Download machines. S8P3c: Demonstrate the effect of simple

GPS Standards
S8CS5a: Observe and explain how parts can be
related to other parts in a system such as the
role of simple machines in complex (compound)
machines.
S8P3c: Demonstrate the effect of simple machines
(lever, inclined plane, pulley, wedge. screw, and
wheel/axle) on work.
What Are Machines?
A
machine is a tool used to make
work easier.
A
simple machine is a machine
that has very few moving parts
There are six types of
simple machines:
- inclined plane
- wedge
- wheel and axle
- screw
- pulley
- lever
Compound machines have two or
more simple machines working
together to make work easier
All compound machines are
made of these simple machines
Examples of Compound
Machines
Work

Work is defined as a force acting on an
object to move it across a distance.

Pushing, pulling, and lifting are common
forms of work.

Work involves 2 things: Force and
Distance
Formula: Work = force (f) x distance (d)
Work Smarter NOT Harder

According to the Law of Conservation of
Energy: the amount of work put into a
machine equals the amount of work that
comes out
Work Input = Work Output
So how can machines make work easier?
GPS Standards
S8CS5a: Observe and explain how parts can be
related to other parts in a system such as the
role of simple machines in complex (compound)
machines.
S8P3c: Demonstrate the effect of simple machines
(lever, inclined plane, pulley, wedge. screw, and
wheel/axle) on work.
Advantages of Using Simple
Machines to do Work
Simple Machines change :
• the size of the force
• the direction of the force
• the distance through which the force
moves.
Advantages of Using Simple
Machines to do Work
Simple Machines can change the direction
of the force
Input
force
Output
force
Advantages of Using Simple
Machines to do Work


Simple Machines can multiply the force
thus changing its size, but the distance
must also increase
It’s a trade off!
The amount of work stays the same.
Takes more force to lift
but less distance
Takes less force to roll
but longer distance
Effort and Resistance Force


The effort force is the force that a person
would put into the machine to move the
object
The resistance force is the force exerted
by the load (the thing to be moved) in
resistance to the effort
Mechanical Advantage (MA)

How much easier and faster a machine
makes your work is the mechanical
advantage of that machine.

In science terms, the mechanical
advantage is the number of times a
machine multiplies your effort force.
Mechanical Advantage (MA)

To find the MA of a machine, you can
divide the resistance force (output) by
the effort force (input).

Most of the time the resistance force is
the weight of the object in Newtons.

Formula: MA = FR / FE
(FR = resistance force ; FE = effort force)
ALL SIMPLE MACHINES HAVE A
MECHANICAL ADVANTAGE
THAT HELPS US TO DO WORK
Inclined Plane





A plane is a flat surface.
When a plane is inclined, or slanted, it can
help you move objects across distances.
A common inclined plane is a ramp.
Lifting a heavy box onto a loading dock is
much easier if you slide the box up a ramp (an
inclined plane)
You trade a larger force for a longer distance
Takes more force to lift
but less distance
Takes less force to roll
but longer distance
MA of an Inclined Plane

To find the MA of an inclined plane,
divide its length by its height.
MAI = length / height
MAI = 12m / 6m
MAI = 2
Calculate the MAI
MAI = length / height
MAI = 3000m / 100m
MAI = 30
Wedges




A wedge is a modification of an inclined plane
that moves.
It is made of two inclined planes put together.
Instead of the resistance being moved up an
inclined plane, the inclined plane moves the
resistance.
It changes the direction of the force
MA of a Wedge

The mechanical advantage of a wedge
can be found by dividing the length of
either slope (s) by the thickness (t) of
the big end

MAW = S (slope) / T (thickness)
Screw

A screw is an inclined
plane wrapped around
a post.
Thread
Screw
MA of a Screw




The distance between two adjacent screw
threads is called the pitch of a screw.
One complete revolution of the screw will
move it into an object a distance equal to the
pitch of the screw.
The mechanical advantage of a screw can be
found by dividing the circumference of the
screw by the pitch of the screw.
This formula is shown below:
MAS = Circumference / Pitch
LEVERS
A lever is an arm that "pivots" (or
turns) against a "fulcrum" (or point).
Parts of a Lever

FULCRUM
The fixed pivot point of a lever

EFFORT ARM
The part of a lever to which force is applied

RESISTANCE ARM
The part of the lever that bears the load or
resistance

LOAD
The object to be moved or the resistance to be
overcome in order for work to be accomplished
Parts of a Lever
FIRST CLASS
SECOND
CLASS
Examples of this
kind of lever are : the pry bar, seesaw, hammer and pliers
An example
of this kind of lever is :
the wheelbarrow and bottle
opener .
An example of this kind of lever
is : fishing rod
THIRD CLASS
They can be remembered by what is in the
middle
MA of a Lever

To find the MA of a lever, divide the effort
arm length by the resistance arm length.
MAL = effort arm length/resistance arm length
• A pulley is a rope or chain
wrapped around a grooved
wheel.
• A single pulley simply
reverses the direction
of a force.
Pulleys
Input
force
output
force

When two or more pulleys are connected
together, they allow a heavy load to be lifted with
less force.

The trade-off is that the end of the rope must
move a greater distance than the load
Types of Pulleys

Fixed Pulleys - pulleys attached to stationary
structures

A moveable pulley rises and falls with the load that
is being moved. A single moveable pulley creates
a mechanical advantage; however, it does not
change the direction of a force.

Pulleys can also multiply force. If you attach the
pulley to the object that you are moving, the object
will move one meter for every two meters the force
pulls.

A compound pulley is a moving pulley with a fixed
pulley attached to it.
MA of a Pulley

The mechanical advantage of a pulley is
equal to the number of ropes that support
the pulley.
Wheel and
Axle
• A wheel and axle is a modification
of a pulley.
• It is a disk fixed to a shaft. The wheel
and shaft must move together to be a
simple machine.

Sometimes the wheel has a
crank or handle on it.
Examples of wheel and axles
include roller skates and doorknobs
Examples of Items using a Wheel
and Axle
MA of a Wheel and Axle

The mechanical advantage of a wheel
and axle is the ratio of the radius of the
wheel to the radius of the axle.

If the radius of the wheel is four times
greater than the radius of the axle,
every time you turn the wheel once,
your force will be multiplied four times
MAWA = Radius of wheel : Radius of axle
Mechanical Advantage (cont’)

In the wheel and axle illustrated below, the
radius of the wheel is five times larger than
the radius of the axle. Therefore, the
mechanical advantage is 5:1 or 5
Machine Efficiency

All machines waste some energy overcoming friction.

Efficiency compares the output work to the
input work.

The less friction there is to overcome, the
closer output work is to input work (the
more efficient the machine is).
Machine Efficiency con’t.

Efficiency is expressed as a percent (%).

Formula:
output work
input work
x 100
Sample Problem:
A person does 1,500 J of work with a
hammer. The hammer does 825 J of work on
a nail, what is the efficiency of the hammer?
The Answer
Efficiency = output
input
x 100
Efficiency = 825J x 100
1500J
Efficiency = (0.55) x 100 = 55%