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### Course: Physics library>Unit 18

Lesson 11: Simple machines explorations

# Pulleys

PLEASE NOTE: Some of the videos in this section are silent to allow the viewer to make their own observations about what is happening and respond to the questions posted below.
This video has no sound
1. Does this pulley arrangement give you a mechanical advantage?
2. If it does not give you a mechanical advantage why would you use it?
This video has no sound
1. Why were two fixed pulleys used at the top of the crane?
2. How far does the gondola on the right move compared to the one on the left?
3. Which gondola has the mechanical advantage?
This video has no sound
1. Why were two pulleys used on top of the gondola on the right?
2. How far does the gondola on the left move compared to the one on the right?
3. Which gondola has the mechanical advantage?
Simple machinesSee video transcript
Pulley Motorized 1See video transcript
1. How would you fix load tilt in the first part of the video?
2. What is your mechanical advantage in the pulley system shown at the end of the video?  (Hint: look at the movable pulley in the center of the load)

## Want to join the conversation?

• what's the point of a fixed pulley if there's no mechanical advantage?
• They can change the direction of a force not the actual speed.
• Whoo, first question ok! So looking at the figure in in the Simple Machines video specifically, I'm intuitively confused about how we "lost" 50N of force/ only have to exert 50N to pull a 100N block? What happened to the other 50N? Who's pulling that part? Also, if we assume that both pulleys are massless, what is the force on the "bar" holding the fixed pulley, and the force (tension) and direction of force on string 1 and 2?
• The 50N of force are not lost. When you pull with a 50N force to move a 100N block, it moves 1/2 the distance. The energy is conserved.
• This is really col but i don't know if I have all the stuff to make this,isn't there an easier way to make it.
• why not take a tube like object (a desk lamps adjustable neck) that is suspended in mid air. take a string and tie it round a eraser and then put the string over the top. that way when you pull the non eraser end the eraser will rise up. just like a pulley! YAY!
• Please review, and correct my thoughts:

Video 1:
Q2. Can use this, so that instead of lifting something above your head (against gravity), you can push something else down and work with gravity.

Video 2:
Q1. No idea, but I can see the effects i.e. A heavy gondola on the right can easily be raised. A force downward on the left, causes a much larger upward force on the right.
Q2. The right gondola moves approximately half the distance of the one on the left.
Q3. Since the right gondola moves half the distance, it implies that it also requires double the force. Therefore, a force on the left applies about double that force to the right, indicating a mechanical advantage to the right gondola.

Video 3:
Q1. So that the left can apply a large force over a small distance causing the right to travel a large distance with a minimal force applied.
Q2. The gondola on the left travels much less distance, approximately 1/4 the distance travelled by the right gondola.
Q3. The gondola on the left requires more force, therefore, it has the mechanical advantage.

Motorized Pulley Video:
Q1. Didn't quite understand what was done to even it out.. I had my own idea, but it wasn't the technique used. My idea: Add an identical second motor and wheels on the right side, which would cause the weight to tilt to the right. Thus, the same force is applied on either side.
Q2. I need to understand question 1 first! - But thoughts: The pulley wheel on the right requires the most amount of force, therefore, it has the mechanical advantage?
• Motorized Pulley Video:
The video's way was to connect the end of the string on the right side to the original motor so it reeled in the load from both ends, making it level.
The second question wasn't asking which pulley has mechanical advantage, but rather what the mechanical advantage was in terms of numbers. The "Simple Machines" video shows you how to calculate that.
• At , why does he bother to count the number of movable pulleys if all you need to know is the number of ropes? I know you need to know which are the movable pulleys, but why count them?
• why did you move the bateries when you fixed the floss
• what is better for lifting heavy objects a pulley or a lever
• Pulley pros:
1. Easy to transport (if you attatch a pulley system to a crane, for example)
2. Able to lift the object much higher

Cons:
2. Time-consuming to make

Lever pros:
1. Easy to make.
2. Object easily slides off the lever to destination

Cons:
1. It's almost impossible to push a lever and an object at the same time so it's not really great for transport.
2. Cannot lift objects straight (it will tilt to one side) so if you were carrying, say, a big basket of some sort with items inside, the items inside the basket could fall out due to the tilting.
3. Not great for lifting things off into the sky.

So to answer your question, it depends on what the situation is. Hope this helps!
(1 vote)
• How is the mechanical advantage equal to the number of strings?