Holding a Heavy Book
Classical Mechanics
Level
2
A person requires several calories of energy to hold a heavy book for one hour. How is this energy spent?
Heat in the muscles
Doing work on the block
Resisting gravitational force
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1 solution
When we hold a book, the book is not moving. We can find the work done on the book by W = F ⋅ d . Since the book is not moving, no work is being done on the book. Yet, we require energy and feel tired after holding it for a long period of time. So where is this energy being spent?
The answer lies in the mechanism of how we hold the book. In order to keep holding the book, our muscles keep contracting and relaxing, which requires energy and is then emitted as heat. On the other hand, if we keep the same book on a table, then the table can hold the book for without spending energy for as much time as we want.