Key Questions:
 What is a newton?
 How does a lever work?
 What is the relationship
between force and distance in
a simple machine?
 What factors balance a lever?
Performance Objectives
 Describe how a lever works.
 Identify the relationship between force
and distance on a lever.
 Apply the concept of mechanical
advantage to levers.
Lever Assembly
 SAFETY NOTE:
 WATCH for FALLING weights on
bare toes or sandals or table tops!
 DO not place the fulcrum higher
than hole 3 of stand!
FORCES
 Forces have two important properties:
strength (magnitude) and direction.
 In the English system of units, the
strength of a force is measured in
pounds.
 When you measure your own weight in
pounds, you are measuring the force of
gravity acting on your body.
The NEWTON
 In the metric system, the strength
of a force is measured in newtons
(N).
 A quarter-pound hamburger has a
weight of about 1 newton (1 lb =
4.448 N).
Zero the Spring Scale
 In the metric
system, the
strength of a
force is
measured in
newtons (N).
Gravity and weight

The force of gravity on an object is called
weight.

Mass and weight are not the same thing!
Gravity and weight

A 10-kilogram rock has a
mass of 10 kilograms no
matter where it is in the
universe.

A 10-kilogram rock’s
weight however, can vary
greatly depending on
where it is.
Simple Machines
 A simple machine is an unpowered
mechanical device, such as a lever.
 Simple machines change the
magnitude or direction of forces
Introducing… The
Lever
 A lever includes a stiff structure (the lever)
that rotates around a fixed point called the
fulcrum.
fulcrum
Anatomy of the lever
 Fulcrum – point around which the lever
rotates
 Input Force – Force exerted ON the lever
 Output Force – Force exerted BY the lever
CPO Lever – First Class All The Way
 Here we have a first class lever.
 The fulcrum is between the input and output.
 Can you get two weights to balance?
Levers in
Equilibrium
 Hang your weights like shown here.
 Does the lever balance?
 What variables can be changed to
balance a lever?
Four Variables in a Lever
 Amount of Input Force
 Amount of Output Force
 Length of Input Arm
 Length of Output Arm
Lever Challenge
 Hang weights from
the lever and get it to
balance.
 Use only 3 strings,
one string per
position and string
MUST have weight.
 Do 4 trials and
record how many
weights to hang and
where you hang
them.
Lever Challenge
Lever Concept
 Hang 1 weight 10
cm from the
fulcrum.
 Where does the
output force need
to be to oppose
our input force?
1
1
Basic Lever Investigation
 If we move the
input force 10 cm,
how much more
do we need to
add for the same
output force?
 Try it...
1
Basic Lever Investigation
 If we move the
input force 10
more cm, how
much more do we
need to add for
the same output
force?
 Add two masses
at 20 cm.
1
Mathematical Rule for
Balancing the Lever
 What mathematical relationship can you
find that will balance the lever every time?
 Put your rule in terms of input and output
and forces and distances.
 What if there is more than one location on
either side of the lever?
What is the Relationship?
Input Force
x Length of
Input Arm
=
Output Force
x Length of
Output Arm
Force x Distance = Force x Distance
# of Weights
x Distance
=
# of Weights
x Distance
What if there several groups of
weights ?
Sum of Input = Sum of Output
(F1 x D1) + (F2 x D2)
=
(F3 x D3) + (F4 x D4)
TOY Engineers
 Allow time for students to brainstorm
possible design ideas and to plan how
they will construct their toys.
 Once students have built their toys, let
them share their creations with the
class.
Outcomes
 Use science
 Think scientifically
 Communicate technical ideas
 Teach all students
 Be science conscious NOT
science phobic
What questions do you
have about the CPO
Levers?