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How Does 1 kg Mass and 1 m/s² Acceleration Define a Newton?
Discover the exact SI definition of one newton: the force accelerating a 1 kg mass at 1 m/s². Explore Newton’s second law and why common misconceptions like gravity on 1 kg fail.
Question
Which one of the following statements defines one Newton of force?
A. A Newton is a force of gravity on a 1 kg body.
B. A Newton is a force that gives a 1 kg body an acceleration of 1 m = s2.
C. A Newton is a force of gravity on a 1 g body.
D. A Newton is a force that gives a 1 g body an acceleration of 1 cm/s2.
Answer
B. A Newton is a force that gives a 1 kg body an acceleration of 1 m = s2.
Explanation
The newton (N) is the SI unit of force, precisely defined as the force required to impart an acceleration of one meter per second squared (
1m/s2) to a mass of one kilogram (1kg). This definition stems directly from Newton’s second law of motion, F=ma, where substituting SI base units yields
1N=1kg⋅m/s2. Option A is incorrect because the gravitational force on a 1 kg mass at Earth’s surface is approximately 9.8 N, not 1 N; option C misstates the mass as 1 g; and option D uses non-SI cgs units (1 g and 1 cm/s²), equivalent to only 0.0001 N.