1. The Greek letter Tau

5. The Physical Study of Balance
Equilibrium

9. Conditions for equilibrium
Sum of forces is zero Tendency to rotate is zero

10. Torque
the effectiveness of a force in causing rotation on a rigid object also called moment of force

11. Rigid Object vs. Point/Particle Model

12. Prerequisite Observation for 2nd Condition
Which of the following forces will effectively rotate the beam at point O?

13. Prerequisite Observation for 2nd Condition
Which of the following forces will effectively rotate the beam at point O?

14. Prerequisite Observation for 2nd Condition
Which of the following forces will effectively rotate the beam at point O?

15. Prerequisite Observation for 2nd Condition
Which of the following forces will effectively rotate the beam at point O?

16. Factors that determine torque
The amount of force perpendicular to the lever arm.
The distance of the force from the pivot point.

17. Guidelines for Problem Solving
Illustrate all the forces and the lever arm for each.
Torque is the product of force and its distance from the point of rotation.
Force and the lever arm must always be perpendicular.
Establish the point of rotation.
Equate the sum of forces to zero.
Equate the sum of torques to zero.

18. Exercise
A 50.0 N uniform beam, 10.0 m in length, is suspended on a support as shown. If the fulcrum divides the beam into the ratio of 2:3, where should a 6.00 kg object be placed to balance the beam? x

19. Exercise
In a Singkil dance, two men are carrying a princess on a bamboo pole that is 5.00 m long and weighs N. If the princess weighs 425 N and sits 1.50 m from one end, how much weight must each man support?

20. Exercise
(Follow up)
Where should the princess sit so that one man supports her with a force twice that of the other? ?

21. Exercises
Consult page 117 of your book and read Practice Exercise 5.8

22. Rx
lRx
3.5m w Ry f 1m lw

23. Exercises
A uniform 50.0 N ladder rests on a frictionless wall as shown. What minimum coefficient of friction is needed on the ground to prevent it from slipping? 5m 2m

24. Exercises
A uniform aluminum beam 9.00 m long, weighing 300 N, rests symmetrically on two supports 5.00 m apart. A boy weighing 600 N starts at point A and walks toward the right.
From your diagram, how far beyond point B can the boy walk before the beam tips?