Transcript Document

Simple Machines
What is a Simple Machine?

A simple machine
has few or no
moving parts.
 Simple machines
make work easier
Wheels and Axles

The wheel and axle
are a simple
machine
 Gears are a form of
wheels and axles
Pulleys

Pulley are wheels
and axles with a
groove around the
outside
 A pulley needs a
rope, chain or belt
around the groove
to make it do work
Inclined Planes

An inclined plane is
a flat surface that is
higher on one end
 Inclined planes
make the work of
moving things easier
Wedges
Two inclined
planes joined
back to back.
 Wedges are used
to split things.

Screws
A screw is an
inclined plane
wrapped around a
shaft or cylinder.
 The inclined plane
allows the screw
to move itself
when rotated.

Levers-First Class

In a first class lever
the fulcrum is in the
middle and the load
and effort is on
either side
 Think of a see-saw
Levers-Second Class

In a second class
lever the fulcrum is
at the end, with the
load in the middle
 Think of a
wheelbarrow
Levers-Third Class

In a third class lever
the fulcrum is again
at the end, but the
effort is in the
middle
 Think of a pair of
tweezers
Simple Machines

Simple Machines
can be put together
in different ways to
make complex
machinery
Simple Machines- Mechanical
Advantage
 Mechanical
advantage (MA) is the ratio
of the force put into the machine (Effort
Force) to the force the machine exerts
on an object (Resistance Force).
 MA = Fr / Fe
 MA
> 1 means that the machine makes
work easier and increases the amount of
force applied
A sample problem
A
worker uses a pulley to lift a 45 kg
object. If the mechanical advantage of
the pulley is 5.2, what is the effort force
exerted by the worker?
MA = Fr / Fe
Effort Force = ???
Mass = 45 kg
Resistance Force = 45 * 9.8 = 441 N
5.2 = 441 N / Fe
Effort Force = 85 N
A sample problem – You try it
A
worker uses a lever to lift an object
with a mass of 3500 N. If the force
applied by the operate was 1500 N,
what is the mechanical advantage of the
lever?
MA = Fr / Fe
Effort Force = 1500 N
Resistance Force = 3500 N
MA = 3500 N / 1500 N
MA = 2.33
Simple Machines – Ideal
Mechanical Advantage
 Ideal
Mechanical advantage is the ratio
of distance moved by the person (de ) to
the distance the machine moved the
object (dr ).
 IMA = de / dr
LOOK AT PAGE 266 Figure 10-9
A Sample Problem- You Try it
A
worker testing a multiple pulley
system to estimate the heaviest object
the system could move. When the
worker moves the rope 1.5 m, the object
moves 0.25 m. What is the IMA of the
system?
IMA = de / dr
Simple Machines - efficiency
 Efficiency
is the ratio of work output
(Wo) to work input (Wi ) multiplied by
100.
 Efficiency
= e = (Wo / Wi ) *100
 Another
way to calculate it using
mechanical and ideal mechanical
advantage
 Efficiency
= e = (MA / IMA) * 100
A sample problem
A
man exerts a force of 310 N on a
lever to raise a crate with a mass of
910 kg. If the efficiency of the lever is
78%, what is the lever’s IMA?
e = (MA / IMA) * 100
IMA = de / dr
Effort Force = 310 N
Mass = 910 kg
Resistance Force = 910 * 9.8 = 8910 N
MA = 8910 / 310
MA = 28.7
MA = Fr / Fe
e = (MA / IMA) * 100
78 = (28.7 / IMA) *100
IMA = 36.8
A sample problem – You Try It
A
man exerts a force of 650 N on a
lever to raise a crate with a weight of
1000 N. If the efficiency of the lever is
55%, what is the lever’s IMA?
e = (MA / IMA) * 100
Effort Force = 650 N
Resistance Force = 1000 N
MA = 1000 / 650
MA = 1.53
IMA = de / dr
MA = Fr / Fe
e = (MA / IMA) * 100
55 = (1.53 / IMA) *100
IMA = 2.8
Homework
 Page
280
 Problems:
79-84