How is coal extracted?
How do Humans use it?
What are the benefits?

coal can be extracted from the earth either by surface mining or underground mining. Once coal has been extracted, it can be used directly (for heating and industrial processes) or to fuel power plants for electricity. If coal is less than 61 meters (200 feet) underground, it can be extracted through surface mining.

Explanation:

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.