Simple Machines
Why are machines useful and how
do they relate to what he have
been discussing about energy?
Simple Machines
A machine is a devise used to either change a force or
redirect a force.
These machines (whether you notice them or
not) are involved in every activity that you
participate in.
The reason for this is that they range from the
very complicated machines you generally think
of when you think of a factory assembly line, to
individual joints in the human body.
Simple Machines
There are a number of different types of simple machines,
all of which work on the same principle: doing work
Some types of simple machines:
Pulleys
Levers
Ramps
Simple Machines
We know:
W  F d
By changing your input distance you can in turn change your
input force.
The key to any simple machine is that regardless of
how you change this input force or distance, the work
you put into a task will be equal to the work you get out
of it
Simple Machines
All of these machines can be used to change either an input
or output force based on how much YOU move.
In general a machine is useful because it allows you to input
less force to move something that requires a greater amount
of force.
The trade off for this is that, in order to allow you to push
softer, you must move farther. Take for example….
Levers
A lever is a machine that has 3 major parts:
Resistance
(Resistive force)
(Load)
Fulcrum
Input Force
(Effort)
You can change what effort you put into a task by changing
the distance you must move during that effort.
Levers
The work done on one side of the fulcrum must be equal to
the work done on the other side NO MATTER WHAT!
200 N
200 N
Fd = Fd
Levers
work input = work output
F
d
d
F
(force x distance)input = (force x distance)output
Mechanical Advantage
80 N
F
1m
d
d
10 N
____ m
F
Mechanical Advantage = (Foutput)/(Finput) = 80/10 = 8
Type 1 Lever
(1st class)
First-class levers have the fulcrum placed between
the load and the effort, as in the seesaw, crowbar, and
balance scale.
Type 1 Lever
(1st class)
Gluteus Medius
(Lifting a leg, stabilizing hips
or shifting weight)
Type 2 Lever
(2nd class)
Second-class levers have the load between the effort and
the fulcrum. A wheelbarrow is a second-class lever.
Type 2 Lever
(2nd class)
Type 3 Lever
(3rd class)
Third-class levers have the effort placed between the
load and the fulcrum. The effort always travels a
shorter distance and must be greater than the load.
Type 3 Lever
(3rd class)
This is the most common type of lever utilized by the
human body.
Levers Question
What is the mechanical advantage of a 1st class lever
whose fulcrum is closer to the load? The load has a weight
of 400 N and moves a distance of 0.2m. You move your end
of the lever 1 meter.
Pulleys
A system of pulleys can be used to either change the direction
of a force or change the input force to move a load.
*MA = Mechanical Advantage
Pulleys
You can change the mechanical advantage of a pulley system
by changing the complexity of the pulley system
MA = 1
MA = 2
For the second situation, you must pull a length of rope twice
the magnitude that the load gets lifted. (Because work is
equal on both ends)
Ramps
(Inclined Planes)
By increasing the distance that you move a load, you can
decrease the force you must input to lift it to a specific
height.
Ramps
(Inclined Planes)
d
d
Efficiency
efficiency =
efficiency =
actual mechanical advantage
theoretical mechanical advantage
Output Work (Wout)
Input Work (Win)