energy of the ball.

Conservation of Energy Principle:

• Energy cannot be created or destroyed but can be transformed from one store to another.
• Formula for kinetic energy: KE = \frac{1}{2} m v^2
• Example: Ball rolling up a slope converts kinetic energy to gravitational potential energy.
• Energy output can be useful or wasted (dissipated).

Useful Energy Stores and Dissipation:

• Not all energy transferred is useful; energy may become thermal energy of surroundings (wasted energy).
• Efficiency of Devices: The less energy wasted, the more efficient the device. Efficiency can be improved by reducing waste.

Energy Transfer Diagrams:

• Diagrams use boxes for energy stores and arrows for transfers.
• Example: Diagram representing a ball thrown upwards accounting for air resistance and energy transfers.

Practice Questions:

1. List eight forms of energy store.
2. Define net change in energy for a closed system.
3. State the conservation of energy principle.
4. Describe energy transfers during various physical processes (arrows, boiling water, battery operation).
5. Explain differences in energy measurements using specific scenarios (e.g., ball’s potential vs kinetic energy).