Re: [Phys-l] Energy Question Negative Reps.

[Brian Whatcott <betwys1@sbcglobal.net>]

At 12:36 PM 1/12/2007, Scott Goelzer, you wrote:
> ///
> How much work is done during one repetition of a weightlifting exercise?
> Keeping it simple, let's say a 1000 N barbell is bench pressed 0.5 m
> up and then down at roughly constant speed. The bar was replaced on
> the rack with a polite minimum of clanking.
>
> The change in GPE for the bar is simple, it increases 500 J and then
> decreases 500 J.
>
> What energy expenditure does the person make?
///
> Scott

If I arrange a servo positioner to raise and lower stuff, I expect it 
to use similar amounts of energy to lift, to hold stationary, and to 
drop a load in a controlled fashion.

If I examine an elevator's power consumption, I expect to see it 
using more when descending than ascending if lightly laden. But 
little or none when stationary - when the brake is applied and the 
lift motor is unpowered.

Muscles provide tension when contracting, so pushing and pulling may 
require opposed muscle groups - not for slow descents though I don't think.


Brian Whatcott    Altus OK    Eureka!