Question

why do living beings and machines need energy

Answer 1

they need energy to survive

Answer 2

Living beings--- Every living organism, animals and plants, need a continual supply of energy to perform the processes necessary for reproduction and survival. Machines--- In physics, energy is required for work to be performed. If you have a machine that you want to just sit somewhere, it doesn't need any energy. If you want a machine to actually do something, then it needs energy. In space, a satellite can travel millions of miles without any added energy (just the energy required to set it on its path). In a sense, a form of perpetual motion. On earth, true perpetual motion doesn't exist. If one doesn't want a machine to stop due to friction and other forces, then one must add energy. Hope u like it..