12 Static Equilibrium and Elasticity

• Conditions for Equilibrium

• The Center of Gravity

• Some Examples of Static Equilibrium

• Omit sections 4, 5, 6.

• Stress and Strain

• Hk: 19, 21, 23, 31, 33, 41.

Conditions for Equilibrium

Center of Gravity, cg

• center of gravity: the average location of weight

Q: A 70kg student lies along a board with a fulcrum at one end and a scale 2.0m away at the other end. The top of his head is directly above the fulcrum. When he is on the board as described the scale reading is 250N more than when he is off the board. Where is the cg of the student?

12-6Stability of Rotational

Equilibrium

12-7Indeterminate Problems

Omit

12-5Static Equilibrium in an

Accelerated Frame

12-4Couples

End

normal force on wheel 0

12-8Stress and Strain

Q: What % shortening of a 50cm diameter concrete pillar occurs when a 20 000 kg truck is balanced on top of it? What is the maximum load in kg?

A cube 50cm per side suffers shear strain of 1% when a shear force of 10 000N is applied along two opposite faces. What is the shear modulus of this material?

Summary