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Lever Systems
Lever systems Objectives:
1. Identify the three types of levers.
2. Label a lever system with appropriate part
indications:
3. Determine the mechanical advantage of various
lever systems.
4. Identify the effect of friction on an object when it is
being moved.
5. Communicate using correct science terminology
when discussing lever systems in general and
specific terms.
Lever Systems
Definitions
Lever – A bar that is free to pivot around a center point
(Changes direction and/or amount of force).
Fulcrum – The fixed point around which a lever pivots
(fulcrums can take many shapes).
Effort Force – The force applied to a machine to cause
motion of an object. (Measured in Newtons N)
Resistance Force – The force exerted by an object due
to gravity or friction. (Measured in Newtons N)
Mechanical Advantage – The number of times a
machine multiplies the effort force.
(MA = Ed/Rd)
Lever Systems Continued
Definitions Continued
Effort Arm – The part of the lever to which the effort
force is applied.
Effort Distance – The length of the part of the lever
from the fulcrum to the effort end of the lever.
(The length of the Effort Arm.)
Resistance Arm – The part of the lever on which the
resistance force is exerted.
Resistance Distance - The length of the part of the
lever from the fulcrum to the resistance end of
the lever. (The length of the Resistance Arm.)
Parts of a Lever System
A. Lever
C. Resistance Distance
B. Fulcrum D. Resistance Force
E. Effort Arm
G. Effort Distance
F. Effort Force H. Resistance Arm
F
G
C
E
D
A
H
Entire board
B
Classes of Levers
Effort
Resistance
Fulcrum
First Class Lever
Classes of Levers
Effort
Resistance
Fulcrum
Second Class Lever
Classes of Levers
Effort
Resistance
Fulcrum
Third Class Lever
You Label!
Second Class Lever
E
R
F
You Label!
First Class lever
E
R
F
You Label!
Third Class Lever
E
R
F
Classes of Levers Examples
Third Class Lever
R
E
F
Classes of Levers Examples
R
F
E
First Class Lever
Classes of Levers Examples
First Class Lever
Classes of Levers Examples
Third Class Lever
Classes of Levers Examples
Second Class Lever
R
F
E
Classes of Levers Examples
Second Class Lever
of Levers Examples
Classes ofClasses
Levers
Examples
Classes of Levers Examples
First Class Lever
Mechanical Advantage
Mechanical Advantage = Effort Distance / Resistance Distance
MA = 3 / 1 = 3
Lever Force and Mechanical
Advantage Formulas
Mechanical Advantage = Effort Distance / Resistance Distance
MA = Ed / Rd
Effort Distance = Mechanical advantage x Resistance Distance
Ed = MA x Rd
Resistance Distance = Effort Distance / Mechanical Advantage
Rd = Ed / MA
These formulas are all dirivations of the first formula. If you know
your Algebra you should be able to solve for any of the individual
parts of each equation if the other two parts are known.
Effort Force Needed
Mechanical Advantage = Effort Distance / Resistance Distance
MA = 3 / 1 = 3
Effort Force = Resistance Force / Mechanical advantage
EF = 120 N / 3
40 N
EF = _______
Lever Force and Mechanical
Advantage Formulas
Effort Force = Resistance Force / Mechanical Advantage
Ef = Rf / MA
Resistance force = Effort Force x Mechanical advantage
Rf = Ef x MA
Mechanical Advantage = Resistance Force / Effort Force
MA = Rf / Ef
These formulas are all dirivations of the first formula. If you know
your Algebra you should be able to solve for any of the individual
parts of each equation if the other two parts are known.
Mechanical Advantage
Effort Distance
Resistance Distance
MA = Ed / Rd = 100 cm / 50 cm = 2
Your Try!
?
Rf = Ef x MA
MA = 4
Rf = 40g
You Try!
?
Rf = Ef x MA
MA = 6
Rf = 540N
You Try!
?
Rf = Ef x MA
MA = 2
Rf = 120N
You Try!
?
Ef = Rf / MA
MA = 3
Rf = 10N
You Try!
?
Rf = Ef x MA
MA = 1
Rf = 60N
What is the only advantage to this lever system?
It changes direction of motion.
Effect of Pulling Up, Down, Or
Straight
Three Kinds of Friction
Sliding Friction –Two surfaces sliding against each other.
Rolling Friction – one surface rolls over another surface.
Fluid Friction – When a lubricant is used between to objects that
are sliding over each other.
Lever systems Objectives:
1. Identify the three types of levers.
2. Label a lever system with appropriate part
indications:
3. Determine the mechanical advantage of various
lever systems.
4. Identify the effect of friction on an object when it is
being moved.
5. Communicate using correct science terminology
when discussing lever systems in general and
specific terms.