# Hi This is a really trivial comment in my notes but for some

Hi

This is a really trivial comment in my notes but for some reason I'm not seeing it...

The following image demonstrates the perpendicular distance from an origin to the line of action of the force given as x*sin(x,F). So the moment, M = f*x*sin(x,F) which I understand.

But why is it sin? Why not cos or tan? I understand trig, I just can't see how this is working. Maybe because of the positioning of the angle?

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rude man
Homework Helper
Gold Member

Hi

This is a really trivial comment in my notes but for some reason I'm not seeing it...

The following image demonstrates the perpendicular distance from an origin to the line of action of the force given as x*sin(x,F). So the moment, M = f*x*sin(x,F) which I understand.

But why is it sin? Why not cos or tan? I understand trig, I just can't see how this is working. Maybe because of the positioning of the angle?

The vector formula for moment is τ = r x F. In your notation, r = x and F = F.

The magnitude of r x F is |r|*|F|*sinθ where θ is the angle between r and F. This is strictly a mathematical definition.

Apologies

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