9 Mechanical Power Systems

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).

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

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.

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

Simple Machines Levers Pulleys Wheels and axles Inclined planes Screws Wedges

Simple Machines

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

What type of quantity is displacement? Vector quantities

Actual mechanical advantage (AMA) The ratio of the increase of force or distance by a machine, including energy lost through friction. Bearing A specially shaped piece of metal used to support shafts and reduce friction between metal parts as they move past or revolve around each other. Brake horsepower (bhp) The amount of power available at the rear of the engine under normal conditions. Clutche A mechanical device that connects the power source to the rest of the machine.

Frictional horsepower (fhp) Displacement A vector quantity that includes both distance and direction. First-class lever A lever that has the fulcrum positioned between the input force and the load. Frictional horsepower (fhp) The amount of hp necessary to overcome the internal friction of an engine and other forms of frictional loss. Fulcrum The fixed point around which a lever rotates.

Ideal mechanical advantage (IMA) A ratio of the forces or the distances involved in a mechanism. It assumes 100% efficiency. Inclined plane A simple machine that makes use of sloping surfaces. Indicated horsepower (ihp) The maximum potentional hp produced by an engine under ideal conditions. Lever A rigid bar that rotates around one fixed point.

Prony brake Pulley Scalar quantity A device used to measure the effort produced by a twisting or turning force. It is based on the principle that if an opposite force equals the effort produced by a spinning object, movement will cease. Pulley A solid disc that rotates around a center axis. It usually has a groove around the outside edge that allows ropes or belts to easily ride around them. Scalar quantity A physical quantity specified by the magnitude of the quantity and expressed by a number or unit.

Screw Second-class lever Shaft Simple machine A simple machine consisting of a very long inclined plane wrapped around a shaft. Second-class lever A lever that has the load placed between the fulcrum and the input force. Shaft A long, cylindrical piece of metal used to transfer mechanical energy in many types of machines. Simple machine A lever, a pulley, a wheel and axle, an inclined plan, a screw, or a wedge.

Third-class lever Universal joint Vector quantity Velocity A lever that has the input force positioned between the fulcrum and the load. Universal joint A joint that allows connected shafts to spin freely, while permitting a change in direction. Vector quantity A quantity that has both magnitude and direction. Velocity A vector quantity that includes speed and direction.

Wedges A simple machine based on the principle of the inclined plane. Wheel and axle A large-diameter wheel and its small-diameter axle are attached to each other to move as one unit.