Unit 3 “Simple Machines”

Definition of a Simple Machine A device that makes work easier –Changes the size or direction of a force –Has only one motion

Types of Simple Machines Simple machines are grouped into six types  plane  screw  lever  wedge  wheel and axle  pulley

Compound Machines A compound machine is a combination of simple machines that work together.

Advantage of Using a Simple Machine Can change the direction of the force –Applying the force may be easier

Can magnify the force –Allows a smaller force to be used, –but the distance must increase! The amount of Work is still the same! Advantage of Using a Simple Machine You never get something for nothing!

Mechanical Advantage “Work In = Work Out” Since W = F  d Therefore F i  d i = F o  d o Effort force Distance effort has moved Force that must be overcome Distance resistance has moved

What the number means –Compares the input or effort force to the output force or resistance force –Tells the number of times a machine increases the force Mechanical Advantage F i F o

Inclined Plane Sloped surface used to make lifting easier MA = height length lhlh length of ramp height of ramp

The Screw A screw is an inclined plane wrapped around a rod Used to hold objects together MA = 2  r r l g gap   twice the radius of rod length of gap radius of rod Note: 2  r =  d Don’t measure the top!

Wedge A wedge is an inclined plane with two sloping surfaces Used to cut MA = height width hwhw height of wedge width of wedge

Levers A lever is a bar that is free to move about a pivot point A lever has three parts –effort arm –fulcrum –resistance arm fulcrum resistance arm effort arm

Types of Levers Levers are grouped into three classes Third Class Second Class First Class

First Class Lever Fulcrum in the middle of the bar Examples –Balance –Paint can –Teeter-totter effort force resistance force

Second Class Lever Resistance force (load) is in the middle Examples –wheel barrow –door –nut cracker resistance force effort force

Third Class Lever Effort force is in the middle Examples –baseball bat –fishing pole –canoe paddle –broom resistance force effort force

Mechanical Advantage of Levers MA = effort arm resistance arm didodido length of effort arm length of resistance arm

Wheel and Axle Two wheels of different sizes Connected and move together Examples –door knob –pencil sharpener –screw driver smaller wheel larger wheel

Wheel and Axle A wheel and axle act like a circular lever. small force in Large force out By turning the large blue wheel, The smaller yellow axle also turns.

Wheel and Axle Or, the two can be used in reverse. Small distance in Large distance out By turning the small yellow axle The larger blue wheel also moves.

MA of Wheel and Axle MA = dwdadwda diameter of wheel diameter of axle  wheel axle

Pulleys A pulley is a surface with a chain or rope going around Used to lift heavy objects Two types –Fixed –movable

Types of Pulleys Fixed Pulley –Pulley is fastened into position –Changes the direction of force –Does not magnify the force fixed pulley

Types of Pulleys movable pulley Movable Pulley –Pulley is fastened to the load –Load is shared between both ends of the line –Only half the force is needed to lift the load

MA of a Pulley MA = number of lines supporting the load –Don’t count the line that is being pulled. MA = 1 One line is supporting the load. MA = 2 Two lines are supporting the load.

Efficiency Efficiency is the ability to convert input work into actual work output. –no machine is perfect –loss caused by friction

Calculating Efficiency WOWIWOWI Efficiency =  100 Input Work Output Work Ideal machines have 100% efficiency.