Machines Machine: A device that helps you do work All machines are made up of one or more simple machines Machines make work easier by changing the size or direction of force

Machines/Energy Machines obey the law of Conservation of Energy Energy orEnergy orFriction Work into a +work out of +losses Machinea machine

Efficiency Efficiency: Comparison of work output to work input All machines have friction losses 100% efficient machine (no friction or heat losses) does not exist

Mechanical Advantage Mechanical Advantage (MA): How many times easier a machine makes your work Number of times a machine multiplies effort force No Unit for MA

You want a robot with a MA of 10 instead of 5, as work will be 10 times harder rather than 5 times easier MA = F R Resistance force D E Applied force MA = F E Applied Speed D R Resistance Distance

If we apply 20N of force to move a 60N object Solve problem on board No unit on the number for MA

Forces on Machines Two forces involved with machines Effort Force: (F E ) Force you put on a machine Resistance Force: (F R ) Force the machine is working against (often the weight of the object)

Distances/Machines Effort Distance: (D E ) Distance of the effort force Resistance Distance: (D R ) Distance the object moves See word document (solve problems)

Lever Law Lever law: Work in = work out F 1 D 1 = F 2 D 2 An 800N man is 2 meters from the fulcrum of a teeter-totter. How far away must a 400N child sit in order to balance?

Mechanical Advantage A person pushes a crowbar down 2 m with 200N of force. The crowbar raises the box 0.3 m. What is the MA? Show work/PE/KE/Power Eureka videos

Six simple machines 6 simple machines: Inclined Plane Wedge Screw Lever Wheel and axle Pulley

Inclined Plane Every day my lovely wife lifts 3000 pounds 5 feet. She does this 2, 4 or 6 times a day, depending on the day. What is she doing? Driving her car up the driveway

Inclined Plane: A slanted surface used to move an object from low to high or high to low position. Examples: driveway, ramp, stairs, road Show Eureka Inclined plane video

Inclined Plane MA’s Demo with inclined plane, spring scale and weight F R weight of object (lift with spring scale) F E spring scale drag D E length of ramp D R height of ramp Slide object and do Force MA’s (MA = F R /F E )

How will MA vary with height? Steeper inclined plane = less MA Less steep inclined plane = large MA (easier) Example: Climb a mountain - steep sections harder to climb

Inclined Plane Lab Solve Inclined Plane problems in word document Demo lab. Groups of 3 – 4 do lab and turn it in. Review lab

Inclined Plane Review Quick review of inclined plane: See word document for quality graphic and formulas How will MA vary with height for an inclined plane? Steeper inclined plane: less MA, more difficult to use Less steep inclined plane: larger MA, easier to use

Wedge Wedge: An inclined plane that moves Examples: knife, axe, door stoop, wood splitting wedge….. How does sharpening a knife help it do more work?

Screw Screw: An inclined plane wrapped around a cylinder Examples: spiral staircase, mountain road, C-clamp, bolts… Each time a screw turns, it moves a definitedistance up or down. Depends on the distance between threads Draw on chalkboard

Lever Lever: A bar that rotates on a fixed point called a fulcrum Fulcrum The fixed point a lever rotates around MA’s can be very large, depends on leverage

Lever MA Theoretically, if you have a long and rigid enough lever you could lift anything (Webber) MA = D E = Effort arm length D R Resistance arm length Use word document for all 3 classes of levers and examples

Lever Demos Watch Eureka video on levers Demo lever activity Students calculate MA and list class of lever Demo lever law with meter stick and weights Wheel and axle demos

Wheel and Axle Wheel and Axle A lever that moves in a circle turning another circle Examples: screw driver, socket wrench, faucet knob, steering wheel, pencil sharpener, door knob…

Wheel and Axle MA Calculate MA of wheel and axle MA = D E = Radius of wheel D R Radius of axle See word documents

Advantages of a Machine What are the two advantages of a machine? They change the size and direction of effort force

Pulleys Pulley A lever that rotates around a fixed point 2 benefits of a pulley 1. Change the direction of force 2. Provide Mechanical Advantage Bag the technology and go back to the chalk board like our ancestors

Example Problems Example problems: George weighs 700 N and is 5 meters from the fulcrum on a teeter-totter. How far must Martha be from the fulcrum to balance if she weighs 200 N? F 1 D 1 = F 2 D 2 A 46 N force is used to lift a 192 N weight. What is the MA?

A lever is used to lift a 2000 N weight with an effort force of 50 N. What is the MA of the bar? What is the MA of a ramp 30 meters long and 4 meters high?

A woman pushes a crow bar down 3 meters to pry a spike out 0.15 meters. What was the MA? Create and solve 8 MA problems (4 with distance and 4 with force) and 2 lever law problems (teeter-totter). Turn this in for easy points.