Question

To combat wasteful habits, we often speak of “conserving energy,” by which we mean turning off lights and hot energy,” by which we mean turning off lights and hot water when they are not being used, and keeping thermostats at a moderate level. In this chapter, we also speak of “energy conservation.” Distinguish between these two Usages.

Answer 1

In the first instance you are minimizing your flow of energy from your energy source, for example your fuel tank.
The meaning of conservation of energy in physics is that in a physical process the total amount of energy does not change. However it may become quite useless to you. For example a rock on top of a cliff has potential energy compared to when it is on the ground below. That potential may be used with a pulley for example to pull a weight up to the top of the cliff as the rock falls. However if the rock just falls by itself, its potential energy is turned to kinetic energy on the way down, then just heats up the ground (mechanical energy goes to heat energy) when it hits. The same amount of energy is still there, but it is quite useless to you now since it just heated up the ground a little.