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October 1991

Grams of Force

Author Affiliations

Cleveland, Ohio

Arch Ophthalmol. 1991;109(10):1346. doi:10.1001/archopht.1991.01080100026016

To the Editor.  —I compliment Britt et al1 for their excellent photographs and interpretation of the clinical significance of microaerosol formation. In their "Comment" section, I counted five instances in which they used the phrase "g of force." The authors may recall that gram is a unit of mass, not of force.2 Force is measured in dynes (g·cm·s-2) or in newtons (kg·m·s-2), and is the product of mass and acceleration, according to Sir Isaac Newton's second law. For example, a 1-g mass at the surface of the earth is acted on by 1 g times 981 cm·s-2, or 981 dynes, of force, where 981 cm·s-2 is the acceleration due to gravity. To a physicist, the phrase "grams of force" is meaningless. Britt et al may reply that two textbooks on glaucoma3,4 described the scale of Goldmann's applanation tonometer as being calibrated in "grams