1. Torque

2. A Comparison Which of the following do you think is easier to hold in place? 1 m 1 kg 1 m 1 kg hand Why would one be easier than the other? They are the same weight.

3. What is Really Happening? For the first object, there are only two forces acting on it to keep it at rest. 1 m 1 kg hand FgFg F hand Here the object is simply trying to fall downward.

4. What is Really Happening? (part 2) 1 m 1 kg hand With the second object you still have only two forces. FgFg F hand In this case, it is harder to hold still because you are fighting two things-- the gravitational force and its torque. In this case, the object will try to twist around the hand if it is not allowed to fall. This twisting effort is called a torque. torque

5. What is Torque?  Torque is a force’s ability to rotate an object.  The symbol for torque is the Greek letter   There are 3 factors that influence the torque around a point: Magnitude of the force The distance the force is from the pivot point The angle the force makes with the lever arm.  The unit for torque is a Newton-Meter (Nm) This is not the same a Joule  = F * r

6. 1 m 1 kg hand FgFg F hand Pivot Point = hand location Lever arm for F g = 1 m Lever arm for F hand = 0 m F g is parallel to the lever arm, so it produces no torque

7. 1 m 1 kg hand FgFg F hand Lever arm for F g = 1 m Lever arm for F hand = 0 m Pivot Point = hand location F hand has no lever arm so it produces no torque around the hand  = 90 O F g does have a lever arm, and is not parallel to that lever arm.  = (98N) * (1m)  = 98Nm Clockwise  = 98Nm So it does produce a torque around the hand.  = F * r

8. Directions of Torques  Since torques try to rotate objects into a circle they have only two possible directions. Clockwise (often considered negative) Counterclockwise (often considered positive)  The signs follow the standard for measuring angles  = +  = -

9. Net Torques  Just like multiple forces acting on an object sum up into one Net (resultant) Force. Multiple torques sum up to one net torque.   net =  counterclockwise +  clockwise Remember C.C.W. = + and C.W. = -