Energy is transferred by heating, radiation, electrical work or mechanical work. The total energy of a closed system is conserved; energy is neither created nor destroyed. Dissipated energy spreads into the surroundings and becomes less useful for the intended purpose. Example: A device receives 100 J and transfers 25 J usefully. Calculate the dissipated energy. 100 − 25 = 75 J. Distinguish the observation from the explanation, and support any judgement with evidence. Distinguish the quantities.