mudzm4 - Muddy Card Responses Lecture M4 Lot's of mud on...

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Muddy Card Responses Lecture M4 Lot's of mud on the last PRS question. We will go over this on Monday. The question was designed to make you think before I go over the material . You should also look at the lecture notes for lecture M4, which gives the explanations for the three types of problem that were referred to in the question. The explanation is provided in the notes On the PRS question the roller provides a vertical force. Since there's a vertical component applied at that point, does this force change at all? Or do we treat it like a snapshot of forces?. This is an important question. The answer is that that the forces (applied forces and reactions from supports) acting at a point add up (parallelogram rule in 2-D, vector addition in 3-D) and could be replaced by a single resultant force (and moment if appropriate). In the interests of being methodical in drawing free body diagrams (i.e. "FBD's" - to clarify someone elses question) it is usually advisable to keep the forces separate at this stage in the analysis process. Why in the PRS question could we take moments when we said that pin supports could not support moment reactions? (several people asked variations on this) This is another important point. Although pins (and rollers) cannot provide a pure moment reaction on their own, the reaction forces that they apply do exert moments about other points. You might
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mudzm4 - Muddy Card Responses Lecture M4 Lot's of mud on...

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