## A Conversation for Torque or Moment

### F dot d?

26199 Started conversation Apr 11, 2002

Hmm. That can't be a dot product... you'd want a cross product, vector d from the origin and not the parallel distance, and vector F... so... er... is it just supposed to be another notation for multiplication?

Or am I missing something?

### F dot d?

Trendy upbeat really catchy name, like Clint, or Brian, no, Alfy would be good. Or John. Posted Apr 11, 2002

yes

### F dot d?

TwickersMan Posted Apr 11, 2002

I think it's just a bog standard multiply that any cheap calculator can manage. Ingore what's in the brackets, and notice they used the '*', which seems to have replaced 'x' for people using calculator simulators on thier PCs (I wonder why?)

### F dot d?

furtim - Zaphodista Sympathiser Posted Apr 11, 2002

Torque is F cross d when torque is being expressed as a vector but F dot d as a scalar. This works because the F being considered in the dot-product version is only the component of the force acting perpendicular to the lever arm, yielding T = F*sin(theta) dot d when you take F to be the magnitude of the overall force. F*sin(thera) dot d = F cross d

### F dot d?

26199 Posted Apr 11, 2002

Hmm, but surely F is perpendicular to d and so the dot product is zero, and what you actually want is just a straight multiplication...

### F dot d?

Ion the Naysayer Posted May 21, 2002

It is intended to be straight multiplication. I guess I should edit more carefully next time before submitting an article for review

Oops.

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### F dot d?

- 1: 26199 (Apr 11, 2002)
- 2: Trendy upbeat really catchy name, like Clint, or Brian, no, Alfy would be good. Or John. (Apr 11, 2002)
- 3: 26199 (Apr 11, 2002)
- 4: TwickersMan (Apr 11, 2002)
- 5: furtim - Zaphodista Sympathiser (Apr 11, 2002)
- 6: furtim - Zaphodista Sympathiser (Apr 11, 2002)
- 7: 26199 (Apr 11, 2002)
- 8: furtim - Zaphodista Sympathiser (Apr 12, 2002)
- 9: Ion the Naysayer (May 21, 2002)

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