Chapt.8: Newton

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Chapt.8 Newtons Third Law

• 8.1 Interacting Systems
• 8.2 Identifying Action/Reaction pairs
• 8.3 Newtons Third Law
• 8.4 Ropes and Pulleys
• 8.5 Examples of Interacting-System problems

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Stop to think 8.1 P213Stop to think
8.2 P215Stop to think 8.3 P218Stop to think
8.4 P220Stop to think 8.5 P223Stop to think
8.6 P227

• Example 8.3 P215
• Example 8.5 P219
• Example 8.6 P222
• Example 8.8 P224
• Example 8.9 P226

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Interacting system
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Systems and the environment
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Newtons third Law

• Every force occurs as one member of an
  action/reaction pair of corces
• The two members of an action/reaction pair act on
  two different objects
• The two members of an action/reaction pair are
  equal in magnitude but opposite in direction

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Stop to think 8.3 Boxes A and B are sliding to
the right across a frictionless table. The hand H
is slowing them down. The mass of A is larger
than the bass of B.. Rank in order , from largest
to smallest, the horizontal forces on A, B, and
H.
a. F B on H F H on B F A on B F Bon A b. F
B on H F H on B gt F A on B F Bon A c. F B on
H F H on B lt F A on B F Bon A d. F H on B F
H on A gt F A on B
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Atwood machine
Neglect rope and pulleys mass
(1) Compare a1 an a2 (2) Compare T1 and T2 If m2
gtm1 (3) Draw the free body diagrams
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More diagrams (Massless String)
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Questions (1) if there is friction force between
A and table, what is equation for A
(2) For what condition, B is at rest
(3) when is the weight of B equal
tension T
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P. 8.8
Notice if there is an acceleration, F(G on c) is
not equal F(T on C)
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Write Newtons second law for boy and package

• For boy
• For Package notice the x direction is along the
• Ramp