PHYS.7.C

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The student is expected to apply the concept of conservation of energy using the work-energy theorem, energy diagrams, and energy transformation equations, including transformations between kinetic, potential, and thermal energy;
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Knowledge and Skills Statement

Science concepts. The student knows that changes occur within a physical system and applies the laws of conservation of energy and momentum.

A system is often defined as the device used to do work and the objects it comes in contact with, such as a car moving people along a road. When the car gets its electricity from photovoltaic cells, energy flows into the system from the sun. As the car moves, mechanical energy is transformed into thermal energy through work done by friction in the motor and on the road. The heat flows out of the system into the car's environment. At times, it may appear that energy is not conserved. This occurs when energy either enters or leaves the system without being measured.

Most models of energy transformation do not account for the thermal energy produced by friction, which is generally transferred out of the system as heat. An energy diagram can represent a roller coaster's relative amounts of kinetic and potential energy as it travels along a track.

When performing energy calculations, the following connected concepts may be important to remember:

  • Unknown quantities can be calculated from known information.
  • Work is a form of energy.
  • The object's mass does not change, is irrelevant to transformation calculations, and can be removed from both sides of the equation.

the energy caused by the motion of objects or particles within a system

energy that is stored in an object due to its position relative to some zero position in a specified frame of reference; can be stored in an electromagnetic or gravitational field

regularly interacting or interdependent group of items forming a unified whole

a phenomenon of energy that measures the random motion (kinetic energy) of particles (vibrations in solids or free motion in a gas) in a substance

Research

Solbes, Jordi, Jenaro Guisasola, and Francisco Tarín. "Teaching Energy Conservation as a Unifying Principle in Physics." Journal of Science Education and Technology 18, no. 3 (2009): 265-274. https://doi.org/10.1007/s10956-009-9149-3

Summary:  In this work the authors present the design and assessment of a teaching sequence aimed at introducing the principle of energy conservation at post-compulsory secondary school level (16–18 year olds). The proposal is based on the result of research into teaching-learning difficulties and on the analysis of the physics framework. Evidence is shown that this teaching sequence, together with the methodology used in the classroom, may result in students having a better grasp of the principle of energy conservation.