1. Unit 6 – Lecture 1

2. Equations 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) (or… Force (resistance) / Force (effort)) 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 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 location of the Fulcrum, Resistance Force, and Effort Force (F) (R) (E)

10. 1 st Class Lever 1 st class lever: fulcrum in middle see-Saw (Teeter-Totter) pairs: scissors, pliers, hedgeclippers

11. 1 st Class Lever

12. Lever 2 nd class lever: load / resistance in middle door wheelbarrow arms pairs: shears, nutcracker

13. 2 nd Class Lever

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

15. 3 rd Class Lever

16. Review What was the equation relating FORCE to MA?

17. MA Lever The MA of a lever is calculated as: MA Lever = Effort Arm Length Resistance Arm Length (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

18. Practice What is the MA of a lever with an Effort Arm of 6 m and a Resistance Arm of.3 m? 20 Which type of lever does not increase the force output of the machine? third class If a lever has a MA of 9, and a force of 6 N is applied, how much force will the lever apply? MA = Force of Resistance / Force of Effort 9 = F R / 6 = 54 N

19. Practice What type of lever is each of the following?

20. Practice What type of lever is each of the following? claw hammer [prying a nail out] nut cracker human arm pliers tongs / tweezers wheel barrow

21. Answers

22. 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

23. MA Wheel&Axle MA = radius Wheel radius Axle Explains how to steer larger vehicles with less force

24. Practice What is the MA of a Wheel with a 50 cm radius connected to an Axle with a 2.5 cm radius? MA = radius(wheel) / radius(axle) = 50 / 2.5 = 20

25. 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 = 1MA = 2MA = 3MA = 4

26. 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

27. 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

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

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

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

31. Homework Complete Types of Levers w/s on page 4 If finishing early… 1) begin page 5 Simple Machines Matching 2) review vocabulary [due tomorrow – ch 5]