CONSTRUCTIVE THOUGHTS Simple Machines 7.2

Six Types of Simple Machines leverpulley wheel and axle inclined plane screwwedge

Lever A bar free to pivot about a fixed point fulcrum = fixed point effort arm = part of lever where F e is applied resistance arm = part of lever where F r is applied

The Mechanical Advantage of Levers MA lever = length of effort arm (L e ) length of resistance arm (L r ) 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 RE 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 –F e applied to larger wheel –smaller wheel (axle) exerts F r MA = radius of wheel (r w ) radius of axle (r a ) »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 machines as possible in the following clip:

The End