Torques and Moments of Force

Objectives:

• Define torque
• Define static equilibrium
• Determine the resultant of two or more torques
• Determine if an object is in static equilibrium when the forces and torques acting on the object are known
• Determine an unknown force or torque acting on an object, if all the other forces and torques acting on the object are known and the object is in static equilibrium
• Define center of gravity

Information from this chapter will be presented in class, without a corresponding powerpoint presentation. If you miss any class period during this chapter, you will need to see a classmate for the missed material, or you can visit me during my office hours.

The Chapter 5 Summary is as follows:

1. Torque (T), or a moment of force, can be described as the turning effect produced by an eccentric force (F). The mathematical description for torque is: T = F × r, where r indicates the moment arm of the force.
2. If you are considering torques about the same axis of rotation, you can algebraically add them, similar to certain forces; counterclockwise torques are represented as positive torques and clockwise torques are represented as negative torques.
3. The sum of the torques about a single axis is called the net moment, or the resultant torque.
4. In order for an object to be in static equilibrium the following equations must be satisfied, indicating in part that the net moment, about all three axes, equals zero:

   ΣF_x = 0; ΣF_y = 0; ΣF_z = 0;

   ΣM_x = 0; ΣM_y = 0; ΣM_z = 0;

5. The center of mass, or center of gravity, is the theoretical location at which the sum of the moments created by the force of gravity equals zero.
6. Stability is the ability of an object to return to equilibrium, after being displaced. Stability is affected by three primary mechanical factors:
   1. The nature of the base of support;
   2. The height of the center of gravity;
   3. The weight of the considered object.

Sample Exam Questions

Sample Exam Questions With Answers