MachinesMachine:

  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/EnergyMachines obey the law of Conservation of Energy

 

Energy or Energy or Friction

Work into a + work out of + losses

Machine a machine

EfficiencyEfficiency:

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

Mechanical Advantage

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 = FR Resistance force

DE Applied force

 

MA = FE Applied Speed

DR Resistance Distance

Mechanical Advantage

If we apply 20N of force to move a 60N object

Solve problem on board

No unit on the number for MA

Forces on MachinesTwo forces involved with machines

  Effort Force: (FE)

  Force you put on a machine

  Resistance Force: (FR)

  Force the machine is working against (often the weight of the object)

Distances/MachinesEffort Distance: (DE)

  Distance of the effort force

 

Resistance Distance: (DR)

  Distance the object moves See word document (solve problems)

Lever LawLever law:

  Work in = work out 

F1D1 = F2D2

 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 PlaneEvery 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 PlaneInclined 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’sDemo with inclined plane, spring scale and weight

FR weight of object (lift with spring

scale)

FE spring scale drag

DE length of ramp

DR height of ramp

Slide object and do Force MA’s (MA = FR/FE)

Inclined Plane MA’sHow 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 LabSolve 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

WedgeWedge:

  An inclined plane that moves 

Examples: knife, axe, door stoop, wood splitting wedge…..

 How does sharpening a knife help it do more work?

ScrewScrew:

  An inclined plane wrapped around a cylinder  Examples: spiral staircase, mountain road,

C-clamp, bolts…  Each time a screw turns, it moves a

definite distance up or down.  

Depends on the distance between threads

Draw on chalkboard

LeverLever:

  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 MATheoretically, if you have a long and rigid enough lever you could lift anything (Webber)

 

MA = DE = Effort arm length

DR Resistance arm length Use word document for all 3 classes of levers and examples

Lever DemosWatch 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 AxleWheel 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 MACalculate MA of wheel and axle

 

MA = DE = Radius of wheel

DR 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

PulleysPulley

  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 ProblemsExample 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?

  F1D1 = F2D2

  A 46 N force is used to lift a 192 N weight. What is the MA?

Example ProblemsA 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?

Example ProblemsA 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.