Transcript Powerpoint Detroit INS Levers

Integrated Natural Science
Integrated Natural
Science
for
Detroit Public Schools
Levers
Kat Woodring
Key Questions:
 4.2.1 Analyze and label the parts of a lever and
evaluate how a lever multiplies force.
 4.2.2 Provide examples of first, second and third
class levers.
 4.2.3 Compare parts of the human body to the types
of levers.
 4.2.4 Calculate and determine the mechanical
advantage of a lever.
District Outcomes
 Qualitatively and quantitatively explain
forces and charges in motion.
 Observe and explain forces as push and
pull, acting on an object and exerted by
the object.
 Analyze the operations of machines in
terms of force and motion.
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!
4.1 Forces in Machines
 A simple machine is an unpowered
mechanical device, such as a lever.
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
Levers and the human body
 Your body contains
muscles attached to
bones in ways that
act as levers.
 Here the biceps
muscle attached in
front of the elbow
opposes the
muscles in the
forearm.
Can you think of other muscle
levers in your body?
Three Classes of Levers
 First Class - fulcrum
between Input and output
 Second Class – output
between fulcrum and input
 Third Class – input
between fulcrum and
output
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 at least 3
strings!
 Do 4 trials and
record how many
weights to hang and
where you hang
them.
Lever Challenge
Lever Modification
 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.
 HINT: you will need
two strings
1
Basic Levers Investigation
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)
Mechanical Advantage
We use the same kind of relationship for
all simple machines to calculate
Mechanical Advantage.
Output Force / Input Force
4.1 Mechanical Advantage
mechanical
advantage
Input force (N)
MA = Fo
Fi
Output force (N)
Michigan Content Expectations
 P4.1c Explain why work has a more precise
scientific meaning than the meaning of work in
everyday language.
 P4.1d Calculate the amount of work done on an
object that is moved from one position to another.
 P4.1e Using the formula of work, derive a formula
for change in potential energy of an object lifted in
a distance h.