SIMPLE MACHINES, FIXED AND MOVEABLE PULLEYS RST-LAB-013 REV B A) OBJECTIVE: To compare the mechanical advantage (MA) of fixed and moveable pulley systems. B) BACKGROUND Referring to the handout, a pulley is an example of a simple machine. A simple machine is a device that performs work by converting forces and distances. A simple machine has an attribute called a Mechanical Advantage (MA). The MA of a pulley system can be determined by the formula: C) PROCEDURE Step 1: Build the Fixed Pulley Assembly per instructions Step 2: Add 8 to 10 washers to the load and weigh the assembly per Figure 1. Record the weight in the Data Table under “Force Needed to Lift Load Without Pulley”. Step 3: Attach the load (weight) to the Fixed Pulley Assembly. Pull on the string to verify the load moves up and down smoothly. Figure 1 Step 4: Using the spring scale, pull down on the string and raise the load per Figure 2. Measure the force shown on the spring scale and record in the Data Table under “Force Needed to Lift Load With Pulley”. Step 5: Calculate the Mechanical Advantage of the pulley system using the formula above. Copyright © RST 2014. All Rights Reserved. SIMPLE MACHINES, FIXED AND MOVEABLE PULLEYS RST-LAB-013 REV B Step 6: Reconfigure to the Moveable Pulley Assembly as shown in the instructions. Repeat Steps 3, 4 and 5 as shown in Figure 3. Figure 2 Copyright © RST 2014. All Rights Reserved. Figure 3 Figure 4 SIMPLE MACHINES, FIXED AND MOVEABLE PULLEYS RST-LAB-013 REV B Note: We want to compare the amount of force required to lift the weight between the Fixed and Moveable Pulley systems. Use the same weight for both measurements- Do not change the amount of weight of the load. Enter the force required to lift the load with the pulley in the Data Table under “Force Needed to Lift Load With Pulley”. D) DATA TABLE Force Needed to Lift Load Without Pulleys Force Needed to Lift Load With Pulleys Mechanical Advantage Fixed Pulley Movable Pulley E) QUESTIONS 1) What is the Mechanical Advantage of the Fixed Pulley? What is the purpose of the Fixed Pulley? 2) What is the Mechanical Advantage of the Moveable Pulley? What is the purpose of the Moveable Pulley? 3) How could you increase the Mechanical Advantage of a pulley system? Copyright © RST 2014. All Rights Reserved. SIMPLE MACHINES, FIXED AND MOVEABLE PULLEYS RST-LAB-013 REV B PULLEYS: WHAT YOU NEED TO KNOW A pulley is a simple machine with a groove on its outside edge in which a cable (string) runs, At one end of the cable is the LOAD (also called the RESISTANCE or the weight you want to lift) At the other end of the cable is the EFFORT (the force you apply) There are two types of pulleys: FIXED PULLEYS and MOVEABLE PULLEYS FIXED PULLEYS change the direction of the EFFORT (Mechanical Advantage of 1) MOVEABLE PULLEYS decrease the EFFORT by converting force over a greater distance (ie trades force for distance) Mechanical Advantage = Force required WITHOUT pulleys / Force required WITH pulleys FORCE FORCE = LOAD 2•FORCE = LOAD FORCE = LOAD / 2 EFFORT = RESISTANCE MA = 1 Copyright © RST 2014. All Rights Reserved. EFFORT = RESISTANCE / 2 MA = 2 Rev B