2. 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.
3. 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)
4. Lever Systems Continued
Effort Arm – The part of the lever to which the effort
force is applied.
Definitions Continued
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.)
5. Parts of a Lever System
A. Lever E. Effort Arm
B. Fulcrum H. Resistance ArmF. Effort Force
C. Resistance Distance
D. Resistance Force
G. Effort Distance
Entire board
C
D
H
G
F
B
A
E
21. Lever Force and Mechanical
Advantage Formulas
Mechanical Advantage = Effort Distance / Resistance Distance
Effort Distance = Mechanical advantage x Resistance Distance
Resistance Distance = Effort Distance / Mechanical
Advantage
MA = Ed / Rd
Ed = MA x Rd
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.
22. Effort Force Needed
Effort Force = Resistance Force / Mechanical advantage
EF = 120 N / 3
EF = _______
Mechanical Advantage = Effort Distance / Resistance Distance
MA = 3 / 1 = 3
40 N
23. Lever Force and Mechanical
Advantage Formulas
Effort Force = Resistance Force / Mechanical Advantage
Resistance force = Effort Force x Mechanical advantage
Mechanical Advantage = Resistance Force / Effort Force
Ef = Rf / MA
Rf = Ef x MA
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.
29. You Try!
?
MA = 1 Rf = 60N
What is the only advantage to this lever system?
It changes direction of motion.
Rf = Ef x MA
30. 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.
31. 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.
