1. Simple Machines: Lever, Wheel & Axle, Pulley
Unit 6 – Lecture 1

2. Review Work = Force * distance measured in Joules [newton meters]
this remains true using effort force or resistance force
Power = Work / time
measured in Joules per second
Mechanical Advantage = Force(out) / Force(in)
Efficiency = Work(out) / Work(in) * 100

3. Machines A Simple Machine accomplishes the work in one motion.
A Compound Machine is made up of two or more simple machines. Most machines are compound machines.

4. Simple Machines There are six types of simple machines: Lever
Wheel-and-Axle
Pulley
Inclined Plane
Wedge
Screw

5. Helpful Note
ALL of the equations for the mechanical advantage of different types of machines will be given to you for the test [which will take place tentatively on Monday, 2/8].
Ideal vs. Actual Mechanical Efficiency
Ideal = according to the equation
Actual = taking into account the efficiency
ex: MA = 2 but machine only has a 94% efficiency
2 = the ideal MA
2* .94 = actual efficiency. MA = 1.88

6. Lever Bar Fulcrum A Lever is comprised of: a bar (straight or curved)
a fixed point called the fulcrum on which the bar pivots
Bar
Fulcrum

7. Lever
The distance from where the effort force is applied to the fulcrum is the Effort Arm of the lever.
this is where your effort is done
Effort Arm

8. Lever
The distance from the fulcrum to where the resistance force is applied is the Resistance Arm.
Resistance Arm

9. Lever There are three classes of levers:
class is determined by where the location of the effort force, resistance force (load), and the fulcrum

10. Lever 1st class lever: see-Saw (Teeter-Totter)
prying up a lid by pushing down on a bar
pairs: scissors, pliers, hedgeclippers

11. Lever
2nd class lever:
door
wheelbarrow arms
pairs: shears, nutcracker

12. Lever 3rd class lever: NOTE: MA = < 1
effort increases to increase distance of load
tweezers!
anything you swing
bat, sword, stick, golf club
brooms, rakes, mops

13. MALever The MA of a lever is calculated as:
MALever = Effort Arm Resistance Arm
(again, both in units of length, so there are no MA units)
The longer the effort arm, the more the MA [the better it is for you]
recall: increase distance, less force

14. Practice
What is the MA of a lever with an Effort Arm of 6 m and a Resistance Arm of .3 m?
Which type of lever does not increase the force output of the machine?
If a lever has a MA of 9, and a force of 6 N is applied, how much force will the lever apply?

15. Wheel-and-Axle
Wheel & Axle - a simple machine made of two circles of different diameters that rotate together.
The outer circle (wheel) is turned with less force over a larger distance so that the inner circle (axle) turns with more force over a shorter distance.
Ex. Steering wheels, door knobs, faucet handles

16. MAWheel&Axle MA = radiusWheel radiusAxle
Explains how to steer larger vehicles with less force

17. Practice
What is the MA of a Wheel with a 50 cm radius connected to an Axle with a 2.5 cm radius?

18. Pulley
Pulley - a simple machine comprised of a wheel with a rope or chain running around it.
The MA of a pulley system is equal to the number of ropes which support the object, because the weight is distributed.
MA = 1
no difference
MA = 2
no difference
MA = 3
no difference
MA = 4
no difference

19. Pulley There are two types of pulleys Fixed
do not move, merely redirect force
Moveable
attached to the object being pulled and multiply force
rises and falls with the object

20. Pulley
Block and Tackle System - a multiple-pulley system where large amounts of distance are converted into force.
composed of a fixed pulley & a moveable pulley
MA = number of supporting ropes

21. Practice 2 What is the effort force? [give in pounds of force] 35 lbs
What is the MA of this pulley system? 2
What is the effort force? [give in pounds of force]
35 lbs

22. Practice 3 What is the effort force? [give in pounds of force]
What is the MA of this pulley system? 3
What is the effort force? [give in pounds of force]
23.3 lbs

23. Practice
What is the Force Output of this pulley system?
50 N