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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