Lever Systems

By Marvin Lowe

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

DefinitionsLever – 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

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.)

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

CD

H

GF

B

A

E

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!

R

F

E

Second Class Lever

You Label!

R

F

E

First Class lever

You Label!

R

E

F

Third Class Lever

Classes of Levers Examples

F

E

RThird Class Lever

Classes of Levers Examples

E

F

R

First Class Lever

Classes of Levers Examples

First Class Lever

Classes of Levers Examples

Third Class Lever

Classes of Levers Examples

F

ER

Second Class Lever

Classes of Levers Examples

Second Class Lever

Classes of Levers ExamplesClasses of 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

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.

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

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.

Mechanical Advantage

Effort Distance

Resistance Distance

MA = Ed / Rd = 100 cm / 50 cm = 2

Your Try!

?

MA = 4 Rf = 40g

Rf = Ef x MA

You Try!

MA = 6 Rf = 540N

?

Rf = Ef x MA

You Try!

?

MA = 2 Rf = 120N

Rf = Ef x MA

You Try!

?

MA = 3 Rf = 10N

Ef = Rf / MA

You Try!

?

MA = 1 Rf = 60N

What is the only advantage to this lever system?

It changes direction of motion.

Rf = Ef x MA

Effect of Pulling Up, Down, Or Straight

Three Kinds of FrictionSliding 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.