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Section 8.4Torque
TorqueHow do I calculate torque?
TorqueHow do we cause a rotational
motion?
Apply a force
The position and direction of the force make a difference
Lever ArmLever Arm: The perpendicular
distance from the axis of rotation to the point the force is applied
Lever ArmThe
longer the better
RelationshipsIf F is constant and r increases, the
amount of angular acceleration increases
Angular acceleration is the product of forces times the lever arm
product is called the moment of the force or torque ()
Lever Arm
FA: = Distance from hinge to knob
FD = zero
FC: trig
Determining Torque EquationTorque:
is the lever arm
Or we can resolve the force into components and say
Torque Equation
is the angle between the force and the line r
Line r is drawn between the axis of rotation and place of force application
Units are m·N
Example
The biceps muscle exerts a vertical force on the lower arm, bent as shown. For each case, calculate the torque about the axis of rotation through the elbow joint, assuming the muscle is attached 5.0 cm from the elbow as shown.
Example
The biceps muscle exerts a vertical force on the lower arm, bent as shown. For each case, calculate the torque about the axis of rotation through the elbow joint, assuming the muscle is attached 5.0 cm from the elbow as shown.
ExampleTwo thin disk-shaped
wheels or rA = 30 cm and rB = 50 cm, are attached to each other on an axle that passes through the center each. Calculate the net torque on this compound wheel due to the two forces shown, each of magnitude 50 N.
HomeworkRead Section 8.4Do Problems # 22 – 26, page 220