Mechanical Power Systems

2. 9 Mechanical Power Systems

3. Basic Concepts • List the six simple machines and give an example of each. • List three types of gears. • Name the two primary characteristics of power. • Identify two mechanical transmission devices and describe how each operates. • Define mechanical advantage and give an example. • Recognize the difference between the ideal mechanical advantage (IMA) and actual mechanical advantage (AMA).

4. Intermediate Concepts • Discuss force and rate in a mechanical system. • Describe the difference between scalar and vector quantities.

5. Advanced Concepts • Design a mechanical system for a specific application. • Predict the result of a mechanical system based on knowledge of balanced and unbalanced loads. • Calculate the mechanical advantage of a simple machine. • Compute the mechanical advantage of compound machines. • Solve for the percentage of frictional loss in a mechanical system.

6. Mechanical Systems • Produce work using one or more machines • Machines can change size, direction, and speed of forces • Machines can change type of motion produced

7. Simple Machines • Levers • Pulleys • Wheels and axles • Inclined planes • Screws • Wedges

8. Simple Machines

9. Levers • Rotates around fulcrum • Position of fulcrum, load, and input force determines lever class • First-class levers • Second-class levers • Third-class levers

10. Pulleys • Discs rotating around center axis • Operate on principle of levers • Several pulleys together make block and tackle

11. Wheels and Axles • Also based on principle of levers • Large-diameter wheel and small-diameter axle are attached to each other • Can be used to change size or distance of force

12. Inclined Planes • Makes use of sloping surfaces • Rolling objects up slopes is easier than lifting objects • Much less force to achieve same result

13. Screws • Operates on principle of inclined planes • Long incline plane wrapped around shaft • Screws with more threads per inch have advantages • Apply greater force • Create for surface area to produce friction

14. Wedges • Consist of two inclined planes placed back to back • Often used to split materials • Hatchets are wedges that use weight and fast movement to split wood

15. Gears • Metal wheel with small notches cut into rim • Gear sets are made so gear teeth interlock and drive each other • Gears can control mechanical power in the same way as belts and pulleys • Gears change direction of power, speed, and torque

16. Quantities of Measurement • Scalar quantity represents physical quantity and is expressed by number or unit • Vector quantities have both magnitude and direction • Displacement • Velocity

17. Torque • Force that produces twisting or turning effect or rotation • Two components • Amount of force applied to lever arm • Radius of lever arm itself • Measured using Prony brake

18. Horsepower (hp) • Rate at which output work is performed • Several types of hp ratings: • Indicated horsepower (ihp) • Brake horsepower (bhp) • Frictional horsepower (fhp)

19. Net Forces of Balanced and Unbalanced Loads • Balanced forces are in state of equilibrium • Movement ceases in balance • Forces of effort and opposition must be totally balanced • Unbalanced loads can be calculated with addition and subtraction

20. Transmission of Mechanical Energy • Compound machines use two or more simple machines • Variations in simple machines may be used • Operations of industrial machines and transportation vehicles rely on principles of one or more simple machines

21. Clutches • Connects power source to rest of machine • Device is needed so vehicles can remain at rest with engine running, start without stalling, and shift gears while moving • Operate on principle of friction • Types in vehicles are diaphragm clutch and centrifugal clutch

22. Pulleys and Belts • Many belts move around pulleys in vehicles • Transmit power from engine to drive engine components, such as water pump and fan • Control mechanical energy through five different arrangements

23. Chains and Sprockets • Found on bicycles, mopeds, and motorcycles • Usually used as drive system to bring power to driving wheel of vehicle • Provide positive power transfer, which means chain cannot slip like belt on pulley

24. Shafts and Bearings • Shafts are vital parts of automobile engines and drive systems • Bearings are made to be strong and allow shaft to turn inside them • Shafts are not easily bent, so universal joints are used when flexibility is needed

25. Mechanical Advantage • Simple machines can gain mechanical advantage • Levers • Pulleys • Wheels and axles • Inclined planes • Wedges • Gears

26. Ideal Mechanical Advantage vs. Actual Mechanical Advantage • Ideal mechanical advantage (IMA) • Actual mechanical advantage (AMA) • Accounts for loss of energy through friction • Friction is heat energy that is common by-product of mechanical energy • AMA is always less than IMA because IMA assumes for 100% efficiency • AMA accounts for frictional losses

27. What are the six simple machines? Levers, pulleys, wheels and axles, inclined planes, screws, and wedges

28. What two simple machines also operate on the principle of the lever? Pulleys and wheels and axles

29. What type of quantity is displacement? Vector quantities