Pulley Lab: Name:

Period:

Purpose: To determine the mechanical advantage and efficiency of a single-fixed pulley, a single-movable pulley and a block-and-tackle pulley system.

Hypothesis:

Pulleys are used to make work seem easier. There are two ways in which a pulley can make work easier.

1.   Pulleys can change the direction of the force

2.   Pulleys can multiply the force applied by spreading it over a longer distance.

There are three main types of pulleys:

1.   single - fixed pulley

2.   single moveable pulley

3.   Block and tackle - at least one fixed pulley and one moveable pulley in a system.

In this investigation you are going to determine the mechanical advantage and efficiency provided by each of the three types of pulleys. In order to do this you will have to calculate out the work input and work output of each pulley system and compare them to one another.

PROCEDURE: Single fixed pulley

1.   You will first need to set up a single fixed pulley system as directed by your teacher.

2.   Determine the weight of the object being lifted by attaching it to a Newton spring scale and recording this value in row B.

3.   Attach the weight to one end of a string and run it up and around a single fixed pulley attached to the top bar. Attach the short end of the string to spring scale.

4.   Using a meter stick, note the height at which the spring scale is attached to the string. Pull on the scale so that it moves at a constant speed and record the reading on the scale in row E.

5.   Move the weight being lifted up .1m (10 cm) from the tabletop to the bottom of the object. Record this in row C.

6.   Determine the distance that the scale was moved by subtracting the final reading from the initial reading on the meter stick. Record this value in row F.

7.   Calculate out the remaining rows using the formulas provided and your data.

Single moveable pulley

1.   Tie one end of a string to the top bar. Run the string through a pulley and attach the other end to a spring scale.

2.   Connect the pulley to the object being lifted and repeat steps 4-8 as you did for the single fixed pulley and record your data in the data table

Block and tackle pulley system: For this set up you will need 2 pulleys

1.   Tie a pulley to the top bar. Loop a string through this pulley. Tie one end of the string to the top of a second pulley and take the other end and loop it around the second pulley and then tie it to the spring scale. Connect the weight to the second pulley

2.   Repeat steps 4-8 as you did for the single fixed pulley and record your data in the data table

Complete the following data table:

A / Single fixed pulley / Single moveable pulley / Block and tackle
B / Resistance force-Weight of object being lifted(N)
C / Resistance distance -Height that the object is lifted(m) / .1 (10cm) / .1 (10cm) / .1 (10cm)
D / Work output (J) = force x distance(B x C)
E / Effort force (N) (Reading from spring scale as string is pulled)
F / Effort Distance how far scale is moved (m)
G / Work input (J) = force x distance (E x F)
H / Mechanical advantage (B/E)
I / Efficiency = work output/work input
(D/G) x 100

1.   Which pulley system required the greatest effort force? Explain why.

2.   Which type of pulley had the greatest mechanical advantage? Explain why this is.

(HINT: Think of which system you had to pull the most string through)

3.   What would be an easier way to determine the mechanical advantage of a pulley system?

(HINT: Think of how many strings are holding up the weight)

4.   Which pulley system was the most efficient? Is this what you expected?

5. Explain the best way that a mechanic could pull out a large truck engine by himself using the least possible amount of force