Unit D: Mechanical Systems I - Kurpinski's Class

Introduction to Machines

• Machines are tools that enhance human ability to perform work by utilizing energy effectively.

Definition of Machine

• A device that assists in doing work.
• Example: A combine harvester represents technological advancement.

Simple Machines Meeting Human Needs

Early Machines

• Simple devices relying on human and animal energy.
• Examples include the plow, windmill, and watermill.

Water Transportation in Early Civilizations

• Roman Aqueducts: Transported water over long distances to cities using pumps, channels, and a distribution system.
• Sakia (Persian Wheel): Used animal power to raise water stored in tanks, then moved by gravity.
• Archimedes Screw: Used to lift water, initially powered by hand, later by motors. Modern pumps may still use this method.

Simple Machines

Definition of Simple Machine

• A tool made of one basic machine, designed to make work easier by altering the force applied.
• Six types: Lever, Inclined Plane, Wedge, Screw, Pulley, Wheel and Axle.

Types of Simple Machines

1. Lever
   • Rigid bar rotating around a fulcrum.
   • Three types: First, Second, and Third class levers.
2. Inclined Plane
   • Flat, sloped surface making it easier to move loads.
3. Wedge
   • Like an inclined plane, used to split objects by applying force.
4. Screw
   • Cylinder with a spiral groove, converts rotational to linear motion.
5. Pulley
   • Rope or cable on a wheel, used to lift loads.
   • Block and tackle systems increase lifting strength.
6. Wheel and Axle
   • Two wheels of different diameters, increase force or speed by changing torque and rotational speed.

Complex Machines

Definition and Need

• Combinations of simple machines forming complex systems as societies advanced.
• Dependence on new energy sources led to the industrial revolution.
• Improved living standards but increased reliance on technology.

Components

• System: Multiple parts working together.
• Subsystem: Smaller parts within a complex machine, each with specific functions (e.g., a bike's subsystems).

Subsystems in Force Transfer

• Linkage: Transfers energy in devices like bicycle chains.
• Transmission: Transfers energy in vehicles.

Gears

• Interlocking wheels with teeth change the speed, force, and direction of motion.
• Important concepts: Driving and Driven gears, gear trains, sprockets.

Mechanical Advantage and Efficiency

Mechanical Advantage (MA)

• The extent a machine multiplies force.
• Calculated: MA = Output Force / Input Force.

Speed Ratio (Gear Ratio)

• Measures how a machine affects speed, often inversely related to force.
• Calculated as Speed Ratio = Input Distance / Output Distance.

Efficiency

• How well a machine uses energy, affected by friction.
• Efficiency = (MA / Speed Ratio) x 100.
• Includes calculating work: Work (J) = Force (N) x Distance (m).

The Effect of Friction

• Opposes motion, causing inefficiency by converting energy to heat.

Work and Power

Work

• Calculated when force moves an object over a distance.
• Work = Force x Distance, measured in Joules (J).

Power

• Work done over time, measured in Watts.
• Power = Work / Time.

Energy and Work

• Interrelated; machines don’t reduce work but the force needed.
• Efficiency can also be calculated as Efficiency = (Work Output/Work Input) x 100.

Assignments and Exercises

• Practical calculations involving simple machines, gear ratios, mechanical advantage, and efficiency.