Revise: Power and Efficiency
Power and its units, mechanical and energy efficiency, the stretching of a coiled spring, and sources of energy.
P = W/t; power is the RATE of energy transfer, measured in watts.
6000 J of work in 12 s gives 500 W.
Ξ· = (useful output/total input) Γ 100%; no real machine reaches 100%.
350 J useful from 500 J input gives 70% efficiency.
F = kx: force is proportional to extension, within the elastic limit.
A 250 N/m spring stretches 0.06 m under a 15 N force.
E = Β½kxΒ² gives the energy stored in a stretched or compressed spring.
A 300 N/m spring compressed 0.08 m stores 0.96 J.
Non-renewable (fossil fuels, finite) vs. renewable (solar, wind, hydro β replenish naturally).
Solar farms draw on continuously renewed sunlight, unlike a coal plant's finite fuel.