The discussion clarifies the treatment of normal forces in free-body diagrams involving torque. When analyzing a board with weights on either side of a pivot, only external forces, such as weight forces and pivot support forces, are considered. Normal forces from the weights are classified as internal forces and are therefore excluded from the initial analysis. However, a separate free-body diagram of the board can include these normal forces, yielding consistent results in torque calculations.
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In the free body diagram of the board and weight system, you look at external forces only , the weight forces and pivot support forces. The normal forces of the weights are internal forces and excluded. If you wish , however, you can draw a free body of the board alone , then the forces external to the board become the pivot force and the normal force of the 2 objects acting on the board, and get the same result.Gabe805 said:I was just curious as why, when drawing a free-body diagram of a board about a pivot with weight on either side of the pivot, we do not consider the corresponding normal forces to those weights(using torque considerations). This question was already asked in another post but was asked a little less clearly.