Energy Resources Geothermal –Thermal (Heat under the earth) –Thermal (boil water) –Mechanical or Kinetic (turn turbines) –Electrical
Questions Which energy resource does not boil water? Which energy resource does not turn turbines? Which energy resource does not rely on the sun?
Questions Which energy resources are renewable? Which energy resources are non- renewable? Which energy resource is the best? Why?
Power Work done per unit time Energy per unit time P = work/time = energy / time Units –Joules per second, Js -1 –Watt, W
Example A motor-driven lift carries 24 bricks to the top of a 3 m wall. If each brick weighs 10 N and takes 15 s to get to the top, how much is the power output of the motor? If the motor has a power rating of 1000 W, how long will it take to lift 100 bricks?
Efficiency Describes how much of the energy supplied is used than wasted. Efficiency = useful output power ÷ input power –Output energy ÷ input energy –No units –May be expressed in percentage
Example A block is dragged up a slope with a force of 80 N. The block weighs 100 N and the slope is 20 m long and 10 m high. Calculate the efficiency of the work done.