integrated natural science. for detroit public schools levers kat woodring
TRANSCRIPT
Integrated Natural Science
Integrated Natural Science
for Detroit Public
Schools
LeversKat 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 Equilibriu
m
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?
Force x Distance = Force x Distance
Input Force
x Length of Input Arm
# of Weights x Distance
Output Force
x Length of Output Arm
=
# 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
MA = Fo
Fi
Output force (N)
Input force (N)
mechanicaladvantage
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.