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 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.