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Torque. hand. A Comparison. Which of the following do you think is easier to hold in place?. 1 kg. 1 kg. 1 m. 1 m. Why would one be easier than the other? They are the same weight. hand. 1 kg. 1 m. F g. F hand. hand. What is Really Happening?.
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hand A Comparison Which of the following do you think is easier to hold in place? 1 kg 1 kg 1 m 1 m Why would one be easier than the other? They are the same weight. hand
1 kg 1 m Fg Fhand hand What is Really Happening? For the first object, there are only two forces acting on it to keep it at rest. Here the object is simply trying to fall downward.
With the second object you still have only two forces. In this case, the object will try to twist around the hand if it is not allowed to fall. Fhand This twisting effort is called a torque. hand torque Fg What is Really Happening? (part 2) 1 m 1 kg In this case, it is harder to hold still because you are fighting two things-- the gravitational force and its torque.
t = F * r What is Torque? • Torque is a force’s ability to rotate an object. • The symbol for torque is the Greek letter t • 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
Lever arm for Fg = 1 m Lever arm for Fhand= 0 m 1 kg 1 m Pivot Point = hand location Fg Fhand hand Fg is parallel to the lever arm, so it produces no torque
Fhand Fg does have a lever arm, and is not parallel to that lever arm. q = 90O So it does produce a torque around the hand. hand t = 98Nm t = (98N) * (1m) Fg t = 98Nm Clockwise Lever arm for Fg = 1 m Lever arm for Fhand= 0 m Fhand has no lever arm so it produces no torque around the hand Pivot Point = hand location 1 m 1 kg t = F * r
q = + q = - 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
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. • tnet = tcounterclockwise + tclockwise • Remember C.C.W. = + and C.W. = -