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Pulleys Part 2: Complex Pulleys

Hey there!

Today we're going to be extending on the concept taught in the last experiment.


(If you've missed last week's experiment, I'd highly suggest starting there



Now, before we start, I'd like to inform you that this experiment is quite an elaborate one. It took me a while to make, hence the late upload.

But don't be disheartened, since you are completely free to take your time with this one.


Have fun along the way!


You will require


  • 1 Medium Sized Sheet Of Scrap Cardboard

  • 1 Bottle of Glue

  • 1 Compass

  • 1 Blue Ball Pen (Any pen is fine)

  • A String

  • 1 Ring Or Bangle


The Process



Step 1: Using a Compass, make 4 large circles of radius 3cm.





Step 2: Using the compass once more, draw 4 smaller circles of radius 2cm.



Step 3: Cut out these circles using a pair of scissors or a box cutter.



Step 4: Apply glue to all the smaller circles and stick them onto a bigger circle.




Step 5: Now apply glue to the other side of the smaller circles and stick the two halves of the pulley together



The final pulleys look like this.



Step 6: Using a pen or a nail, Make a large hole into the pulley. This is so that it can freely spin around.



Step 7: While the pulleys dry out. Use the remaining cardboard to make the supporting structure for the pulley system.


Cut out a piece that has a length of 26 cm and a width of 20 cm.



Now, to make things easier to follow, let's mark the edges of the board A, B ,C and D.


Mark A,B,C and D in a clockwise manner as shown above.


Step 8:

Now we need to mark the points of all our components.


Pulley 1- Mark a point that is 6cm away from side A and 6 cm away from side D.


This is the position of Pulley 1.


Mark this as Point P.


Singular Straw Support - Mark a point R that is 8 cm away from point P.


Also, mark another point Q that is 14.5cm away from point R.


Point Q will be required later.



Step 9: Take a straw and divide it into two segments of 4 cm each.



Step 10:


Ok so, First make two holes on the board at points P and R.


Second, mark a point S that is 2.5cm away from point Q.


Third, fix the straws in place at points P and R.


Phew, that was hard, but the good news we're close to being done!







Alright let's keep going.


Step 10: Affix one pulley at the straw in point P.



Step 11: Attach a weight to the second pulley using a string.


Here, ive used a small ring, you could also use something like a bangle.





Step 12: Place the second pulley at point S.


(Note: the image does not have the weight attached because It was inconvenient for the photos, but you will have to add the weighted pulley at the same position)



Step 13: Attach a string, that loops around the top of Pulley 1 goes below pulley 2 and is fixed upon the support straw.





Alright so we're finally done!


You will have to set this contraption up against a wall for it to work.


Pull on the string coming down from pulley 1 and watch as the the second pulley seamlessly moves up along the marked line.


Now, time for the actual science.


While this may look easy and straightforward, what we did today is very similar to real world pulley systems used in engineering.


Pulleys are really efficient at lifting heavy loads seamlessly.


In fact, Archimedes once pulled an entire ship using a complex pulley system like this.


So let's jump right into the scientific concepts surrounding this.


First of all what is a complex pulley system?


Last week, we learned about a simple pulley system. That consisted of only a single pulley.


A complex pulley system consists of 2 or more pulleys working in sync.


Now why is this useful?


Well, last week we learned about tension.


(If you missed last week's experiment, i highly suggest checking it out. Here's the link:- https://www.sciencerelyyours.com/post/pulley-mechanics-part-1 )


Tension is the governing force is pulley systems.


Now, complex pulley systems can be of many different shapes or forms. But all of them work towards one goal: redistributing the force of tension.


How do they do this? Let's employ a diagram to find out.





Now, here we build on last week's concept.


Clearly we can see that pulling on the rope produces tension in rope X which is colored blue.


But there's an additional layer here, the tension in rope X itself acts as a pulling force and generates additional tension in rope Y which is marked in Red.


Effectively the force of the pull creates a tension in rope X and the tension in rope X becomes a pulling force in and of itself and produces a tension in rope Y.


To visualise this effect let us imaginerooes X and Y as an individual pulley.





Here, the tension in rope X is similar to pulling on a simple pulley.


The end result is that the force of tension gets doubled in this setup.


At a small scale this is not that noticeable, but at larger scales this makes lifting heavier objects so much easier than before!


This has been great! See you all next week for the finale of the pulley saga!

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