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Units of Measure
Physics
Weight and Mass

How many kilograms are in a newton?

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October 07, 2009 12:09AM

Newtons don't convert directly to kilograms because the Newton is the SI unit of force, and the kilogram is the SI unit of mass.

Mass is different from force or weight, because mass is independent of gravity. Weight is a force and is measured in Newtons and mass is measured in kilograms.

Force = mass x acceleration, F=ma

The confusion comes from the way we often use kilograms as though we are talking about weight, because we are almost always talking about weight on Earth. Your weight would be different on Earth and on the moon, because these places have different strengths of gravity, but your mass would be the same.

A Newton is defined as the force required to accelerate a mass of 1 kilogram at 1 ms-2. (one metre per second per second)

On Earth, where the gravitational acceleration is approximately 9.8ms-2, (9.80665002...ms-2), the weight (the force from the gravity of Earth) of an object with a mass of 1kg is ~9.8N.
a= 9.8ms-2
m=1kg
therefore F= m x a = 9.8N

If an object has a weight on Earth of 1N then it has a mass of ~0.1kg.
a = 9.8ms-2
F = 1N
m = F / a = ~0.1kg