Could you please tell me what the difference between "force" and "mass" here (in relation with cutting) is?

They cut not by sharpness but by force and mass.

Is it correct to say "They cut ... by mass"? There is a physical relationship between "force" and "cutting" but is there any relationship between "mass" and "cutting"?

The fuller text is here:

A few days later Dad came home with the most frightening machine I’ve ever seen. He called it the Shear. At first glance it appeared to be a threeton pair of scissors, and this turned out to be exactly what it was. The blades were made of dense iron, twelve inches thick and five feet across. They cut not by sharpness but by force and mass.They bit down, their great jaws propelled by a heavy piston attached to a large iron wheel. The wheel was animated by a belt and motor, which meant that if something got caught in the machine, it would take anywhere from thirty seconds to a minute to stop the wheel and halt the blades. Up and down they roared, louder than a passing train as they chewed through iron as thick as a man’s arm. The iron wasn’t being cut so much as snapped. Sometimes it would buck, propelling whoever was holding it toward the dull, chomping blades.

Educated by Tara Westover

  • 2
    The meanings of force and mass are their normal definitions of physics. It might be slightly more fluent to say "they were cut by means of force and mass" or "by the force and mass of the blades", but the meaning is the same.
    – stangdon
    Commented May 30, 2018 at 20:17

1 Answer 1


The writer is not a physicist. I interpret the words as intending to create a mental picture.

Force is common usage, referring to the pressure that the machine was able to apply to the blades.

Mass seems to refer to the massiveness of the machine, its very large size and robustness (see Cambridge: massive).

It's saying that the blades didn't have to rely on being sharp to do the cutting. The machine could cut the iron bars just because of how large and strongly made it was, and how much pressure it could apply.

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