torque definition

[theonlytycrane]

Using the equation rFsin(theta) is easy enough. But the previous definition (r cross F) confuses me. The cross product should result in a vector orthogonal to r and F. But in my see-saw drawing, the see-saw should torque down in the plane of r and F. The cross product makes it seems as though the see-saw would be torquing into or out of the page.

Am I missing something here?

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[aldol16]

The direction of torque is not the same thing as the direction of motion. The direction of torque is actually pointing along the axis of rotation and is given by a right-hand rule.

 

[7331poas]

The torque is into the page yes?


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[aldol16]

Yeah, if you're crossing r with F.

 

[theonlytycrane]

The direction of torque is not the same thing as the direction of motion. The direction of torque is actually pointing along the axis of rotation and is given by a right-hand rule.

Does into or out of the page give any useful information about the torque? I guess in both cases the direction is along the axis of rotation, and is just a mathematical result from the definition of torque as a cross product.

 

[aldol16]

It certainly gives some physical information about the torque - since torque is intimately related to angular momentum. However, I believe that would be outside the scope of the MCAT.