FORCES

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FORCES
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Force

• the action of one body on another
• may be the result of direct contact
• contact may not be necessary
• gravity
• magnetic field
• electric field

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Force Systems

• Two force systems are said to be equivalent if
  they produce the same external effect when
  applied in turn to a rigid body.
• Two systems that are equivalent are called
  replacements for each other.

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Force Systems

• The resultant of a force system is the simplest
  equivalent system to which the original system
  will reduce.
• The process of reducing a force system to a
  simpler equivalent is called reduction.
• The process of expanding a force system into a
  less simple equivalent system is called
  resolution.

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Characteristics of a Force

• Characteristics the properties necessary to
  describe the force
• Characteristics
• magnitude amount or size
• direction orientation and sense point of
  application
• point of application point in space where the
  force is applied

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Scalar

• magnitude only
• examples
• temperature
• time
• mass
• area

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Vector

• magnitude
• direction (orientation and sense)
• obeys parallelogram law of addition
• examples
• force
• velocity
• momentum

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Vector

• notations, vector A

hand written
hand written
type set
hand written (this course)
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Vector (cont.)
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Parallelogram Law of Addition
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Types of Vectors

• Bound (fixed) vector
• specific magnitude and direction
• line of action passes through a unique point in
  space
• point of application a fixed point on its line of
  action.
• Sliding vector
• specific magnitude and direction
• line of action passes through a unique point in
  space
• point of application can be anywhere along its
  line of action.

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Types of Vectors (cont.)

• Free vector
• specific magnitude and direction
• line of action does not pass through a unique
  point in space
• example a free vector can act along any line
  parallel to its line of action.

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Principal of transmissibility

• For rigid bodies and particles
• The external effect of a force on the body is the
  same for all points of application of the force
  along its line of action.

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Resultant of two concurrent forces

• concurrent forces ? lines of action intersect
• Resultant, R, is the vector sum of the two forces
  F1 F2.
• To add according to the parallelogram law
• slide the vectors along their lines of action
  until the two have a common origin
• sum R is the vector forming the diagonal of the
  parallelogram.
• Use Laws of Sines, Cosines to solve triangle
  problem.

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END