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Hi I am trying to learn the concepts of angular momentum but I don't understand why in the formula for torque the radius from the line of action of the force is regarded as a vector surely distance is only a scalar so why is the cross product used?

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    $\begingroup$ actually that is not distance it is the position vector for the point of application. $\endgroup$
    – Anonymous
    Commented Nov 14, 2020 at 10:47

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That is not distance, It is position vector.

There is no concept that for a vector quantity always a cross product of two vectors is taken. In physics some quantities are even given direction so that you can take their cross product. Cross product is a tool not a property.

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$${\bf \tau = r \times F }$$ Here "r" is actually the position vector(also called radius vector) i.e. the vector from the axis of rotation to where the force is applied.
enter image description here

Its magnitude actually does equal the distance from the axis, but it's still a vector(having both magnitude and direction, as shown in the figure).

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  • $\begingroup$ Thanks this was helpful $\endgroup$ Commented Nov 14, 2020 at 11:23

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