# Help with power calculation please.

by billbarlow
Tags: calculation, power
 P: 4 I have designed and built a device that harnesses centrifugal force.The power output is in the form of 2 x 10mm steel rod "pistons" that move up and down a distance of 15mm. I have measured the weight these pistons can lift to be 122lbs when the device is operated @ 4000rpm. Each piston moves up and down once per revolution. I have calculated this to be an output of 1.45 hp. ( 15mm=.049125ft x 66.666 times per second=3.27496 ft x 122lbs = 399.54 lbs/ft/sec = .7264hp x 2 = 1.45hp. Can people please either confirm my calculations are correct or point out my error(s). If I am correct,given that the device is solely powered by a 500w electric drill, am I able to claim the impossible?
Mentor
P: 40,947
 Quote by billbarlow I have designed and built a device that harnesses centrifugal force.The power output is in the form of 2 x 10mm steel rod "pistons" that move up and down a distance of 15mm. I have measured the weight these pistons can lift to be 122lbs when the device is operated @ 4000rpm. Each piston moves up and down once per revolution. I have calculated this to be an output of 1.45 hp. ( 15mm=.049125ft x 66.666 times per second=3.27496 ft x 122lbs = 399.54 lbs/ft/sec = .7264hp x 2 = 1.45hp. Can people please either confirm my calculations are correct or point out my error(s). If I am correct,given that the device is solely powered by a 500w electric drill, am I able to claim the impossible?
If you are putting 500W in, then you are not getting more than that amount of power delivered. Can you re-do your calcs in MKS units to double-check?
 P: 4 Sorry dont know what MKS units are. 500w = .67hp though??
 Mentor P: 40,947 Help with power calculation please. MKS = meters, kilograms, seconds.
Thanks
PF Gold
P: 12,132
 Quote by billbarlow I have designed and built a device that harnesses centrifugal force.The power output is in the form of 2 x 10mm steel rod "pistons" that move up and down a distance of 15mm. I have measured the weight these pistons can lift to be 122lbs when the device is operated @ 4000rpm. Each piston moves up and down once per revolution. I have calculated this to be an output of 1.45 hp. ( 15mm=.049125ft x 66.666 times per second=3.27496 ft x 122lbs = 399.54 lbs/ft/sec = .7264hp x 2 = 1.45hp. Can people please either confirm my calculations are correct or point out my error(s). If I am correct,given that the device is solely powered by a 500w electric drill, am I able to claim the impossible?
You have not defined the output power - or measured it. Moving weights up and down does not imply doing net work. Consider a spinning wheel. One side goes up and then it goes down the other side. No energy is used up at all (except for a bit of friction). Nothing is wrong with Physics. Perpetual motion does not exist.
 P: 4 Thank you Sophiecentaur. Is there a way I can measure the power output? Any help much appreciated.