# Conversion between mass units

I am enrolled in a course related to physics, and converting between mass units is so tricky for me. I always treat in my work only in SI units and maybe MKS units, at level of weights, I find it easy.

But what about the mass conversion between these units:

• kg
• kgf.s^2/m

The first I see is that kg comes from N, and kgf.s^2/m comes from kgf, doesn't it? I don't understand, how to convert, for example 50 kg to ()kgf.s^2/m; I couldn't affect it by gravity because they are mass units, not weight-mass conversion anymore.

This is my notes from my class, to get the right units of frequency:

Stiffness   Mass        Frequency


I have always chose the third row to calculate; but maybe in the exam it could come in other units; and I want to understand it.

I don't know if this is so basic that I have to know, but don't get it.

• I don't know who your instructor is, but he needs to be aware that there are no such units as kgf. If you are in college, and past the drop date, good luck. – David White Oct 5 '18 at 16:37
• As you comment and suggest, I always work with SI units; but I am afraid of the test about this, because I don’t understand how to convert. And, as I posted another question, I am unable to continue after the relation of mass units. – Isai Oct 5 '18 at 16:41

You said that kg comes from N, that's wrong, the value of the kilogram is different to the value of de N (Newton). If you want to calculate the Newtons of a force being applied to a mass you must use F=m*a. Kilograms is the mass and a is the acceleration. As an illustration, LET'S USE earth's gravity to calculate the force that you receive according to your mass. Let's say you have a mass of 50kg, and the gravity (acceleration) on earth is 9.8m/s^2. The force in Newton will be F = 50 * 9,8. And Newton in its formal definition is kg·m·s-2.
• Thank you so much; but, how to convert 50 kg to ()kgf.s^2/m? Furthermore, when I mentioned that kg comes from N, I meant that is a conversion from weight in N to kg. The first question please, or kgs-s^2/m is not mass unit? – Isai Oct 5 '18 at 9:09
• I thought like you, but I didn't ask in class about it, because I thought that I figured it later. But, when you want to convert weight in kgf to mass, you have to divide it by gravity acceleration in our case, and the units will be kgf-s^2/m, isn't? – Isai Oct 5 '18 at 9:20