Simple Machines

1
Simple Machines
2
Simple Machines

• Have few or no moving parts
• Make work easier
• Can be combined to create complex machines
• Six simple machines Lever, Inclined Plane, Wheel
  and Axle, Screw, Wedge, Pulley

3
Lever

• A rigid board or rod combined with a fulcrum and
  effort
• By varying position of load and fulcrum, load can
  be lifted or moved with less force
• Trade off must move lever large distance to move
  load small distance
• There are 3 types of levers

4
1st Class Lever

• The fulcrum is located between the effort and the
  load
• Direction of force always changes
• Examples are scissors, pliers, and crowbars

5
2nd Class Lever

• The resistance is located between the fulcrum and
  the effort
• Direction of force does not change
• Examples include bottle openers and wheelbarrows

6
3rd Class Lever

• The effort is located between the fulcrum and
  the resistance
• Direction of force does not change, but a gain in
  speed always happens
• Examples include ice tongs, tweezers and shovels

7
Mechanical Advantage

• We know that a machine multiplies whatever force
  you put into it
• - Using a screwdriver to turn a
  screw
• - Twisting a nail with pliers
• - Carrying a box up a ramp
  instead of stairs
• The amount that the machine multiplies that force
  is the mechanical advantage of the machine
• Abbreviated MA

8
Mechanical Advantage

• (IMA) Ideal MA This is the MA of a machine in a
  world with no friction, and no force is lost
  anywhere
• (AMA) Actual MA This is simply the MA of a
  machine in the world as we know it
• - Force is lost due to friction
• - Force is lost due to wind,
  etc.
• Can we have an ideal machine?

9
Mechanical Advantage Lever

• The mechanical advantage of a lever is the
  distance from the effort to the fulcrum divided
  by the distance from the fulcrum to the load
• For our example,
• MA 10/5 2

• Distance from effort to fulcrum 10 feet
• Distance from load to fulcrum 5 feet

10
Inclined Planes

• A slope or ramp that goes from a lower to higher
  level
• Makes work easier by taking less force to lift
  something a certain distance
• Trade off the distance the load must be moved
  would be greater than simply lifting it straight
  up

11
Mechanical Advantage Inclined Plane

• The mechanical advantage of an inclined plane is
  the length of the slope divided by the height of
  the plane, if effort is applied parallel to the
  slope
• So for our plane
• MA 15 feet/3 feet 5

• Lets say S 15 feet, H 3 feet

12
Wheel and Axle

• A larger circular wheel affixed to a smaller
  rigid rod at its center
• Used to translate force across horizontal
  distances (wheels on a wagon) or to make
  rotations easier (a doorknob)
• Trade off the wheel must be rotated through a
  greater distance than the axle

13
Mechanical Advantage Wheel and Axle

• The mechanical advantage of a wheel and axle
  system is the radius of the wheel divided by the
  radius of the axle
• So for our wheel and axle MA 10/2 5

14
Screw

• An inclined plane wrapped around a rod or
  cylinder
• Used to lift materials or bind things together

15
Mechanical Advantage Screw

• The Mechanical advantage of a screw is the
  circumference of the screwdriver divided by the
  pitch of the screw
• The pitch of the screw is the number of threads
  per inch
• So for our screwdriver
• MA 3.14/0.1 31.4

Circumference ? x 1 3.14 Pitch 1/10
0.1
16
Wedge

• An inclined plane on its side
• Used to cut or force material apart
• Often used to split lumber, hold cars in place,
  or hold materials together (nails)

17
Mechanical Advantage Wedge

• Much like the inclined plane, the mechanical
  advantage of a wedge is the length of the slope
  divided by the width of the widest end
• So for our wedge,
• MA 6/2 3
• They are one of the least efficient simple
  machines

18
Pulley

• A rope or chain free to turn around a suspended
  wheel
• By pulling down on the rope, a load can be lifted
  with less force
• Trade off no real trade off here the secret is
  that the pulley lets you work with gravity so you
  add the force of your own weight to the rope

19
Mechanical Advantage Pulley

• The Mechanical Advantage of a pulley is equal to
  the number of ropes supporting the pulley
• So for the pulley system shown there are 3 ropes
  supporting the bottom pulley
• MA 3
• This means that if you pull with a force of 20
  pounds you will lift an object weighing 60 pounds

20
The trick is WORK

• Simple machines change the amount of force
  needed, but they do not change the amount of work
  done
• What is work?
• Work equals force times distance
• W F x d
• By increasing the distance, you can decrease the
  force and still do the same amount of work

21
Examples

• Lever
• Work is equal on both sides of a lever. You move
  the long end a LARGE distance with SMALL force.
  The other end moves a SMALL distance with a LARGE
  force, which is why it can lift heavy objects.

• Inclined Plane
• It takes a certain amount of work to get the
  cabinet into the truck. You can either exert a
  LARGE force to lift it the SMALL distance into
  the truck, or you can exert a SMALL force to move
  it a LARGE distance along the ramp.

22
Efficiency

• The efficiency is a ratio that measures how much
  work the machine produces versus
• how much work goes in
• Example We have an inclined plane
• with an ideal MA of 3. We measure
• our real-life inclined plane and find
• an MA of 2.
• Efficiency Actual MA/Ideal MA x 100
• (2/3) X 100
• 66.66

23
Sources
COSI.org. 2006. Simple Machines. Accessed 3
February 2006. http//www.cosi.org/onlineExhibits
/simpMach/sm1.html Jones, Larry. January 2006.
Science by Jones Levers. Accessed 2 February
2006. http//www.sciencebyjones.com/secondclassle
vers.htm Mikids.com. 2006. Simple Machines.
Accessed 2 February 2006. http//www.mikids.com/S
machines.htm Professor Beakers Learning Labs.
August 2004. Simple Machines inclined planes.
Accessed 2 February 2006. http//www.professorbea
ker.com/planefact.html Wikepedia. Accessed 3
February 2006. http//en.wikipedia.org/wiki/Mecha
nicaladvantage