CONSTRUCTIVE THOUGHTS

1
CONSTRUCTIVETHOUGHTS

• Simple Machines
• 7.2

2
Six Types of Simple Machines

• lever
• pulley
• wheel and axle
• inclined plane
• screw
• wedge

3
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

4
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?

5
Three Types of Levers

• First class multiply force and/or direction
• Second class multiply force
• Third class cannot multiply force MA lt 1
  increases speed

6
Examples of Class Three Levers
7
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

8
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?

9
Gears

• modified wheel-and-axle machines
• wheel with teeth along edge
• larger geareffort gear
• smaller gearresistance gear

10
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)

11
Screw

• An inclined plane that wraps in a spiral around a
  post
• Threads form a tiny ramp

12
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

13
The End