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MECHANICAL ADVANTAGE

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MECHANICAL ADVANTAGE * * * * * * * * * * * * * * * * * * * * * * * * * * Forces we encounter in SAR Simple Machines Mechanical Advantage of Pulley Systems MECHANICAL ... – PowerPoint PPT presentation

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Title: MECHANICAL ADVANTAGE


1
MECHANICAL ADVANTAGE
2
  • Forces we encounter in SAR
  • Simple Machines
  • Mechanical Advantage of Pulley Systems

3
MECHANICAL ADVANTAGE
  • FORCE
  • What is Force
  • What types of Force do we encounter
  • What are the Units of Force

4
MECHANICAL ADVANTAGE
  • What is Force?
  • Force is an external influence that may cause a
    body to accelerate. It may be experienced as a
    lift, a push, or a pull.
  • Force is a vector. All forces will have a
    magnitude and direction.

5
  • Forces we encounter in SAR
  • Forces due to
  • Gravity
  • Friction
  • Impulse
  • Applied Forces

6
  • Gravity
  • g 32.2 ft/sec2 9.8 m/s2
  • F ma
  • F 0.10197 kg x 9.8 m/s2 1Newton (N)
  • A newton is the amount of force required to
    accelerate a body with a mass of one kilogram at
    a rate of one meter per second squared.
  • 1 kN 1,000 N 224.81 lbf

7
  • Gravity Weight
  • 1 kN 224.81 lbf
  • 80kg (0.8 kN 1 kN) for a single load,
  • 200kg (440 lbs 1.95 kN 2 kN) for a rescue
    load
  • 280kg (617 lbs 2.7 kN 3 kN) for a three-man
    load.

8
  • Gravity Weight
  • 1 kN 224.81 lbf
  • 1 Person 1 kN
  • 2 Person 2 kN
  • 3 Person 3 kN

9
  • Gravity Weight
  • The average rescuer can hold or apply a .2 kN
    force with one hand ( 45 lbs)
  • The average rescuer can hold or apply a .4 kN
    force with two hands ( 90 lbs)
  • Hauling an rope hand-over-hand is applying a
    force of 45-50 lbs

10
  • Impulse
  • Reaction time to a failure or rope movement is 1
    sec
  • In 1 sec a load will travel 16 feet

11
MECHANICAL ADVANTAGE
  • Simple Machines

12
MECHANICAL ADVANTAGE
  • Machines are affected by factors such as friction
    and elasticity
  • So the actual mechanical advantage of a simple
    machine will usually differ from its theoretical
    value.

13
MECHANICAL ADVANTAGE
  • Pulley
  • Pulleys change the direction of a tension force
    on a flexible material, e.g. a rope or cable. In
    addition, pulleys can be "added together" to
    create mechanical advantage, by having the
    flexible material looped over several pulleys in
    turn. More loops and pulleys increases the
    mechanical advantage.

14
MECHANICAL ADVANTAGE
  • Pulley as a Lever
  • The pulley is a variation of the wheel and axle.
  • The size of a pulley does not influence the MA.
  • The size of a pulley does influence the
    efficiency of the pulley.
  • The larger the pulley, the more efficient the
    pulley.

15
MECHANICAL ADVANTAGE
  • Pulley Types
  • Fixed pulley
  • Provides change of direction ONLY

16
MECHANICAL ADVANTAGE
  • Pulley Types
  • Movable pulley
  • Adds Mechanical Advantage

17
MECHANICAL ADVANTAGE
  • Pulley
  • Pulleys change the direction of a tension force
    on a flexible material, e.g. a rope or cable.
  • Pulleys can be "added together" to create
    mechanical advantage, by having the flexible
    material looped over several pulleys in turn.
  • More loops and pulleys can increase the
    mechanical advantage.

18
MECHANICAL ADVANTAGE
  • Pulley Efficiency
  • Two factors determine a pulley's efficiency
  • Sheave size the larger the sheave diameter, the
    higher the efficiency.
  • Bushings and bearings self-lubricating bushings
    are efficient, but they must be regularly
    maintained.Ball bearings are very efficient and
    since they are sealed, they do not require any
    maintenance.

19
MECHANICAL ADVANTAGE
  • Effective pulley systems must always have one
    side anchored and the other side attached to the
    moving load, known as the anchor side and the
    load side. There must be something to pull
    against.

20
MECHANICAL ADVANTAGE
  • The longest distance a pulley system can be
    stretched, the distance from the anchored pulley
    to the moving pulley, is called the stroke.
  • The longer the stroke, the more useful the MA
    system.

21
MECHANICAL ADVANTAGE
  • Pulling the system down to its smallest stroke is
    called compression.
  • It is called de-set when the system is compressed
    so it will expand again when using the MA system
    as the Decent Control Device (DCD) to lower a
    load rather than to raise it.

22
MECHANICAL ADVANTAGE
  • Extension means to pull out a pulley system to
    its longest stroke.
  • Set is called when the progress capture device
    is engaged, allowing extension to occur.
  • Re-set is called only when full extension has
    been completed during raising operations, and
    another haul segment is ready to be made on the
    main line.

23
MECHANICAL ADVANTAGE
  • All anchored pulleys are Change Of Direction
    (COD) only.

24
MECHANICAL ADVANTAGE
  • Pulleys that move with a load (unanchored
    pulleys) are simple machines that gain advantage.

25
MECHANICAL ADVANTAGE
  • Pulley systems are either simple, compound or
    complex.
  • Compound pulley systems are made up of at least
    two simple pulley systems.
  • Complex pulley systems are made up of at least
    one simple pulley system and at least one
    compound pulley system.

26
MECHANICAL ADVANTAGE
  • If the terminal end of a haul line is attached to
    the anchor, the simple pulley system will be EVEN
  • 21, 41, 61, 2481

27
MECHANICAL ADVANTAGE
  • If the terminal end of a haul line is attached to
    the LOAD, the simple pulley system will be ODD
  • 11, 31, 51, 1151

28
MECHANICAL ADVANTAGE
  • Simple pulley systems have a greater stroke than
    compound pulley systems of the same MA.

29
MECHANICAL ADVANTAGE
  • The Mechanical Advantage of a pulley system can
    be expressed as a ratio.
  • It is the ratio of the amount of force that must
    be applied to a haul line to move a load, divided
    by the weight of the object that must be moved.
  • It is the ratio of the weight of the object that
    must be moved to the amount of force that must be
    applied to move it.
  • 21 2 Units of output force will result from 1
    Unit of input force.
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