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



I’ve recently had some students from back in the 80’s remind me of our HS Physics lab that had them (voluntarily) running up five flights of stairs. Measuring the vertical displacement, their weight and the elapsed time. Calculating their average Power during the exercise.

VERY rarely could a student break One Horsepower.

These students used both their arms AND their legs to propel themselves upward. (Just a s horses do)

It was important for them to grab the railing to pull up the stairs AND to pull inward while swinging themselves around (inward) on each landing. Lots of good lessons to be recalled as we got to Circular Motion etc.

Some have been able impress their current employers by doing ‘off the cuff’ Units Analysis when others have fumbled.

(Take Care of your Units - and your Units will Take Care of YOU ! ! !)



On Dec 13, 2014, at 5:07 PM, Bernard Cleyet <bernard@cleyet.org> wrote:


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.
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