1. What is a pulley?  A pulley is a wheel  A pulley uses rope that goes around the wheel (often, in a groove)  The rope attaches to objects  The other end of the rope has a force applied – Applied force is a push or a pull

2. Who has seen pulleys? …Pulleys are all around us… Flagpole   Elevator  Window shades and blinds

3. More examples  Sails and fishin g nets + rock climbing gear + clothes lines + gym training equipment  Cranes 

4. Why use pulleys?  Makes lifting things easier  Pulleys redirect force – Enables us to use gravity to help us (it is usually easier to pull down to lift something up)  Using several pulleys reduces the force required to lift an object – We have to use more rope and make the rope go further

5. Joe’s Problems

6. #1 Joe’s Got Problems …actually just one BIG problem. Hi again! His problem is his pooch, Rex. He’s one sick puppy. He’s also freakin’ HUGE!

7. #2 At the vet’s office… Joe has to get Rex up onto the examination table. Yike s!

8. #3 Joe’s been working out… …but not enough. Rex is just too heavy to lift.

9. #4 Joe learns his lessons well! Yo, uncle! WhaddooIdo? Use a PULLEY, Joe! I’m busy, so I gotta go!

10. #5 But Joe’s new at Pulleys …so he does what anybody should…a little research! Pulley – arrangement of wheel(s) and rope that reduce the amount of force needed to raise an object.

11. #6 He tries the first one Fixed pulley – uses one wheel to change only the direction of force. ceiling A “fixed” pulley wasn’t broken and is now repaired. “Fixed” in this sense refers to the fact that the wheel is attached to the ceiling and spins in place.

12. #7 Joe Pulls…

13. #8 And… …nearly breaks his back. Oh yeah! Joe remembers seeing that a fixed pulley just lets you pull down on rope instead of pulling up on the object. It doesn’t make Rex feel one ounce lighter! People do use fixed pulleys because pulling down on rope is easier on the body than bending over to pick the same weight up.

14. #9 Joe tries a different pulley A Running Pulley – uses a wheel hung on a rope to pull upwards, reducing the force by half.

15. #10 Joe Pulls… …and starts to lift Rex off the ground!

16. #11 But there’s one issue… …Joe can’t get Rex high enough to get on the table. On his tippy toes, Joe’s just not tall enough to keep pulling up and up and up on the rope. Rex only makes it halfway to the table top. 

17. #12 Joe hatches a plan… He realizes that both the fixed pulley and movable pulley have advantages and disadvantages… The fixed pulley doesn’t make Rex feel any lighter, but the Running pulley did allow Joe to lift his sick pooch off the ground. The problem with the running pulley was having to keep pulling up, up, up. However, the fixed pulley does allow you to pull down on rope.

18. #13 Hmmm…

19. #14 The Plan! Combine the ADVANTAGES of the fixed and running pulleys without suffering the DISADVANTAGES of either!

20. #15 Joe’s Research Joe uncovers a way to string this all together so that it helps him get the job done! Block and Tackle Pulley – a combination of fixed & movable Pulleys that reduces the force by half

21. #16 The Block and Tackle Pulley at Work

22. #17 Joe Pulls… …and starts to lift Rex off the ground! And the good news is that he is able to pull down on the rope so that he can just pull, pull, pull. Rex goes up, up, up.

23. #18 And Joe Has Just Accomplished… Reducing the amount of force it took to do work. Making sure he got to pull in a direction that’s easy for humans to do. Yes, he had to pull more rope, but that’s a trade-off worth making. But most importantly… This was possible due to mechanical advantage. The movable and double pulleys make work feel easier!

24. #19 ARF!

25. #20 One Final Point: As Joe was doing his research he realized … The more wheels & ropes, the better the pulley. You have to pull a ton of rope, but can easily lift heavy objects.

26. #21 And That’s…