Torque & Normals: Why Do We Ignore Normals?

[Offlinedoctor]

Hi,

I'm struggling to understand why we never consider normals when doing torque questions?

One on the top of my head is a hand pushing a bar, 'x' metres away' from the pivot joint. From the worked examples, there is only one torque (the hand), but how come we never consider the normal forces involved? It gets more confusing when I think about applying torque to people on planks, how come when some people are standing we never take into account their normals when applying torque?

 

[SteamKing]

Hi,

I'm struggling to understand why we never consider normals when doing torque questions?

Perhaps you should review the definition of torque:

http://en.wikipedia.org/wiki/Torque

One on the top of my head is a hand pushing a bar, 'x' metres away' from the pivot joint. From the worked examples, there is only one torque (the hand), but how come we never consider the normal forces involved? It gets more confusing when I think about applying torque to people on planks, how come when some people are standing we never take into account their normals when applying torque?

Which 'normal forces' are you talking about? The definition of torque explicitly deals with normal forces acting perpendicular to a moment arm.

 

[jaydnul]

If you have a force acting with both horizontal and vertical components, then the tangent component will be used to calculate the torque. The "normal" component is only used if you have friction at the hinge.