[Phys-L] Negative work done by a person

[Savinainen Antti <antti.savinainen@kuopio.fi>]

Hi,

a contributor to Phys-L, Carl Mungan, has published a nice paper in TPT: "Negative work done by a person".
<http://scitation.aip.org/content/aapt/journal/tpt/53/4/10.1119/1.4914563>

This is a question I have thought about as well and occasionally addressed it with my students.
A tangential question: *How* is gravitational potential energy stored in the gravitational field? 

A Finnish physics textbook answered that it is stored as mass: the mass of the gravitational field increases when
a person lifts, say, a book. Do you find this explanation plausible?

Regards,

Antti Savinainen, PhD
Finland


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