What is Pulley: Definition and 1000 Discussions

A pulley is a wheel on an axle or shaft that is designed to support movement and change of direction of a taut cable or belt, or transfer of power between the shaft and cable or belt. In the case of a pulley supported by a frame or shell that does not transfer power to a shaft, but is used to guide the cable or exert a force, the supporting shell is called a block, and the pulley may be called a sheave.
A pulley may have a groove or grooves between flanges around its circumference to locate the cable or belt. The drive element of a pulley system can be a rope, cable, belt, or chain.
The earliest evidence of pulleys dates back to Ancient Egypt in the Twelfth Dynasty (1991-1802 BCE) and Mesopotamia in the early 2nd millennium BCE. In Roman Egypt, Hero of Alexandria (c. 10-70 CE) identified the pulley as one of six simple machines used to lift weights. Pulleys are assembled to form a block and tackle in order to provide mechanical advantage to apply large forces. Pulleys are also assembled as part of belt and chain drives in order to transmit power from one rotating shaft to another. Plutarch's Parallel Lives recounts a scene where Archimedes proved the effectiveness of compound pulleys and the block-and-tackle system by using one to pull a fully laden ship towards him as if it was gliding through water.

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  1. B

    Power transmitted to the second pulley

    A pulley 150 mm diameter is driven directly by an electric motor at 250 revs min–1. A V-belt is used to transmit power from this pulley to a second pulley 400 mm diameter against a load of 200 Nm. The distance between the centre of the pulleys is 600 mm, the included angle of the pulley groove =...
  2. H

    Rotational Dynamics: Pulley and mass system

    Homework Statement A 8.0-cm radius disk with a rotational inertia of 0.12 kg*m^2 is free to rotate on a horizontal axis. A string is fastened to the surface of the disk and a 10-kg mass hangs from the other end. The mass is raised by a using a crank to apply a 9.0-N*m torque to the disk. The...
  3. Ascendant78

    Work-Energy involving two forces on a pulley.

    Homework Statement Homework Equations The Attempt at a Solution Well, I tried working on this problems a few different ways and kept hitting a dead end. The work in "relevant equations" was my last attempt. I have spent well over an hour on this problem and I am ridiculously...
  4. J

    Can someone explain this please? Weird pulley with Tension

    Can someone explain this please?? Weird pulley with Tension Homework Statement See attached picture for problem Homework Equations n/a The Attempt at a Solution The answer is B. No idea why. Any help would be appreciated. Thanks!
  5. P

    Calculating Tension and Acceleration in a Pulley System with Applied Force

    Homework Statement A force of 25 N is applied on the pulley. M1 = 1.5 kg, M2 = 2.5 kg, light frictionless strings and pulley. a) What is the tension in the strings? b) What is the acceleration of the masses? c) What is the minimum Force to apply on the pulley so that M2 comes off the...
  6. J

    Consequences of an Oversized Pulley Bore Hole in Conveyor Systems

    What would happen if the bore hole of a pulley in a conveyor was significantly larger than the shaft like in the figure below: I would imagine if the RPM was high, the whole system would shake violently. However, what if the RPM was around 30 RPM. Would the conveyor still function properly...
  7. E

    Friction in a contact between a pulley and a string

    Homework Statement I need to find a formula for the friction in the system. I had a disk and a pulley connected to a rotation sensor on each side. I wrapped a pulley with a string and there was a small mass attached to the bottom. As I let that mass fall, it would fall and spin a pulley...
  8. A

    Tensions of cable over a pulley

    In the figure attached, we have one section which has three bars all pin-connected together and pin fixed on the ground. We have two pulleys connected with the section by string. And we have one string starting from the left fixed pin to the right fixed pin. I am thinking whether the tension...
  9. Avi Nandi

    How Do You Relate the Accelerations in a Disk and Pulley System?

    Homework Statement A disk of mass M and radius R unwinds from a tape wrapped around it. The tape passes over a frictionless pulley and mass m is suspended from the other end. Assume that the disk drops vertically. a. relate the accelerations of mass m and disk ,a and A, respectively to...
  10. T

    Angular Speed of Pulley (Spring, Pulley, Ramp)

    Homework Statement ---Find Angular Speed--- Homework Equations I = 1/2 mR^2 Ug = mgdsinθ Us = 1/2 kd^2 KE = 1/2 I w^2 The Attempt at a Solution Moment of inertia of reel = 1/2mR2 Kinetic energy of the reel = 1/2 mv2 = 1/2(1/2mR2) w2 KE = mgdsinθ (potential due to gravity) +...
  11. A

    Two masses on inclined plane with frictionless pulley

    Homework Statement A 1.00-kg aluminum block and a 4.00-kg copper block are connected by a light string over a frictionless pulley. The two blocks are allowed to move on a fixed steel block wedge (of angle 31.0°). The aluminum block is on the left side, on a flat plane. On the right is the...
  12. Saitama

    Simple problem involving pulley with mass

    Homework Statement The descending pulley (disc shaped) shown in the figure have a radius 20 cm and moment of inertia 0.20 kg-m2. The fixed pulley is light and the horizontal plane frictionless. Find the acceleration of the block if its mass is 1.0 kg.Homework Equations The Attempt at a Solution...
  13. C

    A unique rope and pulley problem

    A uniform heavy rope of length 2l goes over a small smooth pulley such that the right end has length (l+a) while the left end has length (l-a). The shorter portion is held and then released. Find the time taken for the rope to slip off the pulley.
  14. F

    Pulley Problem: Speed after falling a known distance

    A 1.2·kg block is tied to a string that is wrapped around the rim of a pulley of radius 7·cm. The block is released from rest. Assuming the pulley is a uniform disk with a mass of 0.37·kg, find the speed of the block after it has fallen through a height of 0.43·m. 2. F=mrω^2 and possibly F=mg...
  15. D

    How Do You Calculate Movement After Cutting a String in a Pulley System?

    Homework Statement Two masses 53gms and 45gms are connected by a light inextensible string passing over a smooth pulley and hung freely. Find a) the velocity after 3 seconds b) distance traversed in 3 seconds c) distance traversed in the third second d)if the string is cut after 3 seconds how...
  16. J

    How can I solve a dynamics problem involving a pulley, rod, and rotating masses?

    Homework Statement There is pulley which has a mass hanging from one side, and a rotating rod attached horizontally to the other (both by cables). The pulley has mass; Mp = 9.5kg and radius; Rp =0.2m. The block(A) has mass; Ma=10.9kg. The rod is L = 0.8m long and has mass=Ml7.9kg. The rod is...
  17. S

    Two blocks and a mass- and frictionless pulley

    The problem and solutions: http://i.imgur.com/hxlfbmZ.png I was able to solve the first two questions, but I guessed part C. For the first one, I thought of the two blocks as one unit (since there's no friction or air resistance). If they're both falling with the same acceleration, there...
  18. F

    Quick question on Pulley Force Problems

    Alright, so I'm doing this homework problem: "A 32·kg block is connected to an empty 1·kg bucket by a cord running over a frictionless pulley. The coefficient of static friction between the table and the block is 0.41 and the coefficient of kinetic friction between the table and the block is...
  19. P

    Figuring Out Forces in a Pulley System: What and Why?

    Homework Statement I don't really understand how to determine the forces in a pulley system. Like in this picture : http://postimg.org/image/4vxrf59ar/ How do you decide what forces are present for the pulley? Why isn't there a 375lb on the right side as well? What would be the pulley forces...
  20. M

    2 pulley system with three masses. Find the two outside masses.

    Okay, so I did a lab where we had a 2 pulley system that involved a string and three masses. The string is set up so it is in the shape of an m when put on the pulleys. The known mass is put on the middle string (m3) hanging down and the two outside masses (m1) and (m2) are unknown and are not...
  21. H

    Horizontal Pulley Question [Forces]

    Homework Statement An object is hanging by a [mass-less] string on a [mass-less] pulley from a cart on a desk with a mass of 1.8 kg. The cart has an acceleration of 2.5 m/s^2. Calculate the mass of the hanging object given that: a) There is no friction. b) There is a frictional force of...
  22. M

    Understanding Angular Acceleration and Velocity in Pulley Systems

    The question I am given is as follows: A string is wrapped around a pulley of radius 3.25cm, and a weight hangs from the other end. The weight falls with a constant acceleration 3.10m/s^2. 1. What's the angular acceleration of the pulley? 2. If the weight starts from rest 1.55m above the...
  23. P

    Can anybody check if I solved this correctly?(tension forces + pulley)

    Homework Statement The pulley can rotate and has no friction. Block m_2 is twice as big as m_1 Find the tensions, T_1, T_2, T_3 Homework Equations Newton's second lawThe Attempt at a Solution Tension 1: By creating a free body diagram only for the block, I got with Newton's second law...
  24. O

    How to Calculate the Mass of the Left Block in a Pulley System?

    Homework Statement The figure shows a 100 kg block being released from rest from a height of 1.0 m. It then takes 0.90 s to reach the floor. What is the mass of the block on the left? Illustration shows a pulley connected to the ceiling, with a block of 100 kg on the right, and a...
  25. P

    Finding the tension in a pulley that rotates

    Homework Statement m_2>m_1 The pulley rotates. Find the tensions, T_1, T_2, T_3 Homework Equations Newton's laws The Attempt at a Solution I know how to solve the problem if the pulley doesn't rotate because the systems would be in equilibrium (Newton's first law) and dividing...
  26. N

    Mass on Pulley problem need to find angular acceleration

    Homework Statement A string is wrapped around a pulley of radius 3.45cm , and a weight hangs from the other end. The weight falls with a constant acceleration 3.00m/s2 . What's the angular acceleration of the pulley? Homework Equations i'm writing out the equations i would think that...
  27. E

    Pulling mass with motor through pulley (with mass)

    Homework Statement http://puu.sh/4PDPV.png Homework Equations τ = I*α τ = r*F The Attempt at a Solution EDIT2: Nevermind, manipulated the torque equations wrong, got it now EDIT: Tried again and ended up with an actual answer, but still got it wrong :/ This is the FBD I used...
  28. A

    Spring - Pulley - Mass system. Proving omega is a certain value

    Homework Statement Hello, everyone. I am a starting physics student. I know a little bit of calculus and mechanics. I have been solving a lot of problems successfully, but I come back to being stuck on this one. I will show you what I have done and I hope you can be kind enough to give me a...
  29. C

    What is the correct acceleration for the inclined pulley problem?

    Homework Statement m1 has a mass of 47 kg and m2 has a mass of 35 kg. the coefficient of friction between m1 and the surface of the inclined plane are us=.42 and uk=.19 m1 is on an inclined plane angled 25 degrees A) if the masses are held in place and then released, will they start to move...
  30. C

    Pulley and Friction: Solving for Mass and Acceleration on an Inclined Plane

    Homework Statement m1 has a mass of 47 kg and m2 has a mass of 35 kg. the coefficient of friction between m1 and the surface of the inclined plane are us=.42 and uk=.19 m1 is on an inclined plane angled 25 degrees A) if the masses are held in place and then released, will they start to move...
  31. P

    Pulley and Circular Motion: Exploring the Mechanics of Rotation

    Delete this post
  32. karush

    MHB Calculating Angular and Linear Speeds of Pulley and Belt

    A pulley has a radius of $12.96\text { cm}$ it takes $18\text { s}$ for $56\text { cm}$ of belt to go around the pulley. (a) find the angular speed of the pulley in $\displaystyle\frac{\text {rad}}{\text{s}}$ well from $\displaystyle\frac{56\text { cm}}{18\text{ s}} \approx \frac{3.11\text {...
  33. A

    Blockk on a table with a pulley

    A 8.10-kg hanging object is connected by a light, inextensible cord over a light, frictionless pulley to a 5.00-kg block that is sliding on a flat table. Taking the coefficient of kinetic friction as 0.190, find the tension in the string. I don't know if my equations are right or where to go...
  34. Y

    How Does the Formula for Acceleration in a Pulley System Work?

    Homework Statement A 230-g air track glider is connected to a string hanging over a frictionless pulley. A 100-g mass hangs from the other end of the string. a) Draw force diagrams for the glider and the hanging mass. b) Find the acceleration of each. Homework Equations F=ma...
  35. C

    Solve Mobile Pulley System: Acceleration of 3 Masses

    Homework Statement A light smooth pulley is attached to a support a fixed height above the ground. An inextensible string passes over the pulley and carries a mass 4m on one side. The other end of the string supports a similar mobile pulley; over this passes a second string, carrying masses of...
  36. B

    Calculating Tension in Frictionless and Massless Pulley Systems

    Give the correct tension, T, in the marked rope for each situation. The rope is held so the system is stationary. All ropes and pulleys are massless and frictionless. Follow link for a picture of the pulley systems: http://i.imgur.com/2eBZpC3.jpg A) T = W B) T = W/2 C) T = W/3 D)...
  37. X

    Tension in pulley systems Concept help

    I need help understanding why in problems tension is modeled as T-mg = ma. I understand there are different variations, but the main concept is what I need help with. For example: If i have 2 masses hanging off a pulley (m1=5kg & m2=10kg) then m1 has a downward force of 49N down. The...
  38. E

    Acceleration of two blocks connected by a pulley

    http://puu.sh/4DtNc.png I solved this question, but I don't understand why this worked. I feel like for the final line in my solution it should just be divided by M1, not the combined mass of both blocks. Isn't this synonymous with just M1 being pulled up the ramp by a guy at the top...
  39. C

    Acceleration of 3 Blocks w/ Pulley

    Homework Statement There's a picture with the problem attached A block with mass m = 1.5 kg hangs to the right of two blocks with masses m2 = 2.2 kg and m1 = 1.2 kg which sit on a table. All three blocks are connected with a string and pulley. Neglecting the mass of the pulley, string and any...
  40. C

    Pulley system on an inclined plane with friction.

    Homework Statement Two blocks are connected by a thin inextensible string over a frictionless massless pulley as shown on the picture below The acceleration of gravity is 9.8 m/s2 Given that the two blocks move at 1.9 m/s under an acceleration of 4.1 m/s2, calculate the coefficient µk...
  41. mathmaniac1

    MHB Strings & Pulleys: Equilibrium, Find T1 & Explain

    The system is in equlibrium,find T1 and explain. Thanks.
  42. L

    Transfering power to a pulley attached to a rod

    A picture speaks a thousand words. In this video, at 41 seconds: [URL="http://www.youtube.com/watch?v=FBZWZfbxeJw"] Eugene R transfers power to a pulley attached to a rod but only the pulley spins. I am in the process of fabricating a pulley system like this. My question is: How is this done?
  43. T

    Pulley and cords tension physics

    The pulley in (Figure 1) is suspended by a cord C. Suppose that m1 = 1.0kg and m2 = 3.9kg . Determine the tension in the cord that supports the pulley C after the masses are released and before one hits the ground. Ignore the mass of the pulley and cords. I'm having trouble getting started...
  44. D

    Solve 2-Mass Pulley System Homework for Moving Blocks

    Homework Statement A massless string, passing over the frictionless pulley, connects the two masses as shown. Block m1 hangs vertically without touching the wall, but m2 slides along the wall with friction (μs = 0.61, and μk = 0.14). If θ = 53°, how many times heavier than block 1 must block...
  45. H

    Problem related to pulley system and velocity

    Homework Statement In the given figure if the masses A and B move down with a velocity 'v' at any moment then what will be the velocity with which mass W rises. A purely logical answer would be appreciated and please don't use calculus based approach, as I don't know calculus. Also...
  46. M

    Pulley Traction in Equilibrium

    Homework Statement Sum of downward forces exerted at A and B is 41lbs by the leg, what is the weight attached? Homework Equations None, really... The Attempt at a Solution Tension (T) throughout the system must be constant and equal to the weight (W). I first assumed that the leg...
  47. T

    Angular acceleration of a massless pulley

    Consider a massless string going over a massless frictionless pulley with masses M1 and M2 at the end of the string. The tension in the string would be same. The torque equation of the pulley says (T1-T2)=Iα .Now L.H.S is zero since T1=T2 and also I=0 . So,we have a condition 0=(0)(α)...
  48. P

    Tension and Force in pulley system

    Homework Statement Due to settlement of soil, a recently planted tree has started to lean. To straighten it, the cable system shown is used, where a turnbuckle on cable AB is periodically tightened to keep the cable taut as the tree gradually straightens. If the force in cable AB is 395 N...
  49. andyrk

    Friction on Pulleys: Axle or Surface?

    When we say of a pulley having friction, do we mean its axle about which it rotates has friction or the surface over which the string is wound has friction? Either way, if their is friction in a pulley, then when a string passes over the pulley, why does the string have different tension over...
  50. A

    Force on a massless inextensible string passing around a pulley

    I just can't get why for a massless inextensible string passing around a frictionless pulley we easily take T1=T2 (in fig.).My profs. never did explain this & jumped on further & when i ask them they won't answer saying it was very basic and other students say it's obvious. pls. help also pls...
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