MOMENT OF A FORCE ABOUT A LINE

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• Lecture 11
• MOMENT OF A FORCE ABOUT A LINE

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MOMENT OF A FORCE ABOUT A LINE

• The moment of a force with respect to
  a line OB can be determined by
• (1)calculate the moment about pt. O.
• (2)resolve into components along line
  OB(parallel) and perpendicular to line OB.

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MOMENT OF A FORCE ABOUT A LINE

• where is the unit vector in the n direction
  along line OB. The coefficient of indicates
  that has the same sense as .

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MOMENT OF A FORCE ABOUT A LINE
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EXAMPLE 1
z

• Problem
• Determine the scalar component of the moment at
  point
• O about OC and at point D about DE.

500
250
O
y
c
E
300
x
D
A
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EXAMPLE 1

• Solution
• (a)moment at pt. O about OC.
• express in Cartesian vector form
• the unit vector

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EXAMPLE 1

• The position vector,

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EXAMPLE 1

• (b) moment at pt. D about line DE
• the unit vector,
• the position vector

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EXAMPLE 2

• Problem
• Determine the scalar component of the moment
• at point O about the line OB

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EXAMPLE 2

• Solution
• Express in Cartesian vector from.
• The unit vector

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EXAMPLE 2

• The position vector

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• ADDITIONAL MATERIAL
• Read Section 4.5
• Problem Section 4
• 51, 59, 63, 65