MACHINES and EFFICIENCY Chapter 9.8-9.9

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 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)

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

A simple machine Multiplies and redirects force Does not reduce the amount of work to be done. Makes work easier. MA > 1 means that your input force will be less than your output force If you increase MA, then Input force will decrease Input distance will increase

Leverage and Mechanical Advantage Increasing leverage refers to an increase in mechanical advantage

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

LEVER FAMILY

The Lever fulcrum

Lever Output distance input distance 0.5 m 2.5 m Resistance arm Effort arm

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

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

Key Terms Efficiency (a ratio) 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!)

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

Calculating the Mechanical Advantage of a Lever MA = Resistance force ÷ effort force MA = length of effort arm ÷ length of resistance arm. 2.5 m 0.5 m Effort distance Resistance distance Resistance arm Effort arm

Which lever would have the highest mechanical advantage? b a

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