What explains the fact that no machine is 100 percent efficient?

How many moles of air are there in a human lung with a volume of 2.4 l at stp? explain your answer

Americium-241 undergoes fission to produce three neutrons per fission event. if a neutron-absorbing material is mixed in with this sample so that the rate of neutron production drops down to 1.8 neutrons per fission event, which will be effective at achieving a critical mass? check all that apply. remove a deflective shield surrounding the sample. remove absorbent material mixed in with the sample. compress the sample of americium-241.

Why are people not able to skip a dive to the deepest part of the ocean