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I’m taking Introductions to Physics book. In the book on the chapter “Physics & Mathematics” there was one question where we were supposed to find the magnitude of work done from given vectors Force & Displacement.

Using Dot product I successfully calculated the number part of Magnitude and wrote $Nm$ as unit.

Then I looked at the answer and it was written: $4.0 N-m$ or $4.0 J$.

I understand Joules but how is we have - instead of multiplication?

We can’t add difrent quantities, is that why we use - as multiplication operator. If yes why did we even needed it? What purpose does it justify?

Qmechanic
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Prabhas Kumar
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1 Answers1

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It's a typesetting convention by that author or book publisher. I prefer your way of writing it, but you should not be surprised to see the other way used occasionally.

In the US, the N-m version is found more often in engineering texts (and usually in old ones rather than new ones) than in physics texts, but usage may vary around the world.

Of course you should also usually prefer to express energy or work in joules (J). If you see units of Nm or N-m, it usually denotes torque rather than energy or work.

The Photon
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    Just in case it isn't clear, the point is that the "-" in "N-m" is a hyphen not a minus sign. It does not mean Newtons minus metres. – John Rennie Oct 30 '23 at 08:21