What kind of energy/effort is used to power a crane?

i probably sound like an idiot asking this question :P
is it electricity? fossil fuel burning involved? pulleys? how does the pulley work? any human power involved?
specifically, how is it stupid to lift a chair that can be lifted by a person, with a crane?

2 Responses to “What kind of energy/effort is used to power a crane?”

  1. leesy  on August 22nd, 2011

    A crane is a pulley and using simple machines like wedges, screws, pulleys etc. takes less work.

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  2. biire2u  on August 22nd, 2011

    Most cranes are diesel engine powered hydraulics and hydraulic motor. So that would be fossil fuel.

    Some cranes use pulleys to magnify the total lifting capacity. A pulley magnifies work by exchanging distance for lifting power. For example, to lift a 10 ton weight 20 feet in the air, if you put four pulleys in there so that 80 feet of cable would have to be pulled up , then it would only take 1/4 the amount of power to lift that 10 tons (2.5 ton lifting force would lift it)

    Look at any links or wikipedia for how compound pulleys work.

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