Name _______________________________________ Date ______________  Period ________

 

Notes on Simple Machines

I.                   Simple Machines

A.     The purpose of a simple machine is to make work easier.

B.      Mechanical Advantage (MA): can be calculated to figure out how much a machine multiplies your force

1. MA = Resistance/Effort

a.       Effort: force applied to the machine (by you!)

b.      Resistance: force applied by the machine OR the object that is being moved

II.               Six types of simple machines

A.     lever

B.      pulley

C.      wheel and axle

D.     inclined plane

E.      screw

F.      wedge

III.           Lever: a simple machine made with a bar free to move about a fixed point

A.     Parts of a lever:

1.       Effort: force applied to the machine (by you!)

2.      Resistance: force applied by machine (or the object being moved)

3.      Fulcrum: fixed point

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                                                                                                 Effort                Resistance

   

                                                                                                            Fulcrum

B.      Three classifications of levers:

1.       1st class lever: fulcrum is between the effort and resistance such as a seesaw (above)

a. The MA depends on the position of the fulcrum!

MA < 1

MA = 1

MA > 1

b.   The purpose of a 1st class lever is typically to change direction.

c.       Examples: scissors, pliers, hammer pulling a nail, seesaw, crowbar, oar on a row boat, etc

2.      2nd class lever: resistance is between force and effor

            a.       The MA is greater than 1 (MA > 1)

b.      The purpose of a 2nd class lever is to increase force.

c.       Examples: bottle opener, wheel barrow, dolly, stapler, etc

Text Box:

         

3.      3rd class lever: effort is between fulcrum and resistance

a.       The MA is less than 1 ( MA < 1)

b.      The purpose of a 3rd class lever is typically to increase speed and/or distance.

c.       Examples: baseball bat, shovel, tweezers, hammer, your arm, etc                                                         

C.      To calculate MA of a lever:

         1. MA = Distance from fulcrum to input force/ Distance from the fulcrum to output

force

IV.              Pulley: wheels with a rope or chain wrapped around them

A.     Three types of pulleys:

1.       Fixed Pulley:

1st class lever

MA = 1 (The purpose of a fixed pulley is to change direction; therefore, you would not use it to increase your force to lift something heavy.)

The top of a shade has a fixed pulley

2.      Movable Pulley:

2nd class lever

MA = 2

A sail is a movable pulley

3.      Block & Tackle: combination of fixed and movable pulleys

MA ≥ 2

MA = the number of sections of the rope that support the object (This does not include the rope on which you pull downward, because it does not support the object.)

Used to lift and move heavy objects

V.                  Wheel and axle: two wheels of different sizes that rotate together

A.     1st class lever

B.      Your effort (Fe) is applied to the larger wheel which turns the smaller wheel (Fr).

C.      Examples: screw driver, door knob, faucet, meat grinder, pencil sharpener, steering wheel, etc

D.     To calculate MA of a wheel and axle:

         1. MA = Radius of wheel/ Radius of axle

VI.              Inclined Plane: a sloping surface used to raise objects

A.     An inclined plane allows you to exert less force over a greater distance.

B.      MA= Length of slope/ Height of slope

C.      Examples: ramp, ladder, and stairs

VII.          Screw: an inclined plane wrapped in a spiral around a cylindrical post

A.     The closer the threads, the greater the MA

B.      Example: jar lid

VIII.      Wedge: an inclined plane with one or two sloping sides

A.     Examples: chisels, knives, axe blades, push pin, tack, etc

IX.             Simple Machines can be divided into two groups:

A.     levers: a pulley and a wheel and axle are types of levers

B.      inclined planes: a screw and a wedge are types of inclined planes

X.                 Compound Machine: a machine that utilizes two or more simple machines.