Science 8: Unit E: Science 8: Unit E: Mechanical SystemsMechanical Systems

Topic 7: Machines Throughout Topic 7: Machines Throughout HistoryHistory

Why Did Humans Build Machines?Why Did Humans Build Machines?

The earliest machines The earliest machines were simple devices to were simple devices to make work easier; like make work easier; like moving a boulder up an moving a boulder up an incline, splitting wood, or incline, splitting wood, or moving water against moving water against gravity.gravity.

These machines used These machines used human or animal power human or animal power as their energy source.as their energy source.

Important examples Important examples include the mill (wheel include the mill (wheel and axle), plow (wedge), and axle), plow (wedge), and catapult (lever)and catapult (lever)

Machines and the Industrial Machines and the Industrial RevolutionRevolution

The invention of the steam engine was a The invention of the steam engine was a major turning point in civilization.major turning point in civilization.

The steam engine allowed people, materials, The steam engine allowed people, materials, and goods to be moved much faster. This and goods to be moved much faster. This helped improve the standard of living, and helped improve the standard of living, and greatly increased the number of jobs.greatly increased the number of jobs.

A downside of the steam engine and the A downside of the steam engine and the industrial revolution was that jobs that used to industrial revolution was that jobs that used to be performed by humans were now done by be performed by humans were now done by machines.machines.

The Steam EngineThe Steam Engine Invented in 1700s England by James WattInvented in 1700s England by James Watt Used coal as an energy source. The coal would be Used coal as an energy source. The coal would be

burned, which heated a water supply, producing burned, which heated a water supply, producing steam.steam.

The force of the steam would move a piston or The force of the steam would move a piston or turbine, which in turn would be attached to a turbine, which in turn would be attached to a crankshaft which would turn a wheel and axle crankshaft which would turn a wheel and axle system.system.

The steam engine is known as an external The steam engine is known as an external combustion engine because the burning of the coal combustion engine because the burning of the coal happened in an open container separate from the happened in an open container separate from the moving parts.moving parts.

The Steam Engine powered everything from factory The Steam Engine powered everything from factory machines to freighters to trains.machines to freighters to trains.

Traditional steam engines have an efficiency of ~8%Traditional steam engines have an efficiency of ~8%

The Internal Combustion Engine The Internal Combustion Engine (ICE)(ICE)

Invented in 1876 Germany by Nikolaus Invented in 1876 Germany by Nikolaus Otto, but only became mainstream when Otto, but only became mainstream when Karl Benz modified it and put it in his cars.Karl Benz modified it and put it in his cars.

The combustion occurs inside the engine The combustion occurs inside the engine itself, making it more efficient and safer.itself, making it more efficient and safer.

The crankshaft changes the linear motion The crankshaft changes the linear motion of the piston to the rotational motion of the of the piston to the rotational motion of the wheel and axle system.wheel and axle system.

The average efficiency of an ICE ~ 20%.The average efficiency of an ICE ~ 20%.

ICE Cont’dICE Cont’d

The moving pistons go through 4 steps:The moving pistons go through 4 steps: 1. Intake Stroke – Fuel enters engine.1. Intake Stroke – Fuel enters engine. 2. Compression Stroke – Piston 2. Compression Stroke – Piston

compresses fuel-air mixture.compresses fuel-air mixture. 3. Power Stroke – Mixture is ignited by a 3. Power Stroke – Mixture is ignited by a

spark plug, moving the piston.spark plug, moving the piston. 4. Exhaust Stroke – Waste products are 4. Exhaust Stroke – Waste products are

released.released.

The Importance of the ICEThe Importance of the ICE

Allowed transportation to become Allowed transportation to become individualized as ICEs led to smaller autos individualized as ICEs led to smaller autos and even motorcycles. and even motorcycles.

Steam engines were too large and heavy Steam engines were too large and heavy for aircraft so ICEs led to the first planes.for aircraft so ICEs led to the first planes.

Beyond the ICEBeyond the ICE Engineers and scientists are working to improve Engineers and scientists are working to improve

or replace the ICE.or replace the ICE. The electric motor is more efficient than the ICE.The electric motor is more efficient than the ICE. Maglev trains move on a magnetic rail without Maglev trains move on a magnetic rail without

touching the rails themselves. This reduces touching the rails themselves. This reduces friction and makes the system very efficient.friction and makes the system very efficient.

The Maglev train technology was accidentally The Maglev train technology was accidentally discovered by physicists doing unrelated discovered by physicists doing unrelated science.science.