Section 1 review
Static equilibrium means that both the net force is zero in all directions and the net torque is zero around any center. Torque is the “twisting” equivalent of force. Torque is force times distance, which has SI units of newton-meters and has units of pound-feet in the English system. The torque created by a force is the magnitude of the force multiplied by the lever arm, which is the perpendicular distance from the center to the line of action of the force. The general procedure for solving static problems is to create a free-body diagram, resolve all forces into components, and then apply the equilibrium conditions for both forces and torques. Read the text aloud
torque, line of action, lever arm, fulcrum, lever

F =0
τ=0
τ=r×F

Review problems and questions

Free body diagram of a mass held by two chains
  1. Which of the following gives the correct force equilibrium equations for the problem on the right?
    1. TxF = 0, Tymg = 0
    2. TyF = 0, Txmg = 0
    3. TFmg = 0
    4. T + F + mg = 0 Read the text aloud Show
What is the torque created by this force?
  1. What is the torque created by the force drawn in the diagram?
    1. 25 N m
    2. −25 N m
    3. 100 N m
    4. −100 N m Read the text aloud Show
Two masses attached to a rod that is held by a single chain
  1. Which of the following equations is a correct statement of rotational equilibrium for the problem on the right?
    1. m1g + m2g + T = 0
    2. m1gd1 + m2gd2 = 0
    3. m1gd1m2gd2 = 0
    4. m1gd1 + m2gd2 + T = 0 Read the text aloud Show

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