Expert: Richard J. Raridon - 2/23/2004

Question
Hi,

I agree that tension is a force. However, could you elaborate why in general, it is a vector quantity? If it is indeed a vector quantity, is there such thing as a "negative tension" exerting a push on a suspending object? Do you have any clues of why my particular textbook ignored the direction of the tension?

Thanks.

-Jeff

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Followup To
Question -
Hello,

I just got my Grade 12 math test back today and got into an argument with an algebra teacher whether tension of two strings, used to suspend an object, is a VECTOR or SCALAR quantity.

The question in the test specifically asked for the "tensions" of the two strings used to suspend an object  -- not the magnitude and direction of the tensions -- just "tensions". I did so by finding out the magnitude only and got it right. However, I lost a mark for not stating the direction.

Of all the examples we did in-class, including examples mentioned in the algebra textbook that we used, stated indirectly that tension was a SCALAR quantity - no direction. I was going to show this to the teacher but he said tension is strictly a vector quantity, and rudely ignored my second request to get into the conversation by saying "goodbye" in front of my face.

So the question still remains: is tension a vector or scalar quantity? I hope you can bring this argument to a closure.

Many thanks for your help.

-Jeff
Answer -
Tension is a force, and therefore, a vector

Answer
A vector consists of a magnitude and a direction.  If you agree that a tension is a force then there's no question about it being a vector.  Think about a ball hanging on a string.  There's a tension in the string that is equal to the weight of the ball.  Weight down, tension up.   If you look at the forces in the trusses of a bridge, there are some tensive forces and some compressive forces (what you might call negative tension).  
Many textbooks have deficiencies. Don't believe everything you read.