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Mechanical Systems

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Title: Mechanical Systems


1
Mechanical Systems
  • Unit Review

2
Early Machines
  • machines help us do work and use energy more
    efficiently
  • early machines were simple devices to help us do
    work such as lift things, move things, crush
    things, or split things

3
Industrial Revolution
  • now we had power such as steam, coal, oil
  • and we could improve the ability of machines to
    do work for us

4
Simple Machines
  • levers
  • winches
  • incline planes
  • wedges
  • screws
  • pulleys
  • complex machines are several simple machines
    working together

5
Levers
  • simple machine that changes the amount of force
    needed to move an object
  • made up of a bar that is free to rotate around a
    fixed point called a fulcrum
  • force exerted on the lever to make it move is the
    effort force
  • the mass of the object being moved is called the
    load
  • distance between fulcrum and load is called the
    load arm

6
3 Classes of Levers
E
L
L
L
F
F
F
E
E
E Effort Force L Load F Fulcrum
7
Winches
  • consists of a small cylinder that has a crank or
    handle to produce effort force.
  • axle of the winch acts like the fulcrum
  • by exerting a force on the handle to turn the
    wheel the cable retracts the load

8
Incline Plane
  • a ramp or slope that reduces the force needed to
    lift something
  • it does this by increasing the distance over
    which the work is done

9
Screw
  • its an incline plane that is wound around a
    central post
  • helps to increase the force used
  • by rotating the screw, the incline plane pushes
    it forward (or into something), the screw
    slowly travels a straight distance
  • examples
  • screw
  • spiral staircase
  • jar lid

10
Wedge
  • similar in shape to an incline plane
  • works only in one direction
  • when pushed into an object it gradually splits it
    apart
  • e.g. axe head splitting wood or a knife cutting
    something

11
Pulleys
  • consists of wire, rope or chain moving on a
    grooved wheel
  • designed to help lift large loads
  • fixed pulley is attached to something that does
    not move (e.g. ceiling)
  • moveable pulley is attached to something else,
    but the pulley can move

12
  • block and tackle uses a combination of fixed and
    moveable pulleys to make a supercharged system
    that can move very heavy loads
  • when multiple pulleys are used in a system its
    called a compound pulley

13
Wheel and Axle
  • combination of two wheels of different diameters
    that turn together
  • one is called the wheel the other the axle
  • the longer the motion on the wheel the greater
    the force on the axle the more work gets done

14
Complex Machines
  • several simple machines working together
  • a system is a group of parts that work together
    to perform a function
  • subsystems are usually simple machines
  • linkages for the network or link between the
    subsystems so the system works

15
A Bicycle is a Complex Machine
16
Brakes in a Car are a Complex Machine
17
Gears
  • gears are an essential component of most
    mechanical systems BECAUSE they transfer energy
  • consist of a pair of wheels with teeth that
    interlink
  • can be used to increase or decrease speed of the
    mechanical system
  • can be used to change the direction of motion of
    the mechanical system

18
A smaller gear (Y) is called a pinion. The
gear that supplies the energy is called the
driving gear (X). The gear to which the force
is directed is called the driven gear (Y). A
large gear (X) driving a smaller gear (Y)
decreases torque and increases speed in the
driven gear. Gears such as these are called
multiplying gears. A small gear (Y) driving a
larger gear (X) increases torque and reduces
speed in the driven gear. Gears like these are
called reducing gears. When the driving gear
has fewer teeth than the driven gear, the driven
gear then rotates more slowly than the driving
gear. A car or bicycle in low gear uses reducing
gears. When the driving and the driven gears are
the same size they are known as parallel gears.
19
Work
  • work is energy in action
  • if there is no movement of object there is no
    work
  • Work Force x Distance
  • how much force was applied, and for how far
  • work is measured in Joules (J)
  • work input is the work you apply on the machine
  • work output is the work the machine does on the
    load

20
Mechanical Advantage
  • is a comparison of the force produced by a
    machine to the force applied to the machine (by
    you)
  • Mechanical Advantage (MA) Load force (FL) or
    Output Force
  • Effort force (FE) Input Force
  • or for levers, MA effort arm
  • load arm
  • load force and effort force are both measured in
    Newtons (N), therefore MA has no units of measure
  • MA can be lt1, 1 or gt1

21
Mechanical Advantage - Pulleys
  • to calculate the MA of a pulley, count the number
    of ropes/cables supporting the load

22
MA lt1
  • when MA is gt1 the machine is multiplying the
    input force to create a larger output force
  • when MA is lt1 it is useful for tasks that dont
    require a large output force
  • e.g. a bicycle is a machine with a MA lt1
  • the output force causes the bicycle to move
    faster than the rider could walk, so it is a very
    useful machine

23
Friction
  • the difference between the calculated value and
    the real (actual) value of mechanical advantage
    is friction
  • friction is essentially a force that opposes
    motion
  • it is caused by the roughness of materials
  • force is always needed to overcome friction
  • so the MA of the device will be less because of
    this added force that must be overcome
  • friction in a system causes heat

24
Speed Ratio
  • speed measures the distance an object travels in
    a given amount of time
  • the measure of how a machine affects speed is
    called the speed ratio (SR)
  • SR input distance OR d input (m)
  • output distance d output (m)

25
Efficiency
  • efficiency is a measure of how well a machine or
    a device uses energy
  • the more energy that is lost, the less efficient
    a machine is
  • friction is a main factor in loss of energy
  • efficiency is represent in .
  • Efficiency () Mechanical Advantage X 100
  • Speed Ratio
  • lubricants can be used to reduce friction and
    improve efficiency
  • NO MACHINE CAN BE 100 EFFICIENT !!!!

26
Hydraulic Systems
  • liquids are placed under pressure in a confined
    space
  • because they are relatively incompressible the
    can transmit that pressure to do work like
    lifting very heavy objects
  • pressure in liquids is measured in Pascals (Pa)
  • P F/A
  • F is force (N)
  • A is area (m2)

Pressure
Lift
27
Pneumatic Systems
  • air or gas is placed under pressure in a confined
    space
  • operates essentially like a hydraulic system
  • e.g. sand blaster, air gun, nail gun, jackhammer,
    hovercraft
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