Torque is calculated based on the lever arm, which is the perpendicular distance from the axis of rotation to the point where a force is applied. A longer lever arm results in a greater torque. An example calculates the torque on a bicep muscle attached 5 cm from the elbow joint, based on different forces applied. A second example calculates the net torque on two connected wheels from two 50N forces, based on the wheels' radii serving as lever arms. The document concludes by assigning homework problems related to torque calculations.

1. Section 8.4
Torque

2. Torque
 How do I calculate torque?

3. Torque
 How do we cause a rotational motion?
 Apply a force
 The position and direction of the force
make a difference

4. Lever Arm
 Lever Arm: The perpendicular
distance from the axis of rotation to
the point the force is applied

5. Lever Arm
 The
longer the
better

6. Relationships


7. Lever Arm
 FA: = Distance
from hinge to
knob
 FD = zero
 FC: trig

8. Determining Torque Equation


9. Torque Equation


10. 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.

11. 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.

12. Example
 Two 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.

13. Homework
 Read Section 8.4
 Do Problems # 22 – 26, page 220