MACHINES and EFFICIENCY Chapter 9.8-9.9

Key Terms Mechanical Advantage (MA) Ideal Mechanical Advantage (IMA) A unitless ratio that indicates the number of times a machine multiplies your input force Ideal Mechanical Advantage (IMA) The calculated MA, does not consider friction Actual Mechanical Advantage (AMA) The measured or real MA, does consider friction Because of friction, AMA < IMA

Key Terms Work = Force x distance Simple machine Compound machine a device used to multiply forces or change the direction of forces Compound machine A machine composed of two or more simple machines

Key Terms Efficiency of a machine decreases as friction increases Friction increases the thermal energy by increasing molecular KE (non-mechanical energy) In other words… friction causes the particles to speed up, raising the average KE of the particles (and temperature!) Friction causes the useful work output to be less than the total work input

Key Terms Input (effort) Output (resistance) Input distance: the distance you input the force when using a machine Input force: the force you use when using a machine Output (resistance) Output distance: the distance the object that work is done on moves Output force: the force required to move the object without a machine (usually the weight of the object in newtons)

A simple machine Multiplies and redirects force Does not reduce the amount of work to be done, but makes work easier. MA > 1 means that your input force will be less than your output force (easier to do the work!) More leverage means more mechanical advantage If you increase MA, then Input force will decrease Input distance will increase

Key Terms Efficiency (a ratio) Measures the “wastefulness” of the transfer of energy More friction causes less efficiency Efficiency is calculated using the following equations: Actual mechanical advantage/idealized mechanical advantage Useful work output/total work input

Key Terms When using a machine… Work is done to move the object Work is done against friction Useful work output is the work done to move the object Total work input is work done to move object + work done against friction

Simple Machines Lever Inclined plane Two families --Lever --Pulley --Wheel and axle --Ramp --Wedge --Screw

LEVER FAMILY

The Lever fulcrum

Three Classes of Levers First class Examples: Crowbar See-saw

Three Classes of Lever Second class Examples: Wheelbarrow Door

Three Classes of Lever Third class Examples: Human arm Baseball bat

Calculating the Mechanical Advantage of a Lever MA = input distance/output distance which is… MA = length of effort arm/length of resistance arm. Effort or input distance Resistance or output distance 0.5 m 2.5 m Resistance arm Effort arm

Calculating the Mechanical Advantage of a Lever 2nd class lever 3rd class lever 2nd class levers decrease the input force but increase the input distance. 3rd class levers reduce the output force, but increase output distance and speed

Which lever would have the highest mechanical advantage and why? b has the largest input distance, giving the largest MA c b a

Pulley Fixed pulley 1 support rope IMA = 1

Pulleys IMA = 2 Two supporting ropes

Pulleys IMA = ? 2

Pulley How many support ropes? 4 What is the IMA? 4

Wheel and Axle Wheel connected to a shaft GIVES YOU LEVERAGE

INCLINED PLANE FAMILY

Inclined planes Ramps

Wedge Two inclined planes stuck together

Screw An inclined plane wrapped around a cylinder

What type of machine is this? Compound: made of two or more machines Two 1st class levers