Transcript Science 8: Unit E: Mechanical Systems

Science 8: Unit E:
Mechanical Systems
Topic 7: Machines Throughout
History
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)
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.
The Steam Engine
 Invented in 1700s England by James Watt
 Used coal as an energy source. The coal would be
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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%
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%.
ICE Cont’d
 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.
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.
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.