Lecture - Static Equilibrium and Elasticity

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In the Law of Motions, one necessary condition for equilibrium is that the

net force acting on an object (particle) must be zero.

For an extended object (cannot be modeled as particles) a second

condition must be satisfied –

the net torque on the extended object.

Consider a single force F acting on a rigid object – Fig. 12.1.

The effect of F depends on the location of P

(point of application). If r is the position vector of 

of this point relative to O, the torque:

Its cross product vector. Use right-hand rule. Torque

direction is out of the page.

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In the xy plane:

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(CG)

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EXAMPLE:

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SOLUTION:

(A)

(B)

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EXERCISE VI:

1.

Figure 12.11

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2.