Science 8: Unit E: Mechanical Systems

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Science 8 Unit E Mechanical Systems

• Topic 7 Machines Throughout History

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Why Did Humans Build Machines?

• The earliest machines were simple devices to make
  work easier like moving a boulder up an
  incline, splitting wood, or moving water against
  gravity.
• These machines used human or animal power as
  their energy source.
• Important examples include the mill (wheel and
  axle), plow (wedge), and catapult (lever)

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Machines and the Industrial Revolution

• The invention of the steam engine was a major
  turning point in civilization.
• The steam engine allowed people, materials, and
  goods to be moved much faster. This helped
  improve the standard of living, and greatly
  increased the number of jobs.
• A downside of the steam engine and the industrial
  revolution was that jobs that used to be
  performed by humans were now done by machines.

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The Steam Engine

• Invented in 1700s England by James Watt
• Used coal as an energy source. The coal would be
  burned, which heated a water supply, producing
  steam.
• The force of the steam would move a piston or
  turbine, which in turn would be attached to a
  crankshaft which would turn a wheel and axle
  system.
• The steam engine is known as an external
  combustion engine because the burning of the coal
  happened in an open container separate from the
  moving parts.
• The Steam Engine powered everything from factory
  machines to freighters to trains.
• Traditional steam engines have an efficiency of
  8

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The Internal Combustion Engine (ICE)

• Invented in 1876 Germany by Nikolaus Otto, but
  only became mainstream when Karl Benz modified it
  and put it in his cars.
• The combustion occurs inside the engine itself,
  making it more efficient and safer.
• The crankshaft changes the linear motion of the
  piston to the rotational motion of the wheel and
  axle system.
• The average efficiency of an ICE 20.

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ICE Contd

• The moving pistons go through 4 steps
• 1. Intake Stroke Fuel enters engine.
• 2. Compression Stroke Piston compresses
  fuel-air mixture.
• 3. Power Stroke Mixture is ignited by a spark
  plug, moving the piston.
• 4. Exhaust Stroke Waste products are released.

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The Importance of the ICE

• Allowed transportation to become individualized
  as ICEs led to smaller autos and even
  motorcycles.
• Steam engines were too large and heavy for
  aircraft so ICEs led to the first planes.

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Beyond the ICE

• Engineers and scientists are working to improve
  or replace the ICE.
• The electric motor is more efficient than the
  ICE.
• Maglev trains move on a magnetic rail without
  touching the rails themselves. This reduces
  friction and makes the system very efficient.
• The Maglev train technology was accidentally
  discovered by physicists doing unrelated science.