1. Rube Goldberg Project Homework Project – you have to build it at home. Homework Project – you have to build it at home. Perform a task that is very simple in multiple steps using simple machines. Perform a task that is very simple in multiple steps using simple machines. 5 steps per person on the team 5 steps per person on the team Contraption must work from beginning to end without intervention, once started. Contraption must work from beginning to end without intervention, once started. Each step must be labeled Each step must be labeled Each step must include a simple machine Each step must include a simple machine Each step must have mechanical advantage calculated and labeled Each step must have mechanical advantage calculated and labeled Each step must have work calculated and labeled. Each step must have work calculated and labeled. Bonus Question: What is the efficiency of your machine (beginning to end) Bonus Question: What is the efficiency of your machine (beginning to end) Due Monday: 2/23 Due Monday: 2/23

2. Work, Power, Machines Chapter 9.1 & 9.2

3. What is Work? If I push on a lab table really hard for 20 minutes, is that work? If I push on a lab table really hard for 20 minutes, is that work? No No If I push on the wheeled cabinet lightly and it moves a little, is that work? If I push on the wheeled cabinet lightly and it moves a little, is that work? Yes Yes If I write on the white-board, is that work? If I write on the white-board, is that work? Yes Yes If I sit in my chair and do nothing, is that work? If I sit in my chair and do nothing, is that work? No No

4. What is Work? If I think really hard for 30 minutes, is that work? If I think really hard for 30 minutes, is that work? No No If I watch the TV for 2 hours, is that work? If I watch the TV for 2 hours, is that work? No No If I play Xbox for 10 minutes, am I doing work? If I play Xbox for 10 minutes, am I doing work? Yes Yes What is the common denominator between work and no work? What is the common denominator between work and no work?

5. What is Work? Work = Force x Distance Work = Force x Distance No force, no work No force, no work No movement, no work No movement, no work Work is measured in joules Work is measured in joules One joule is 1 Newton (force) x 1 meter (distance) One joule is 1 Newton (force) x 1 meter (distance) 1 N*m = 1J = 1 kg*m 2 /s 2 1 N*m = 1J = 1 kg*m 2 /s 2 1 N is 1 kg*m/s 2 1 N is 1 kg*m/s 2

6. What is Power? Which has more power? A semi truck or a fast sports car? Which has more power? A semi truck or a fast sports car? It depends It depends Which requires more power. Accelerating from 0 to 60 in 10 seconds or 6 seconds? Which requires more power. Accelerating from 0 to 60 in 10 seconds or 6 seconds? 6 seconds 6 seconds Why? Why?

7. What is Power? Power = Work/time Power = Work/time No work, no power No work, no power More time = less power More time = less power Less time = more power Less time = more power More power means doing the same work, faster More power means doing the same work, faster Power is measured in Watts Power is measured in Watts A Watt is 1 joule in 1 second A Watt is 1 joule in 1 second

8. Machines & Mechanical Advantage Which is easier: Which is easier: Lifting a car by your self to change a tire Lifting a car by your self to change a tire Using a car jack to lift the car Using a car jack to lift the car Obviously, using the car jack Obviously, using the car jack Why? Why? Because machines make it easier for us to do work! Because machines make it easier for us to do work!

9. Machines and Mechanical Advantage Machines don’t change the amount of work Machines don’t change the amount of work They might change the force They might change the force They might change the distance They might change the distance They might change the direction of the force They might change the direction of the force Usually, they change the amount of force by changing the distance Usually, they change the amount of force by changing the distance W = force x distance W = force x distance Change one up, the other goes down Change one up, the other goes down

10. Machines and Mechanical Advantage Both a car jack and a ramp reduce the amount of force required, by increasing the distance. Both a car jack and a ramp reduce the amount of force required, by increasing the distance. Mechanical advantage tell us how much the input force or distance is multiplied by the machine. Mechanical advantage tell us how much the input force or distance is multiplied by the machine.

11. Machines and Mechanical Advantage For any machine: For any machine: Input work = output work Input work = output work Forces may be different Forces may be different Distances may be different Distances may be different Work remains constant Work remains constant

12. Simple Machines Common Work Assistants

13. Six Simple Machines Inclined Plane Inclined Plane Wedge Wedge Screw Screw Lever Lever Wheel and Axle Wheel and Axle Pulley Pulley

14. Inclined Plane Inclined Plane: A Flat, Slanted Surface Inclined Plane: A Flat, Slanted Surface Purpose: Exert smaller force over larger distance Purpose: Exert smaller force over larger distance Ideal Mechanical Advantage: Ideal Mechanical Advantage: Length of incline / Height of incline Length of incline / Height of incline Example: Ramp Example: Ramp

15. Wedge Two Inclined Planes, Back to Back Two Inclined Planes, Back to Back Thick at one end, tapers to thin edge = strong output force Thick at one end, tapers to thin edge = strong output force Example: Axe, Knife, Splitting wedge, zipper Example: Axe, Knife, Splitting wedge, zipper

16. Screws Inclined Plane wrapped around a cylinder Inclined Plane wrapped around a cylinder Applies input force over a long distance Applies input force over a long distance Closer the threads, greater advantage Closer the threads, greater advantage Examples: Screws, jar lids, faucets Examples: Screws, jar lids, faucets

17. Levers Rigid Bar that pivots on a fixed object (the fulcrum) Rigid Bar that pivots on a fixed object (the fulcrum) Mechanical Advantage of lever: Mechanical Advantage of lever: Distance from fulcrum to input force / Distance from fulcrum to output force Distance from fulcrum to input force / Distance from fulcrum to output force Three classes of levers: Three classes of levers: First Class: fulcrum between input & output (pry bar) First Class: fulcrum between input & output (pry bar) 2 nd Class: Output between input and fulcrum (Wheelbarrow) 2 nd Class: Output between input and fulcrum (Wheelbarrow) 3 rd Class: Input between output and fulcrum (Rake) 3 rd Class: Input between output and fulcrum (Rake)

18. First Class Lever

19. Second Class Lever

20. Third Class Lever

21. Wheel and Axle Two cylindrical objects that rotate around a common axis Two cylindrical objects that rotate around a common axis Larger is wheel Larger is wheel Smaller is axle Smaller is axle Advantage: Multiplies force over longer distance Advantage: Multiplies force over longer distance Radius of Wheel / Radius of Axle Radius of Wheel / Radius of Axle

22. Pulley A grooved wheel with a rope A grooved wheel with a rope Pulley used to change directions Pulley used to change directions Fixed Pulley: pulley attached to a structure (advantage = 1) Fixed Pulley: pulley attached to a structure (advantage = 1) Movable Pulley: pulley attached to object you wish to pull (advantage = 2) Movable Pulley: pulley attached to object you wish to pull (advantage = 2) Pulley Systems: (block and tackle) combination of fixed and moveable pulleys Pulley Systems: (block and tackle) combination of fixed and moveable pulleys Advantage = number of sections of rope

23. Single Pulley Let’s Look at how to lift a large object: 100 lb block of something. We could lift it with a rope To lift it 10 meters in 1 second would take 454N of force To lift 10 meters would take 454J of work

24. Single Pulley If we add a single pulley to the system by running a rope over a wheel: We could lift it with a rope To lift it 10 meters in 1 second would take 454N of force To lift 10 meters would take 454J of work But now we are pulling DOWN or sideways instead of up – usually easier Gravity works with us instead of against us

25. 2 Pulleys – a Pulley System You can see that the weight is now suspended by two pulleys rather than one. That means the weight is split equally between the two pulleys, each one holds only half the weight, or 50 pounds (22.7 kilograms). you only have to apply 50 pounds of force (the ceiling exerts the other 50 pounds of force on the other end of the rope). Mechanical advantage is now 2 (2 output force for 1 input force)

26. Pulley Systems – Block and Tackle In this diagram, the pulley attached to the weight actually consists of two separate pulleys on the same shaft, as shown on the right. This arrangement cuts the force in half and doubles the distance again. To hold the weight in the air you must apply only 25 pounds of force, but to lift the weight 100 feet higher in the air you must now reel in 400 feet of rope. Mechanical Advantage depends on number of loops around the pulley 4 Loops = 4/1 advantage

27. Compound Machines Complex Machines Complex Machines Use two of more simple machines Use two of more simple machines Example: pencil sharpener uses wheel and axle to turn inside mechanism. Inside, axle turns gears, which turn two cutting screws (screw + wedge) cut wood. Example: pencil sharpener uses wheel and axle to turn inside mechanism. Inside, axle turns gears, which turn two cutting screws (screw + wedge) cut wood. GEARS: link one wheel & axle to another GEARS: link one wheel & axle to another