Apparent Weight

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Apparent Weight
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Static and Kinetic Friction

• Jeff is trying in vain to push a large freezer of
  elk meat across his garage floor. The mass of
  freezer, including contents, is 250 kg. The
  coefficient of static friction between the
  freezer and the floor is 0.80. Jeff is pushing
  with a horizontal force of 1000 N but the freezer
  will not budge. What is the magnitude of the
  frictional force acting on the freezer? Explain
  your reasoning.

fk mkN fsmax msN
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Sir Isaac Newton (1642-1727)
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Newtons Law of Gravity
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Cavendish, Henry (1731-1810)

• Measured G in 1798

G 6.67 x 10-11 Nm2/kg2
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What is the force between my head and a book?
F 2 x 10-10 N
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What is the force between my head and a book?
1,2
F 2 x 10-10 N
or??
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What is the force between the Earth and a book?
Wearth,book Mbook (9.8 N/kg)
Mearth 5.98 x 1024 kg
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Storey Musgravem 80 kg
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Whats his mass?
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Whats his weight?
648 N !
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Apollo 17
Earth as seen from the Moon
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What is the correct orbit of the space shuttle?
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What is the correct orbit of the space shuttle?
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At the surface of the Earth
Wearth,Story MStory (9.8 N/kg)
(80 kg) (9.8 N/kg) 784 N
rearth 4000 miles
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400 miles above the surface
Wearth,Story MStory (8.1 N/kg)
(80 kg) (8.1 N/kg) 648 N
rearth 4000 miles
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Which force does the scale read?
Apparent Weight
True Weight
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Apparent weight

• measured as the reading of the scale
• equal to the normal force of the scale on your
  feet
• equal to weight for a0

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Elevator
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Elevator
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Elevator
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Problem

• You are riding down in an elevator carrying a 20
  kg package in your arms. As the elevator gets to
  your floor, it slows with an acceleration of 2
  m/s/s. What is the apparent weight of the
  package while the elevator is slowing?

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Elevator
How large should the normal force be?
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Elevator
How large should the normal force be?
a 9.8 m/s/s down
Apparently
Weightless??
WEP
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