CONSTRUCTIVE THOUGHTS Simple Machines 7.2. Six Types of Simple Machines leverpulley wheel and axle inclined plane screwwedge.

CONSTRUCTIVETHOUGHTS

Simple MachinesSimple Machines

7.27.2

Six Types of Simple

Machines

leverlever

pulleypulley

wheel and axlewheel and axle

inclined planeinclined plane

screwscrew

wedgewedge

Lever

• A bar free to pivot about a fixed point

• fulcrum = fixed point• effort arm = part of lever where

Fe is applied

• resistance arm = part of lever where Fr is applied

The Mechanical Advantageof Levers

• MAlever =

length of effort arm (Le)

length of resistance arm (Lr)

• Problem:A worker uses an iron bar to raise a manhole cover weighing 65 N. The effort arm of the lever is 60 cm long, and the resistance arm is 10 cm long. What is the MA of the bar?

• First class: multiply force and/or direction

• Second class: multiply force

• Third class: cannot multiply force; MA < 1 = increases speed

Three Types of Levers

R E

F

R E

F

RE

F

Examples of Class Three Levers

Pulley

• grooved wheel with rope/chain running along groove

• fixed or movable:– fixed: changes direction; MA = 1– movable: multiplies force; MA = 2

»block and tackle: system of fixed and movable pulleys

Wheel and Axle

• 2 wheels of different sizes that rotate together– Fe applied to larger wheel– smaller wheel (axle) exerts Fr

• MA = radius of wheel (rw)

radius of axle (ra)»Problem: A steering wheel

with a 24 cm radius turns the column with a 4 cm radius. What is the MA?

Gears

• modified wheel-and-axle machines

• wheel with teeth along edge– larger gear=effort gear– smaller gear=resistance gear

Inclined Plane

• a sloping surface used to raise objects

• Work is same, but distance is increased, so force is less

• MA = length of slope (l)height of slope (h)

Screw

• An inclined plane that wraps in a spiral around a post

• Threads form a tiny ramp

Wedge

• An inclined plane with one or two sloping sides

• examples: chisels, knives, ax blades, etc.

• difference from ramp: the wedge is what moves through material

Identify as many simple machinesas possible in the following clip:

The End