Re: [Phys-L] 9th grade energy resource projects

[Bernard Cleyet <bernard@cleyet.org>]

On 2014, Dec 13, , at 09:41, Dan Beeker <debeeker@comcast.net> wrote:

> This is exactly the reason one would want to have a bicycle powered generator demonstration. Most everyone thinks it is a good idea until you actually get on one and find out how little practical utility such a thing has. It takes a lot of effort (I was going to say work : ) to run even a 100 watt load for any reasonable length of time. 


What’s wrong w/ “work”?   Here’s where I think the two meanings are co-incident.   And  100 w is v. ~ 1 seventh of a horse power.  Sooo no surprise.

bc  thinks an 80kg person in no match to a 500kg horse.    

Furthermore:  


When considering human-powered equipment, a healthy human can produce about 1.2 hp briefly (see orders of magnitude) and sustain about 0.1 hp indefinitely; trained athletes can manage up to about 2.5 hp briefly[15] and 0.3 hp for a period of several hours.  

The typical person is NOT trained, especially here in the US.  


Horsepower - Wikipedia, the free encyclopedia  

http://en.wikipedia.org/wiki/Horsepower#History_of_the_unit  

Remember an hp is > 700 w.