3.4 Conservation of Energy

Describe the energies present in a system.

• A system composed of only a single object can only have kinetic energy.
• A system that contains objects that interact via conservative forces or that can change its shape reversibly may have both kinetic and potential energies.

Describe the behavior of a system using conservation of mechanical energy principles.

• Mechanical energy is the sum of a system’s kinetic and potential energies.
• Any change to a type of energy within a system must be balanced by an equivalent change of other types of energies within the system or by a transfer of energy between the system and its surroundings.
• A system may be selected so that the total energy of that system is constant.
• If the total energy of a system changes, that change will be equivalent to the energy transferred into or out of the system.

Describe how the selection of a system determines whether the energy of that system changes.

• Energy is conserved in all interactions.
• If the work done on a selected system is zero and there are no nonconservative interactions within the system, the total mechanical energy of the system is constant.
• If the work done on a selected system is nonzero, energy is transferred between the system and the environment. BOUNDARY STATEMENT AP Physics 1 expects students to know that mechanical energy can be dissipated as thermal energy or sound by nonconservative forces. AP Physics 1: Algebra-Based Course and Exam Description Work, Energy, and Power UNIT 3 TOPIC 3.5 Power | AP Physics 1: Algebra-Based Course and Exam Description