A heavy block, labeled "A", is sitting on a table. On top of that block is a lighter block, labeled "B" as shown in the figure at the right. For the first parts of this problem you are asked to identify the direction of forces in this system under various circumstances. In this problem, we will be looking at the relationships between the various forces in the problem under various circumstances. In order to simplify the equations we write, we will not use our full "who is acting on whom" force notation, but will use the following simplifications. (Note that we have taken for granted that you understood and could use Newton's 3rd law.) • NF→A = F (force of the finger pushing block A) NA+B= NB-A = N (the normal forces acting between the blocks) •NT A = NT (the normal force of the table acting on block A) • FTA = fT (the friction force between block A and the table) • fA+B=fB-A = f (the friction force between the two blocks) • WE AWA (weight of block A) • WE BWB (weight of block B) We then have the seven symbols representing all the forces in the problem: F, NT, N, fT, f, WA, and WB. B A
Suppose we assume that the finger is pushing harder on the blocks now than it did in part (a) but not as hard as it was in the previous section. Which of the other 6 forces change compared to what they were in the previous section? If they do change, do they each get bigger? Smaller? Go to zero?
a) How does N change?
Goes to zero
No change
Gets bigger
Gets smaller
b) How does N_T change?
Goes to zero
No change
Gets bigger
Gets smaller
c) How does f_T change?
Goes to zero
No change
Gets bigger
Gets smaller
d) How does f change?
Goes to zero
No change
Gets bigger
Gets smaller
e) How does W_A change?
Goes to zero
No change
Gets bigger
Gets smaller
f) How does W_B change?
Goes to zero
No change
Gets bigger
Gets smaller
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