On Thu, 22 Aug 2019 14:02:19 -0700 (PDT),
wrote:

On Thursday, 22 August 2019 21:34:05 UTC+1, Bill Wright wrote:
How come it needs much less effort to hold an electric sander against
the work than it does to do the work manually?

Because it's easier to hold something still than to move it.

If you turned the sander off and rubbed the wood against it, the sander wouldn't be using any energy.

It's a bit like cycling - easier than walking, but actually less efficient in a purely energy sense because there's the additional weight of the bicylce to move.

Owain
Mass.

If the sander were made of polystyrene you would be more in agreement
with Newton.

AB