dynamics - the simple pulleys

8/12/2019 Dynamics - The Simple Pulleys

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Faculty of Manufacturing EngineeringUniversiti Malaysia Pahang

FKP-UMP 2012

BFF2821 Mechanics Laboratory

Title The simple pulleys Category Dynamics

Prepared by Matrix No.

Matrix No.

Date/Time

1. Introduction

A pulley is a wheel used to guide ropes or belts in selected direction, so that a force transmitted in one direction

can be changed to another direction. The pulleys spindle is small as compared to the diameter of the wheel, so

that it could be turned easily. Pulley can either be fixed (which have no relative movement) or movable.

Movable pulleys are supported by the rope passing under the pulley, thus forming a cradle. It is possible to liftthe heavy loads with reduced effort by combining fixed and movable pulleys.

The objective of this experiment is: 1.) to test the tension in a pulley cord as affected by the change in direction

of the cord, as it passes over a pulley and, 2.) to determine the mechanical advantage of a simple combination of

fixed and movable pulleys. Theoretically, the mechanical advantage of pulleys is given as

Mechanical Advantage (MA) = W/P

Where

W= the applied load, which is the weight of the weight hook plus the pulley block

P= the effort to just raise the weight, W.

2. Apparatus

Apparatus Quantity/Specification Figure

Knurled nuts 4

Adjustable hooks 2

Pulleys 2

Single pulley block 1


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Apparatus Quantity/Specification Figure

Weight hooks 2

Spring balance 10N

Weights 1 set NIL

Cord approximately 600mm length 1

3. Procedure

3.1 Preparation

1. Secure the mounting panel in the vertical position.2. Place the adjustable hooks and secure with nuts.3. Slide the hook up to give the shortest length.4. Place one pulley and secure with nuts.5. Hang the spring balance on the spring balance ring.

3.2 Test 1

1. Arrange the apparatus as shown in Figure 1. Add 1.9N to the weight hook to give a total weight of 2N(including the 0.1N of the weight hook) on the cord.

2. Record the weight shown on the spring balance.3. Add weights to give loads of 3N, 4N, and 5N and repeat step 1 and 2.

Figure 1: Experiment setup for Test 1


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3.3 Test 2

1. Arrange the apparatus as shown in Figure 2.2. This time, use a single cord and repeat as for Test 1 (due to the friction in the two pulleys the

apparatus will now be rather insensitive).

3. Record the weight shown in the spring balance.

Figure 2: Experimental setup for Test 2

3.4 Test 3

1. Weight the pulley block and record its weight.2. Arrange the apparatus as shown in Figure 3 with pulley block threaded on to the cord.3. Repeat the loads as in Test 1.4. Record the weight shown on the spring balance.


3.5 Test 4

1. Arrange the apparatus as shown in Figure 4.2. By applying loads as in Test 1, find the force, Pin each case to raise the load, W.3. Compare the reading of the spring balance with the force, P.


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4. Results

Tabulate your result on a piece of paper following the format as in Table 1.

Table 1:The weight, force and the mechanical advantage of simple pulleys

Weight, W(N) The effort to raise the weight, P (N) Mechanical Advantage

5. Discussions

Based on your results obtained, write your answers for the following questions:

1. What are the effects on the tension in a cord when they are used in pulleys?2. Part of the force (P) is used to lift the pulley block. The weight of the pulley block remains constant

although the weight used varies in size. Does this help to explain why the mechanical advantage

increased as the weight is increased?

3. A rather common way to mount a movable pulley is shown in Figure 5. Does this give the samemechanical advantage as the method used in Test 4? Explain.


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Figure 5:Another way to mount the movable pulley

6. Conclusions

Write your conclusions accordingly.

dynamics - the simple pulleys

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