is conserved
Energy is conserved in a closed system. That is, if you add up all the energy of an object s at one time it will equal all the energy of said object s at a later time. A closed system is a system where no energy is transferred in or out. The total energy of the universe is a constant i. e. it does not change . The problems below do not consider the situation of energy transfer called work . So friction and other sources where energy leaves the system are not present. Thus, one simply adds up all the potential energy and kinetic energy before and sets it equal to the addition of the total potential energy and kinetic energy after .