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Unformatted text preview: DISCUSSION PROBLEM [5.1]: DISCUSSION PROBLEM [5.1]: ... answer ... The “friction” equation The “friction” equation r
r
f = µN is not a vector equation. Why not? r
r
f = µN r
r
is not a vector equation because f is not parallel to N . 1 DISCUSSION PROBLEM [5.2]: ... answer ... FBA DISCUSSION PROBLEM [5.2]: FAB FGA = f A FGB = f B A B Identify the forces acting on each person. FAB and FBA
are an A/R pair. Two people (A and B) are tugging at each other. By ∴ FAB = FBA .
Note that the (frictional) forces are one part of A/R Newton’s 3rd law the force that A applies on B is equal pairs also, i.e., FGA = FAG and FGB = FBG to the force that B applies on A . How come one of them Since FAB and FBA cancel each other the result can pull the other off their feet? What is the most depends on the frictional forces FGA and FGB. A B important factor? (Hint: consider only the forces acting
on each person.) • If FGA > FGB then A wins!
• If FGB > FGA then B wins!
If f = µ s N for both people then the person with greater
mass should win! Note that if there’s no friction (e.g.,
on ice) no one wins! 2 ...
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 Spring '08
 Guzman
 Physics, Friction

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