6 Simple Machines
Every complex machine is made of these:
1.
2.
3.
4.
5.
6.
The inclined plane (ramp)
The wedge (sharp point)
The screw (grooved)
The lever (arm & fulcrum)
The wheel and axle (turns on itself)
The pulley (ropes)
Which simple machine are these?
h simple machine is this
device used for boring holes
Which simple machines
do you see?
Plane, wheel/axle, lever
Which simple machines are
being used together?
Wedge, lever
Machines help in 3 ways:
1. Change amount of force needed
2. Change distance you push/pull
3. Change direction of your force
Machines hurt in 1 way:
always more actual work since
most also overcome friction!
*Mechanical Advantage (MA)
The number of times a
machine multiplies your effort force (Fin)
MA = Fout/ Fin
(wt of object / your force)
MA > 1 means you use less force
MA < 1 means you use more force
IMA = din/dout (distance you push, distance wt moves)
Real MA includes friction, always less than ideal
Ideal MA (IMA) uses only geometry, max possible
* real ma also known as actual MA or AMA*
Reality check!
Can a machine make it easier for
you in two ways
- less force, and less distance?
Can a machine save you work?
Can IMA be less than actual MA?
(
a
l
L
n
o
!
)
IMA- Based only on what you see
not what you measure!
Pulley: IMA = #ropes – 1 pull down
ramp: IMA= length/height
Lever:
IMA = ratio of lever arms
Just for fun…..
Screw: IMA= # turns/inch
Wedge: IMA= angle related
Wheel/axel: IMA: ratio of gear sizes
Pulley: change direction or force
► Ideal
Mechanical advantage (IMA)
= # strings supporting weight
(don’t count one you grab and pull down)
(do count if you grab and pull up)
IMA= 1
IMA= 2
Pulley examples
IMA= __ ___
___
___
Inclined Plane
Why build longer, shallow ramps
instead of short, steep inclines?
►
►
A wagon trail on a steep
hill will often traverse back
and forth to reduce the
slope experienced by a
team pulling a heavily
loaded wagon.
This same technique is
used today in modern
freeways which travel
winding paths through
steep mountain passes.
more distance, less force!
Levers (3 types)
► 1st
Class: teeter-totter
IMA > 0
► 2nd
class Lever:
(wheel barrel)
IMA > 1
Output
force
Output force
Input
force
Input
force
Input
force
Output
force
► 3rd
class: joints
IMA < 1
Distance from fulcrum to input force
Ideal MA =
Distance from fulcrum to output force
There are 3 classes of levers.
First class lever
Changes the
direction of the
force
Multiplies effort
force
Magnifies speed
and distance
Ex: seesaw,
crowbar, scissors
There are 3 classes of levers.
Second class lever
Multiply effort force
Mechanical
advantage is
always greater
than 1.
Ex: bottle opener,
boat oars, wheel
barrow
There are 3 classes of levers.
Third class lever
Magnifies speed
and distance
Mechanical
Advantage always
less than 1
Ex: baseball bat,
golf club, broom
Which type of lever is this?
Is IMA > 1, =1, or < 1
Which type of lever is this?
Is IMA > 1, =1, or < 1
Efficiency
►
►
Ideally, a machine is 100% efficient:
your work (in)
Win
Fin * din
If Re-arrange :
=
=
=
machine’s work (out)
Wout
Fout * dout
Fout / Fin = din / dout = IMA
However, some output force is lost due to friction.
►
efficiency = (work out / work in ) * 100
►
Using a machine may reduce force or distance, but not work!