6. The track was tilted at 30 degrees, and masses were added in small increments to the hanger until the block (wooden side) stopped moving down. 7. More mass was added to the hanger until reaching the critical point, 97.1 g, at which the block moved up the slope. The kinetic friction coefficients and the static friction coefficients for all trials were calculated with the equation Ffr (max) = μs/kFN μs/k=Ffr/FN(mg) Analysis: Figure 1: Maximum Frictional Force vs Normal Force The graph is of the maximum frictional force of the block and track plotted against the normal force of the block or the weight of the block. The slope of the graph represents the friction coefficient, so the
friction coefficient is proportional to the normal force (N=mg on a horizontal surface). Table 1. shows the various calculations done in the lab involving friction. Row: The coefficient of static friction μs= Ffr/FN(mg) (1) Mass needed to move the block in grams divided by the mass of the block ex. 55.1 g/ 123.29 g = 0.4469 Row: The coefficient of kinetic frictional μk= Ffr/FN(mg) (2) Mass needed to move the block with adding a push in grams divided by the mass of the block ex. 60.1 g/173.29 g = 0.3468 Discussion: The static friction coefficients of all trials are larger than the kinetic friction coefficients because there is a greater force needed to make the block start sliding than the force to pull it with a constant speed. This is a logical outcome since the theory about static friction states that the static friction force is larger than the kinetic friction force. The friction coefficients (both static and kinetic) of soft surfaces like felt are smaller than the coefficients of wood on wood (see table I). This in understandable because friction varies with texture between the surfaces in contact, and felt has a smoother texture than wood. The friction coefficients of the block turned on its side along the track is smaller than the friction coefficient of the wooden block (greater area) in contact with the wooden track, which is actually incorrect because the coefficient of friction is independent of the area of contact. Friction depends only slightly on the shape and size of the object in question. Since the recorded results do not match with the empirical law it can be inferred that there were other forces or errors in the lab. When gradually adding
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