11/4 Torque in Equilibrium

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11/4 Torque in Equilibrium

• Today Finding Torque, ? Your Lab
• HW 11/4 HW Handout Extended FBD and Torque due
  Thur 11/7 (None due Wed)
• Exam 3 Thursday, 11/14
• Example problem

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Torque
Max torque
0 torque
Medium torque
Pivot (axis)
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Perpendicular force method
F? ?
F sin ?
?
Torque ? F? ? distance from axis (r)
? r F sin ?
4
Lever arm method
? r F sin ?
F? ?
F sin ?
?
l r sin ?
? F l
F r sin ?
90
?
90
r
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Torque

• Depends on
• Size of the force
• Distance from the axis (you choose axis!!!)
• Angle of the force with respect to a line drawn
  to the axis from location the force is applied.
• Must draw an extended FBD!!

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CM in Lab
Where is the center of mass of the bar?
F1
O
F3
equilibrium
F2
F4 mbarg but where is it applied?
D
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Example
Find the tension in the angled string and the
force (magnitude and direction) the pivot puts on
the bar.
1kg
?
30
2m
3kg
?CW ?CCW ? 0
W(1) T2(2) T1,?(2)
10 60 T1,?(2)
T1,? 35N
T1,? T1sin30
T1 70N
Note FBD not to scale
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Example
Find the tension in the angled string and the
force (magnitude and direction) the pivot puts on
the bar.
T1 70N
1kg
?
30
2m
3kg
?CW ?CCW ? 0
FUp FDown a 0
Can use either concept to get pivot force of 61N
at 4.7 above horizontal toward the right.
Will need to pick a new axis to use torque.