Torque

1
Torque

• Torque
• From Latin word torquere
• to twist
• Force with leverage.
• Torques result in rotation
• Defined as the force times the lever arm.

2
Torque

• Lever arm The perpendicular distance from the
  axis of rotation to the line along which the
  force acts.

• Force in Newtons lever arm in meters
• Units Nm (or mN)

3
Torque

• Torque
• Torque F x d
• Force and lever arm must be ?

4
Torque
Torque
F ?
F
Lever Arm
Torque F ? x d Force and lever arm must be
? Take component of F ? to lever arm
5
Torque
F
Torque
F ?
?
Lever Arm
Torque F ? x d F ? F sin ? so . . . .
Torque (?) Fd(sin ?)
6
Torque

• Is there a direction to torque?
• Keeping things simple
• Counter clockwise positive
• Clockwise - negative

7
d
Torque (?) Fd(sin ?)
Fig 8.15b, p.245
Slide 7
8
Equilibrium Revisited
Box on table What are the sum of the forces?
In Equilibrium
9
Is below in equilibrium? Dont know for sure.
Fig 8.12, p.243
Slide 9
10
Is below in equilibrium?
Sum your forces
Ignore the weight of the beam (to keep things
simple)
But is there acceleration? No linear acceleration.
11
But how about rotational accel?
We dont know.
We must sum the torques
If the sum of the Torques is zero, then it is in
rotational equilibrium
Fig 8.12, p.243
Slide 11
12
Put some numbers here
If the man weighs 600N and is 2 m from O
What does the girl weigh if she is 4m from o?
13
Put some numbers here
If the man weighs 600N and is 2 m from O
What does the girl weigh if she is 4m from o?
Solving for F2 300N
Fig 8.12, p.243
Slide 13
14
In which figure is there the least amount of
torque (F is equal in all three figures)?
Fig 8.14, p.244
Slide 14
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Fig 8.p250, p.250
Slide 15
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Fig 8.26, p.251
Slide 16
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Fig 8.Q1, p.266
Slide 17
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Fig 8.MC2, p.267
Slide 18
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Fig 8.P70, p.274
Slide 19
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Fig 8.P75, p.274
Slide 20
21
The uniform beam (whose weight acts at its
center) is completely at rest. The scale reads
90N. What is the weight of the mass on the left
and the weight of the beam?
Fig 8.P76, p.275
Slide 21
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Sum your forces then torques
Two unknowns so you must use Torques
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Fig 8.P77, p.275
Slide 24
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Fig 8.P78, p.275
Slide 25
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Fig 8.P84, p.275
Slide 26
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Fig 8.P85, p.276
Slide 27
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Fig 8.P87, p.276
Slide 28
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