MACHINES and EFFICIENCY Chapter

Key Terms Work = Force x distance Simple 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) ◦ 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) ◦ 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, but makes work easier. MA > 1 means that your input force will be less than your output force More leverage means more mechanical advantage If you increase MA, then ◦ Input force will decrease ◦ Input distance will increase

Key Terms Efficiency (a ratio) ◦ Is calculated using the following equations: ◦ Actual mechanical advantage/idealized mechanical advantage ◦ Useful work output/total work input

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 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 Two families LeverInclined plane --Lever --Pulley --Wheel and axle --Ramp --Wedge --Screw

fulcrum The Lever

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 armResistance arm 2.5 m 0.5 m Effort or input distance Resistance or output distance

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

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

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 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 1 st class levers