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

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 C: Mechanics expects students to know that mechanical energy can be dissipated as thermal energy or sound by nonconservative forces.