Simple Machines and Mechanical Advantage

Machine– is an instrument that makes work EASIER.

Rube Goldberg Creations

Passing man (A) slips on banana peel (B) causing him to fall on rake (C). As handle of rake rises it throws horseshoe (D) onto rope (E) which sags, thereby tilting sprinkling can (F). Water (G) saturates mop (H). Pickle terrier (I) thinks it is raining, gets up to run into house and upsets sign (J) throwing it against non-tipping cigar ash receiver (K) which causes it to swing back and forth and swish the mop against window pane, wiping it clean. If man breaks his neck by fall move away before cop arrives.

Rube Goldberg

Honda Commercial

http://www.boardsmag.com/screeningroom/commercials/581

Simple Machines and Work2 types of work involved with machines:

1. Work input– the work that goes INTO the machine

WORK INPUT = Effort Force X Effort Distance

Effort Force is the force applied TO the machine.(usually what YOU apply to the machine)

Effort Distance is the distance over which you apply force.

Simple Machines and Work2. Work Output– the work done by the MACHINE

WORK OUTPUT = Resistance Force X Resistance Distance

Resistance Force is usually the weight of the object being moved.

Resistance Distance is the distance the object is moved EVEN if there was no machine.

IMPORTANT!

Machines DO NOT INCREASE the work put into them, they just make work easier.

Allows you to use

less force!!!

Mechanical Advantage

Mechanical Advantage: how many times the machine multiplies your effort force.

how much the machine REDUCES how much effort force you have to apply.

What you lose in EFFORT FORCE, you gain in EFFORT DISTANCE.

Mechanical AdvantageExample:If you are using a machine that has a mechanical

advantage of 2.5,you will have increased your EFFORT DISTANCE by 2.5 times.

This allows you to REDUCE the EFFORT FORCE needed by 2.5 times.

Mechanical AdvantageIdeal Mechanical Advantage (IMA)= Assumes that there is NO FRICTION

involved.

IMA = Effort Distance/ Resistance Distance

or

Resistance Force/ Effort Force

Ed / Rd or Rf / Ef

6 Types of Simple Machines

1. Inclined Plane

2. Wedge

3. Screw

4. Lever

5. Wheel and Axle

6. Pulley

All are forms of inclined planes

Inclined Plane

A flat slanted surface

Ef

The weight of the box is the Rf

Rf

RdEd

Inclined Plane IMA

3 meters1.5

me

ter

Box weighs250 N

IMA = Ed / Rd 3m / 1.5m = 2

or

IMA = Rf / Ef 250/ ??? =

IMA

Ed

RdIMA

Rf

Ef

Inclined Plane and Work

3 meters1.5

me

ter

Box weighs250 N

Work = Force X Distance

•Use either: Resistance Force and Resistance Distance OR

Effort Force and Effort Distance

Work = Rf x Rd 250 N X 1.5m = 375 Joules

Wedge

A moving inclined plane

The longer and thinner the Wedge (inclined plane), the higherThe IMA. (the better the machine)

IMA of a Wedge

Calculate the IMA of eachInclined plane and add together.

6 cm 6 cm

10 cm10

cm

Ed/ Rd 10/6 = 1.67

10/6 = 1.67 _______ 3.34

IMA is 3.34

A wedge is 2 inclinedPlanes together.

Screw

An inclined plane wrapped around a central bar to form a spiral

IMA of a ScrewHigher IMA, MORE THREADS

Lower IMA, less threads

With more threads, turn the screw for a LONGER DISTANCE so can use LESS FORCE.

Lever

Rigid bar that is free to pivot about a fixed point.

Fulcrum: the fixed point on a lever.

Classes of LeversRf

Rf

Rf

force

force

force

________

_______

_______

Effort DISTANCE = Effort ARM •from the fulcrum to the point of Effort force.

Resistance DISTANCE = Resistance ARM•From the FULCRUM to the point of Resistance force

1st Class F2nd Class R3rd Class E

1st Class Lever

Changes direction of the force

Rf

Ef

Rf

Ef

Ef

Rf

2nd Class Lever

Rf

Ef

3rd Class Lever

Does not multiply youreffort force, It just makes it a little easier (or increases speed)

Levers and IMA

What is the IMA of the following lever?

What kind of lever is it?

300 N

Ef

2 m

.25 m

Levers and IMA

. 5 m2.5 m

Ef = 60 N

What is the IMA of the hockey stick?

What type of lever is the hockey stick?

Rf

Wheel and Axle

•Made up of 2 circular objects of different sizes

Wheel– the large circle•Effort distance

Axle– the smaller circle.•Resistance Distance

Wheel and Axle

Wheel and Axle and IMA24

cm

6 cm

What is the IMA?

Ed/Rd

Pulley A rope, belt or chain wrapped around a

grooved wheel.

Type of Pulleys

Fixed Pulley: pulley attached to a structure. Changes the direction of the Effort Force DOES NOT multiply your effort force

Calculate IMA by counting the number of SUPPORTING ropes.

IMA = 1

Types of Pulleys

Movable Pulley: attach pulley to a moving object

IMA = 2

•Multiplies force, but does not change direction

Compound Pulleys Combination fixed and movable pulleys

IMA =

IMA =

Examples of Pulleys

Examples

Block and Tackle System

I guess that’s It! Whew!

Any Questions?