1. Engineering Mechanics Lecture 3 5/10, Friday 4-5am

2. Tendency of Force to Rotate a Body Two effects of force: 1)Move a body in the direction of its application 2)Rotate a body around an axis.

3. Moment Arm Tendency of the force to rotate a body Is proportional to F and d d: perpendicular distance from the axis to the line of force action

4. Right-Hand Rule Moment in the direction of thumb Fingers curl in the direction of the tendency to rotate

5. Sign of Moment (2D Convention) Plus sign (+): counter clockwise Minus sign (-): clockwise

6. Many-Particle Interactions 1 2 f 21 f 13 3 f 12 f 31 f 23 f 32 F3F3 F1F1 For an N particles system, in equilibrium

7. Many-Particle Interactions For an N particles system, in equilibrium Can you prove: ? Therefore: Need Newton’s 3 rd law Newton’s 1st law:

8. Many-Particle System For a N-particle system, in equilibrium